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Vivid-Cruz
10-12-2003, 10:12 PM
So.. Does it.. I've decided that within the next few months .. i will be purchasing the 17" Tenzo-R AV-7's in GM... i believe they are 19lbs ea. Will I be able to notice a very large difference in overall power to the wheels?
K
p.s. here it is in the form of photochop..

02SilverSiHB
10-12-2003, 10:19 PM
yes wheel weight does matter. I wish I never got mine. I have 17's, they weigh 18.5lbs..may as well be 19lbs. They suck. My best 1/4 mile was 15.5 with i/h/e (intake is cai) when I had stock wheels/tires with sri and hp header I got a 15.5 at a higher mph than with the 17's.
Not only does weight matter, but size, more size, more rotational mass=slower acceleration.

Vivid-Cruz
10-12-2003, 10:32 PM
damn.. thats depressing.. i really dont want to sacrafice performance a great deal, yet i love the look of the 17" rims.. and is the difference only going to be a .5 sec at the track? if so im willing to sacrafice..i think

chubbychu
10-12-2003, 10:34 PM
Originally posted by 02SilverSiHB
yes wheel weight does matter. I wish I never got mine. I have 17's, they weigh 18.5lbs..may as well be 19lbs. They suck. My best 1/4 mile was 15.5 with i/h/e (intake is cai) when I had stock wheels/tires with sri and hp header I got a 15.5 at a higher mph than with the 17's.
Not only does weight matter, but size, more size, more rotational mass=slower acceleration.

if you keep the same diameter as stock will it be okay?

02SilverSiHB
10-12-2003, 10:39 PM
Originally posted by plainol2k2si
if you keep the same diameter as stock will it be okay?
no, the more rotational mass you get from the 17" rims will still slow you down compared to a stock size rim. as an example...a totally stock si with falken azenis was catching up with me at the end of the 1/4 mile just because the 17's I have. If the 1/4 mile had been longer he would have eventually caught up.

But if you don't care about .5 sec in the 1/4 mile go for it. It won't be that noticeable. people will argue that for autocrossing that a 17" doesn't hurt as long as it's light weight.
Overall, I stick with what I said before, I wish I had just stayed with 16's at the most.

glw
10-12-2003, 11:24 PM
Originally posted by 02SilverSiHB
no, the more rotational mass you get from the 17" rims will still slow you down compared to a stock size rim. as an example...a totally stock si with falken azenis was catching up with me at the end of the 1/4 mile just because the 17's I have. If the 1/4 mile had been longer he would have eventually caught up.

But if you don't care about .5 sec in the 1/4 mile go for it. It won't be that noticeable. people will argue that for autocrossing that a 17" doesn't hurt as long as it's light weight.
Overall, I stick with what I said before, I wish I had just stayed with 16's at the most. what about a 17" wheel and tire combo that weighs less than a stock 15" wheel and tire combo? :D who's mass is higher, then?

the problem then is finding inexpensive sticky tires at 17"...

BlasTech
10-13-2003, 07:20 AM
There's three factors to consider.

One, obviously is the wieght of the wheel/tire combo (regardless of size) does matter a bit. When I put my stock setup back on, I almost stall because I have to give it more gas to get going, compared to my aftermarket set. You will notice a difference if you drop say 5 or more lbs from the stock wheel/tire weight.

Two, is overall diameter. Anyone with 15" azenis is running almost 1" shorter overall diameter (hence they look somewhat winky) because thats the only 15" azenis offered. That shorter diameter will give a boost in accleration because it alters the gearing of the car, however it also sacrifices the tops speed by about 4%. With Azenis, when your speedo says 100mph, you're actually going 96mph. That same factor also means you shift at a 6% lower speed, too.

Finally, there's grip to consider. Though the Azenis are not drag tires, thier grip rating makes them a better-than-average tire for occasional 1320's, especially in launching.

My advise is to plan your wheel/tire combo around maintaining at the most the same of the stock setup.

Vivid-Cruz
10-13-2003, 10:10 AM
how much does the stock wheel/tire combo weigh?

bobdobbs
10-13-2003, 10:33 AM
About 40 pounds. The wheels are heavy (about 19.5 pounds), but the tires are relatively light, because of their size. Also, because the wheels are 15s, most of their rotating mass is closer to the center. A 19 pound 15 is not going to feel the same as a 19 pound 17.

My 15" Superleggeras are 10.5 pounds each, 32 pounds with tire. Plus, there's enough rubber that I'm not worried about denting a rim.

Burgh
10-13-2003, 11:44 AM
Just adding on... a lightweight 17" wheel may be better than a heavy-ass 15" wheel. But what if you got a similar lightweight 15" wheel? What if you got a 15" and a 17" that weighed exactly the same? Your rotational mass is farther out on a 17" wheel than a 15" wheel. I think that affects your performance as well.

Not too sure that the Azenis would make for a good drag tire. They have incredibly stiff sidewalls which may make traction at launch a bit trickier than a tire that flexes a little more to give you that contact patch you need. I don't drag race, but I think that this is why dragracers run really low pressures in the front. What the Azenis are good for is turn-in response and max lateral grip.

irrational
10-14-2003, 06:29 AM
Originally posted by bobdobbs
Also, because the wheels are 15s, most of their rotating mass is closer to the center. A 19 pound 15 is not going to feel the same as a 19 pound 17.
nicely put:)

Tenacious G
10-14-2003, 08:50 AM
Originally posted by 02SilverSiHB
no, the more rotational mass you get from the 17" rims will still slow you down compared to a stock size rim. as an example...a totally stock si with falken azenis was catching up with me at the end of the 1/4 mile just because the 17's I have. If the 1/4 mile had been longer he would have eventually caught up.

But if you don't care about .5 sec in the 1/4 mile go for it. It won't be that noticeable. people will argue that for autocrossing that a 17" doesn't hurt as long as it's light weight.
Overall, I stick with what I said before, I wish I had just stayed with 16's at the most.

wouldn't it be similar to inertia ... say like if you were spinning on a disc. you spin faster with your arms close to your body than you would if you spin with both arms extended. you weigh the same, but the more mass you put further away from the axis, the harder it is to get that mass spinning. or am I way off base here?

SiR Medic
10-14-2003, 09:16 AM
Originally posted by Tenacious G
wouldn't it be similar to inertia ... say like if you were spinning on a disc. you spin faster with your arms close to your body than you would if you spin with both arms extended. you weigh the same, but the more mass you put further away from the axis, the harder it is to get that mass spinning. or am I way off base here?


Definately... Spinning wheels also act as a sort of "gyroscope" on the car. The gyroscopic effect of big, heavy wheels would also offer a small amount of inertial resistance when the car wants to change direction.

Also the rotational inertia of larger, heavier wheels affects braking too. Big brakes are great, but the fact that you have to run 18's to fit them steals away some of the extra braking power.

One more thing. There is still some debate as to whether or not our 4-lugs can even handle wheels 17" and bigger.

My personal opinion on the whole matter: I'm going with a set of lightweight 16"s.

BlackNRedSi
10-14-2003, 09:22 AM
buy the 15inch spoon rims they are mad light, but mad expensive....

!@#$%
10-14-2003, 10:55 AM
i wouldn't dwell over wheel weight as much. After a week or less driving with the 17's you probably won't notice a difference. Even if it would make .1 or less in a 1/4 mile.

Vivid-Cruz
10-14-2003, 11:45 AM
thanks for all the very intuitive information .. It definetly gives me something to think about..I am going to definetly considering some 16's now.. i just like the look of a bigger tire.. and really wonder statistically.. how much of a difference it really makes..

bobdobbs
10-14-2003, 11:51 AM
Originally posted by Vivid-Cruz
I am going to definetly considering some 16's now.. i just like the look of a bigger tire.. and really wonder statistically.. how much of a difference it really makes..

Statistically, you are 93% more likely to prefer smaller wheels and bigger tires. The ratio of people who regret buying bigger wheels to people who regret buying smaller wheels is 27.3:1. The statistics are on your side. :D

Burgh
10-14-2003, 12:35 PM
If you plan on drag racing at a track, competitively, get the smaller wheels. If you're not going to race, just get whatever you like and don't sweat the details. :cool:

Gasp23
10-14-2003, 12:51 PM
Originally posted by Burgh
If you plan on drag racing at a track, competitively, get the smaller wheels. If you're not going to race, just get whatever you like and don't sweat the details. :cool:

I agree. If you are racing = smaller wheel. If you don't race and you just want your car to look sweet to your taste = do whatever you want.

bobdobbs
10-14-2003, 01:11 PM
You guys are implying you won't notice the difference from behind the wheel unless you're on a racetrack and that's just not true. Every time you accelerate or go over a bump, you feel big wheels with low-profile tires. And your chances of bending a rim go up the thinner your sidewalls are.

I'm not saying 17"+ wheels are always a bad decision, but saying racing is the only reason to go smaller is misleading. I never race, but chose 15" Superleggeras because of the benefits of ride comfort, acceleration, and the reduced load on the suspension in EVERY DAY DRIVING. Plus, they look far better than oversized tuner knockoff rims, IMHO.

Burgh
10-14-2003, 01:55 PM
Originally posted by bobdobbs
You guys are implying you won't notice the difference from behind the wheel unless you're on a racetrack and that's just not true.

Sorry if I came off sounding that way but that's not what I meant to convey. I was basically saying that if you're not a dragracer you don't care AS much about losing that 0.xx seconds in the 1/4. Sure, you'll feel your fatass 17"s in daily driving too, not just racing. But if you're not doing it for competition then the looks of a 17" may be worth taking that hit in performance. I'll never put 17s on my car cuz it'll make me slower and even less competitive than I already am. :D But if I wasn't in it for the competition, I probably wouldn't care.

bobdobbs
10-14-2003, 02:10 PM
Originally posted by Burgh
But if I wasn't in it for the competition, I probably wouldn't care.

I bet you would. :D

I put 17" ATS Planets on my old '00 Saab 9-3 and the performance difference from the stock 15s was annoyingly noticeable. Once I was going up a pretty steep hill and it felt like I was driving through molasses. You end up thinking, "Damn, I spent all this money on these wheels and tires and now my car is slower!" They looked better (than stock) but you can't see them while driving. :D

Burgh
10-14-2003, 03:05 PM
Originally posted by bobdobbs
I bet you would. :D


Ok, you got me, I would care. :D I don't put a dime into making my car look good but that's just me. I guess I should say that some other people wouldn't care about the slight loss in performance.

bobdobbs
10-14-2003, 03:12 PM
Maybe it's just me, but cosmetic mods that make your car look fast, but actually slow it down is at least partially the definition of "Rice". ;)

Tenacious G
10-14-2003, 03:46 PM
Originally posted by bobdobbs
Maybe it's just me, but cosmetic mods that make your car look fast, but actually slow it down is at least partially the definition of "Rice". ;)

i'll agree with that to a certain extent, but only if the cosmetic mod is way over the top. simply putting 17s on your car doesn't make you "rice," but 17" chromed-out spinning wheels is.

bobdobbs
10-14-2003, 03:52 PM
Originally posted by Tenacious G
i'll agree with that to a certain extent, but only if the cosmetic mod is way over the top. simply putting 17s on your car doesn't make you "rice," but 17" chromed-out spinning wheels is.

The other part of the definition is denial. I.e., it's always the OTHER guy who's a ricer. :D

DoMahMeGok
10-14-2003, 07:28 PM
Everyone here is talking about how the 17's would affect the accelleration and strip times, but won't 17's give the car better handling because of the stiffer sidewalls? I'm not too sure if its the sidewalls but I always heard handling would be increased with bigger tires, smack me right guys

chubbychu
10-14-2003, 09:26 PM
ehh...ill just stick with stock rims...and maybe powdercoat them white =o)...FOR NOW muahahah

glw
10-14-2003, 09:50 PM
ha, you guys are funny...

check out GRM's wheel test (autocross in a civic) at http://grassrootsmotorsports.com/plustest.html

17's turned faster lap times and were top choice by most drivers...

bobdobbs
10-14-2003, 09:59 PM
That test is seriously flawed since they didn't keep tire size constant as wheel size changed. The widest tires were on the largest wheels and they concluded the wheel size was the reason the lap times were the best. Not too convincing.

glw
10-14-2003, 10:07 PM
Originally posted by bobdobbs
That test is seriously flawed since they didn't keep tire size constant as wheel size changed. The widest tires were on the largest wheels and they concluded the wheel size was the reason the lap times were the best. Not too convincing. they used plus sizing... the same as we do to keep tire diameter same (or as close as possible) as stock... seriously flawed? i trust the GRM article more than this theorhetical conversation from a group of people that probably haven't tried all the various sizes. it seems "real world" enough to me...

bobdobbs
10-14-2003, 10:16 PM
No, read it again. They start out with 185-width tires (14"), then go to 195 (15"), 205 (16"), and 215 (17"). Plus-sizing varies the aspect ratio to keep the overall diameter the same, which is expected. By the time they got to the 17" they had almost an inch and a half more tread on the ground! Gee, I wonder why it performed better... :blushm:

glw
10-14-2003, 11:13 PM
Originally posted by bobdobbs
No, read it again. They start out with 185-width tires (14"), then go to 195 (15"), 205 (16"), and 215 (17"). Plus-sizing varies the aspect ratio to keep the overall diameter the same, which is expected. By the time they got to the 17" they had almost an inch and a half more tread on the ground! Gee, I wonder why it performed better... :blushm: bobdobbs, they did vary the aspect ratio and they used fairly proper plus sizing...

185/65-14 = 595.88mm diameter
195/55-15 = 595.37mm diameter (difference 0.09% smaller)
205/45-16 = 590.80mm diameter (difference 0.86% smaller)
215/40-17 = 603.75mm diameter (difference 1.31% larger)

if they used 205/40-17 (595.63mm diameter) they would actually produce a closer to stock diameter but my guess is that dunlop didn't make that size in the model they were using.

the 15" and 16" tires actually ended up with a smaller diameter while the 17" tire ended up with the largest diameter... this would actually give the 17" tire they used a disadvantage in the theorhetical argument presented here but it still outperformed the smaller tires.

choosing the 215/40-17 tire is exactly what many people that bought aftermarket wheels did. even though 205/45-17 is a better choice, it is a size that is just not as common.

so if your argument is that fatter tires rule, it makes the wheel size/weight issue moot, doesn't it? then just buy as wide a tire as you can fit under the car...

oh, and 30mm (215-185) is actually only about 1.18", a significant amount but not outside of what many tuners do today.

bobdobbs
10-14-2003, 11:33 PM
Originally posted by glw
so if your argument is that fatter tires rule, it makes the wheel size/weight issue moot, doesn't it? then just buy as wide a tire as you can fit under the car...

That's not my argument at all. Please, pay attention, because this will be the THIRD time I've said this: The GRM article does not keep the TIRE WIDTH (*NOT* DIAMETER) constant from smaller wheels to larger ones. They *have to* vary the aspect ratio to keep the diameter the same. That has nothing to do with what I'm saying.

Their argument is this: As wheel diameter increases, lap times go down. What they fail to mention is the amount of tread on the ground increases too because of the TIRES they chose, which probably has MORE to do with those lower lap times than wheel diameter. (duh?) That makes their comparison SERIOUSLY FLAWED. It's useless.

Finally, simply choosing as "wide a tire as you can fit under your car" regardless of wheel size, WILL NOT give you the best performance. By choosing a low-profile tire, you're substituting rubber and thin steel belts with a thick metal alloy, a heavier material. As you move the heavier material to the outside of your wheel/tire combination, the amount of torque required to get that mass moving increases, sapping performance. Hence, a 35 pound 15-inch 225-wide wheel/tire will perform better than a 35 pound 17-inch 225-wide wheel/tire because more of the mass in a 15-inch wheel is closer to the wheel center.

chunky
10-14-2003, 11:57 PM
Originally posted by glw
bobdobbs, they did vary the aspect ratio and they used fairly proper plus sizing...

185/65-14 = 595.88mm diameter
195/55-15 = 595.37mm diameter (difference 0.09% smaller)
205/45-16 = 590.80mm diameter (difference 0.86% smaller)
215/40-17 = 603.75mm diameter (difference 1.31% larger)

if they used 205/40-17 (595.63mm diameter) they would actually produce a closer to stock diameter but my guess is that dunlop didn't make that size in the model they were using.

the 15" and 16" tires actually ended up with a smaller diameter while the 17" tire ended up with the largest diameter... this would actually give the 17" tire they used a disadvantage in the theorhetical argument presented here but it still outperformed the smaller tires.

choosing the 215/40-17 tire is exactly what many people that bought aftermarket wheels did. even though 205/45-17 is a better choice, it is a size that is just not as common.

so if your argument is that fatter tires rule, it makes the wheel size/weight issue moot, doesn't it? then just buy as wide a tire as you can fit under the car...

oh, and 30mm (215-185) is actually only about 1.18", a significant amount but not outside of what many tuners do today.

so let me ask you this, if you had a 215mm wide 17" tire, and a 215mm wide 15" tire with identical overall diameters, which do you think would offer up better lap times?

the correct answer would be the 15" tires.

That whole GRM comparison is skewed b/c they did not isolate the variables properly. They varied WIDTH AND rim diameter. if they had just varied rim diameter, then it would be a valid comparison to cite in this sort of debate.

I personally am running 225/50/15 tires. Coincidentally, in that size you can buy several r compound tires from yokohama, toyo, michelin, kumho, hoosier, and pirelli. Try to find some r-compound in 215/40/17. . . . here's a hint - no one makes 'em.

Basically, if you're running a sport compact that came with 15" wheels stock, chances are, you're not going to be able to fit much wider than 225mm wide rubber into the stock fenderwell. So, that being the case, 225/50/15 is the ideal size for performance. Now if you have a bigger, heavier import that came with larger wheels stock, you can probably squeeze a 245mm wide tire into the fender well, in that case, you would go with a 16 or 17" wheel to ensure availiblity of competition tires.

In the end, you want the smallest rim that will fit over the brakes you require for your type of application, and the widest rubber your class allows.

glw
10-15-2003, 02:33 AM
Originally posted by bobdobbs
That's not my argument at all. Please, pay attention, because this will be the THIRD time I've said this: The GRM article does not keep the TIRE WIDTH (*NOT* DIAMETER) constant from smaller wheels to larger ones. They *have to* vary the aspect ratio to keep the diameter the same. That has nothing to do with what I'm saying.

Their argument is this: As wheel diameter increases, lap times go down. What they fail to mention is the amount of tread on the ground increases too because of the TIRES they chose, which probably has MORE to do with those lower lap times than wheel diameter. (duh?) That makes their comparison SERIOUSLY FLAWED. It's useless.

Finally, simply choosing as "wide a tire as you can fit under your car" regardless of wheel size, WILL NOT give you the best performance. By choosing a low-profile tire, you're substituting rubber and thin steel belts with a thick metal alloy, a heavier material. As you move the heavier material to the outside of your wheel/tire combination, the amount of torque required to get that mass moving increases, sapping performance. Hence, a 35 pound 15-inch 225-wide wheel/tire will perform better than a 35 pound 17-inch 225-wide wheel/tire because more of the mass in a 15-inch wheel is closer to the wheel center. bobdobbs and chunky,

i am paying attention and i completely understand your points about wheel size and keeping the weight closer to the hub, but i believe that the GRM article shows that to not be the case given their real life autocross lap times went down when the wheel size was increased while using plus sizing (as many people do today) to maintain tire diameter. i know this is counter to popular belief here on this board and what is passed around "word of mouth". i don't intend on hurting anyones feelings with this statement, but i value GRM's (and their experienced drivers) input over yours. here's why i think your arguments about increased weight on the perimeter don't jive.

bobdobbs:
your theory of
By choosing a low-profile tire, you're substituting rubber and thin steel belts with a thick metal alloy, a heavier material. As you move the heavier material to the outside of your wheel/tire combination, the amount of torque required to get that mass moving increases, sapping performance. Hence, a 35 pound 15-inch 225-wide wheel/tire will perform better than a 35 pound 17-inch 225-wide wheel/tire because more of the mass in a 15-inch wheel is closer to the wheel center.doesn't seem to match with what GRM found. they used larger wheels and wider tires and somehow got lower lap times. the weight shift you say is "sapping" performance must not have sapped enough to hurt lap times even with a wider tire. here's what i found - a plus size (http://www.toyo.com/tires/tire_basics/plus.html) wider lower profile tire weighs nearly the same as a narrower higer profile tire (ref: http://www.toyo.com/tires/tire_specsheet.cfm?id=1). in fact, tires weigh more (18-23lbs) than a decent wheel (13-15lbs) anyway which means that more weight is around the perimeter regardless of wheel size.

example-
average 15" wheel (15lbs) and 205/50/15 tire (20lbs) = 35lbs combo
average 17" wheel (17lbs) and 205/40/17 tire (19lbs) = 36lbs combo

it appears that the extra weight of the higher profile tire probably balances out the weight shift to the perimeter of the larger wheel...


chunky:

225/50/15 is the ideal size for performance.225/50-15 tires would appear to be significantly heavier than the 205/40-17 tires (>4lbs). this would probably offset any gains made by selecting a smaller wheel if weight was the issue.


glw comment:
although the GRM article increased tread width of the tire while increasing the wheel diameter size, this means that according to your theory they increased the wheel weight (including that at the perimeter) as well as increasing the weight of the tire - yet still achieved a faster lap time.

why? a wider tread? a lower profile tire? it was a fluke? it was the weather? it was tire pressures?

...take your pick, but it doesn't seem to be wheel weight/diameter reduction because the larger wheels and wider tires increased total weight (both wheel and tire) yet still outperformed the smaller ones.

02SilverSiHB
10-15-2003, 05:06 AM
Originally posted by chunky
so let me ask you this, if you had a 215mm wide 17" tire, and a 215mm wide 15" tire with identical overall diameters, which do you think would offer up better lap times?

the correct answer would be the 15" tires.

That whole GRM comparison is skewed b/c they did not isolate the variables properly. They varied WIDTH AND rim diameter. if they had just varied rim diameter, then it would be a valid comparison to cite in this sort of debate.

I personally am running 225/50/15 tires. Coincidentally, in that size you can buy several r compound tires from yokohama, toyo, michelin, kumho, hoosier, and pirelli. Try to find some r-compound in 215/40/17. . . . here's a hint - no one makes 'em.

Basically, if you're running a sport compact that came with 15" wheels stock, chances are, you're not going to be able to fit much wider than 225mm wide rubber into the stock fenderwell. So, that being the case, 225/50/15 is the ideal size for performance. Now if you have a bigger, heavier import that came with larger wheels stock, you can probably squeeze a 245mm wide tire into the fender well, in that case, you would go with a 16 or 17" wheel to ensure availiblity of competition tires.

In the end, you want the smallest rim that will fit over the brakes you require for your type of application, and the widest rubber your class allows.
I agree...also does GRM even say if they kept the same type of tire? and maybe their track times got better because they did it over and over again :)

chunky
10-15-2003, 05:12 AM
Originally posted by glw
bobdobbs and chunky,

i am paying attention and i completely understand your points about wheel size and keeping the weight closer to the hub, but i believe that the GRM article shows that to not be the case given their real life autocross lap times went down when the wheel size was increased while using plus sizing (as many people do today) to maintain tire diameter. i know this is counter to popular belief here on this board and what is passed around "word of mouth". i don't intend on hurting anyones feelings with this statement, but i value GRM's (and their experienced drivers) input over yours. here's why i think your arguments about increased weight on the perimeter don't jive.

bobdobbs:
your theory ofdoesn't seem to match with what GRM found. they used larger wheels and wider tires and somehow got lower lap times. the weight shift you say is "sapping" performance must not have sapped enough to hurt lap times even with a wider tire. here's what i found - a plus size (http://www.toyo.com/tires/tire_basics/plus.html) wider lower profile tire weighs nearly the same as a narrower higer profile tire (ref: http://www.toyo.com/tires/tire_specsheet.cfm?id=1). in fact, tires weigh more (18-23lbs) than a decent wheel (13-15lbs) anyway which means that more weight is around the perimeter regardless of wheel size.

example-
average 15" wheel (15lbs) and 205/50/15 tire (20lbs) = 35lbs combo
average 17" wheel (17lbs) and 205/40/17 tire (19lbs) = 36lbs combo

it appears that the extra weight of the higher profile tire probably balances out the weight shift to the perimeter of the larger wheel...


chunky:
225/50-15 tires would appear to be significantly heavier than the 205/40-17 tires (>4lbs). this would probably offset any gains made by selecting a smaller wheel if weight was the issue.


glw comment:
although the GRM article increased tread width of the tire while increasing the wheel diameter size, this means that according to your theory they increased the wheel weight (including that at the perimeter) as well as increasing the weight of the tire - yet still achieved a faster lap time.

why? a wider tread? a lower profile tire? it was a fluke? it was the weather? it was tire pressures?

...take your pick, but it doesn't seem to be wheel weight/diameter reduction because the larger wheels and wider tires increased total weight (both wheel and tire) yet still outperformed the smaller ones.

You're missing the point, The MAIN CONTRIBUTING FACTOR TO THE LOWER LAP TIMES OF THE 17" WHEEL IS DUE TO THE INCREASED WIDTH.

Now going from a 195mm wide tire to a 205mm wide tire might not seem like a big difference to you, but it makes a huge difference when you're driving at the limit.

And also, think about this, if a 15" tire weighs the same as a 17" tire, the 17" tire has MORE INERTIA. Why? b/c the mass is concentrated farther from the rotational center. Think lever arms here, the longer the lever arm, the greater the mechanical advantage. So same weight acting through a longer lever arm = more force applied to the fulcrum. So if you act on the end of the lever arm through the fulcrum, you INCREASE the effort required to move the mass.

There's no way around it, GRM knows this as well, what size tire did they run on their ep3 when they were autocrossing it? 225/50/15. Surprised? you shouldn't be, they went with the widest rubber they could fit in the fenderwells with the smallest wheels they could fit over the brakes.

And the average difference between 17" wheels and 15" wheels is more than 2lb. For instance, the oz superlegerra in 15x7 is 10.7lb, when you go to a 17x7, it ballons to 15.1lb, that's a difference of over 4lb.

Anyhow, the only useful notion from the GRM article is that tire width has a bigger impact than rim size. But if they isolated the variables, i think they would show clearly that smaller diameter wheels hold the edge in acceleration & do not give up any time on the track.

Burgh
10-15-2003, 08:47 AM
Yup, larger contact patch = better lap times. There's nothing surprising about the GRM results. The size of the contact patch dominated over the increased weight from the larger wheels. Obviously a 215-width tire is going to stick better than a 185-width tire. If they had figured out a way to keep the same tire, say 205s through the entire test (while adjusting the aspect ratio to make the overall diameter the same for all sizes of wheels) that would've been better.

glw
10-15-2003, 10:27 AM
if tire size matters so much more, why is everyone arguing that wheel weight REALLY matters (look at the thread title and everyones advice to buy a smaller wheel)?

you all just proved my point... other factors seem to matter more than wheel weight/diameter. tire tread pattern, tire contact patch, tire compound, and others are more important than the wheel weight/diameter...

and by the way, you can find 17" wheels that are 11lbs. my 17" volks are 13lbs. and the going rate for a decent wheel is 1lb per diameter inch.

Tenacious G
10-15-2003, 11:46 AM
Originally posted by glw
if tire size matters so much more, why is everyone arguing that wheel weight REALLY matters (look at the thread title and everyones advice to buy a smaller wheel)?

you all just proved my point... other factors seem to matter more than wheel weight/diameter. tire tread pattern, tire contact patch, tire compound, and others are more important than the wheel weight/diameter...

and by the way, you can find 17" wheels that are 11lbs. my 17" volks are 13lbs. and the going rate for a decent wheel is 1lb per diameter inch.

i don't think that was the original question. the original topic of the thread was should this guy get 17" wheels, not what width tire. and you're right, there are more factors to performance when it comes to wheels/tires than just weight and size.

however, the point the others are trying to make is that *all other things being equal*, a larger diameter wheel ultimately is detrimental to performace because you have more weight away from the axis on which the wheel spins. it will take more power to get a 13 lb. 17" wheel going than it will to get a 13 lb. 15" wheel going the same speed. and it's not theoretical, it's physics.

bobdobbs
10-15-2003, 11:56 AM
Originally posted by glw
if tire size matters so much more, why is everyone arguing that wheel weight REALLY matters (look at the thread title and everyones advice to buy a smaller wheel)?

you all just proved my point... other factors seem to matter more than wheel weight/diameter. tire tread pattern, tire contact patch, tire compound, and others are more important than the wheel weight/diameter...

and by the way, you can find 17" wheels that are 11lbs. my 17" volks are 13lbs. and the going rate for a decent wheel is 1lb per diameter inch.

Wrong. Wheel weight/diameter WITH COMPARABLE TIRES is the single most important factor in wheel/tire performance. The GRM article's conclusion is wrong, regardless of how highly you think of them, because it ignores the difference in tires. With similar tires, the best 15" wheel will outperform the best 17" wheel on our cars. And 17s have no advantage in tire selection in 225-width. 15s do.

Your 13-pound 17" Volks with 225-width tires will not be able to keep up with a 10.5-pound 15" Superleggera, let alone a 9-pound 15" Enkei RPF1 for two reasons: 1) Your 17s have more mass toward their outer diameter and 2) they're overall heavier. I'm sorry, that's physics.

BlasTech
10-15-2003, 12:13 PM
I think as long as the weight and width is the same, the performance differences between 15,16, and 17 would be close to negligable for most people.

Where one is better in one way (less gyroscopic force), the other is better in the other way (less sidewall flex).

I usually advise people who are concerned with performance to go with 15's for two reasons.

1. Its easier and cheaper to find lightweight 15" wheels.

2. Its cheaper to go through performance tires more often with 15" wheels.

rs_1101
10-15-2003, 01:36 PM
no dobbs is right. its a simple question of torque. in a 17 inch rim, more of the mass is centered on the outside, which means that the car has to push harder to move that wheel in a rotational distance.
here:\
lets say you have like.. idk 5 oz weights that rotate from an imaginary point.
if one weight is 10" from the center
and one is ohh.. idk 17" from the center.. it takes more force to move the 17" one b/c you have to move the 17" weight in a larger circle, which means your actually moving it a larger distance. if you rotate both weights 180`, then the one thats 10" has traveled a shorter distance and therefore requires less force to move it.

but it does matter how the weight is distributed and i dont think too many wheel companies disclose weight distribution in their cars

ahhhonda
10-15-2003, 01:42 PM
I think most people are understanding the concepts involved so far, but this might help some of those who are not understanding it yet..

Do you remember the merry-go-round on the playground? Were you ever the unlucky one who was required to push it because you were the strongest or fastest? Let's use that as an example. Let's say you have 4 friends riding on the merry-go-round and you are pushing it but not riding it. Your four friends are on the outside edge of the merry-go-round when you start to push it...it's very hard to get it going and harder to get going fast.. If your four friends sit towards the center of the merry-go-round it's much easier to get going, and going fast. Now after you have it going fast lets say your friends move.. If they are inside and move outside, the merry-go-round will slow down. If they are outside and move inside the merry-go-round will speed up. This shows how much the placement of the wieght affects rotating devices. These same principles are the same ones that let an ice skater speed up and slow down while they are doing a piroette(sp?). So even when wieght is a constant, Where that weight is distributed makes a difference.
The answer to the posted question about weight is that yes, it does really matter.
Now as far as tires and wheels are concerned, there are many other factors in the equation: the contact patch(width of the tire mostly affecting this, but also tire pressure); sidewall flex(manufacture of the tire mostly affecting this, but also tire pressure again); tread pattern; and tread compound. All of these factors affect the grip of the tire and affect how much of the tire effectively stays on the ground. If someone could do a test where the weight distribution, tire width, sidewall strength, tread pattern and tread compound were all the same, but on a 15" 16" and 17" platforms, I believe they would have almost identical results. But things just don't work out that way. In order to keep the same overall diameter, the sidewall height must change, therefore sidewall strength varies. Weight distribution also changes as the tire and wheel are different. If you think of where the most of the metal is in a wheel, it's in the center hub area and the outer edge where it meets the tire. That means that more weight is farther outside on a bigger wheel. Also on the tires, if you have a 205/60 series 15" tire that weighs 23-lbs, and a 205/40 series 17" tire that weighs 23-lbs, the 23-lbs on the 15" tire is distributed along 123MM of the outer diameter of the wheel/tire combo and the 23-lbs on the 17" wheel/tire combos is distributed on the outer 82MM. That's more weight on the very outer diameter of the tire, which gives it more rotational inertia, which means it takes more work to accelerate and or decelerate that tire/wheel combo. Honestly, I'm not trying to confuse anyone..I hope this helps some of you. :)

chunky
10-15-2003, 07:48 PM
Originally posted by glw
if tire size matters so much more, why is everyone arguing that wheel weight REALLY matters (look at the thread title and everyones advice to buy a smaller wheel)?

you all just proved my point... other factors seem to matter more than wheel weight/diameter. tire tread pattern, tire contact patch, tire compound, and others are more important than the wheel weight/diameter...

and by the way, you can find 17" wheels that are 11lbs. my 17" volks are 13lbs. and the going rate for a decent wheel is 1lb per diameter inch.

In that particular comparison, tire width determined the winner, and they claimed to some degree that the rim size was responsible for the advantage as well. That is an incorrect assessment.

As far as advantages of 17" over 15", there are none. Some people will say that the shorter sidewall creates more favorable slip angles, but on a car as light as ours, the effect is negligible, especially with the stiffer sidewalls that are availible today. The only time you'd want to run a 17" wheel is when your racing class mandates the wheel/tire size - like speed world challenge - all the cars run on the same size wheel with the same size tire. They're currently set at 17", but are going to increase the requirement to 18" next year. The reasoning is not b/c 18" perform better, but b/c they are trying to reflect what is "cool" on the scene. I'll put it this way, the ultimate 4 wheel vehicles use 15" wheels with 300+mm wide rubber and sidewalls that are taller than what come stock on the ep3 - F1 cars are governed for overall tire diameter, but it doesn't seem to stop them from being the fastest track cars on the plannet.

bobdobbs
10-15-2003, 08:13 PM
Originally posted by chunky
I'll put it this way, the ultimate 4 wheel vehicles use 15" wheels with 300+mm wide rubber and sidewalls that are taller than what come stock on the ep3 - F1 cars are governed for overall tire diameter, but it doesn't seem to stop them from being the fastest track cars on the plannet.
Actually, FIA regs specify 13" wheels but that just proves your point further: the fastest track cars on the planet use small wheels.

MrCivic03
10-15-2003, 08:19 PM
i am just chimming in i think what u want it for is what u should get. if he likes the looks he doesnt really care if they weigh more... plus i raced my mom the other day(drives a g35) i can take her off the line, because it is harder to get her tourque to the ground on stock heavy 17" but when she does she is gone so does that go here?**yes i kno the difference in HP and TQ btwn the two cars also**

Vivid-Cruz
10-15-2003, 09:02 PM
Originally posted by bobdobbs
Statistically, you are 93% more likely to prefer smaller wheels and bigger tires. The ratio of people who regret buying bigger wheels to people who regret buying smaller wheels is 27.3:1. The statistics are on your side. :D

haha.. fkn bobdobb.... always count on your for infomaritve and usually, facetious advice = )...

Rey
10-15-2003, 10:01 PM
This thread can easily be made into a book. Or at least into a informative debat on TV.

BSEVEER
10-15-2003, 11:15 PM
Doesn't it ultimately come down to comparing a specific 15" wheel/tire combo to a specific 17" wheel/tire combo? I think it would be possible to get better performance from a lightweight 17" set up than you would get from a heavier 15" set up.

chubbychu
10-15-2003, 11:19 PM
bobbdobbs sure does waste a lot of time on this forum typing out all his little facets of information. lol

so summarzing

smaller rims-better accel, look small
Bigger rims- takes longer to accel, looks goooooooood!

cinprogrunt
10-16-2003, 12:02 AM
I know I am new to this forum, but would like to intervene without burning any bridges. . On my EP3 I have 17" SSR Comp Wheels and cheap Kumho tires. When I made the change I notice a HUGE difference for the better. The car accelerated faster, handled better and stopped more easily. Given, the wheels only weigh 12.5 lbs compared to the 19.5 lb stock wheels, if done correctly benefits can come from plus sizing.

I would have to agree that Grassroots did do a poor job in their wheel and tire comparison as it was advertised. Overall wheel width, diameter and tire sizes were not chosen wisely for a true comparison.

On the other hand, in defense to Grassroots' article, the amount of time and money to truly compare different wheel widths, diameters, and tire sizes would be a massive endeavor, on top of it all keeping in mind all the different wheel and tire weights would be mind boggling. To then come up with an organized and logical way of putting it on paper in a way that anyone could understand would almost not be worth the effort.

As for which tire/wheel size, weight combination is the best, I think there is no answer for every situation. Personally, I feel I have hit it on the nose from performance and style perspective. I have kept my wheel/tire weight down buy using light wheels(Performance), and have kept in consideration I wanted the car to look good too(Style). At least I think that it looks good. To each his/her own.

Thanks

bobdobbs
10-16-2003, 12:08 AM
Originally posted by plainol2k2si
bobbdobbs sure does waste a lot of time on this forum typing out all his little facets of information. lol

Hey, did you ever stop to think about what we consider solid material in an atom -- the nucleus -- is really very, very small compared to the size of the electron cloud, which is just a bunch of little electrical junk flying around? And it's collections of atoms that form molecules that make up materials that we touch and use in our every day lives? And when you start putting all these atoms together, their electron clouds interact, but their nuclei stay far apart. So, really, the stuff that we consider solid is really made up of some very small nuclear material (the nuclei) and a bunch of electrons flying around in much larger "clouds". And the fact that you can't, say, put your hand through a tree is because the electrical forces in the atoms in your hand being opposed by the atoms that make up the tree. So, really, matter -- the stuff around us -- is made up of mostly empty space. Weird, huh?

What were you saying, plainol? :D

glw
10-16-2003, 04:46 AM
in general it appears that for the same model of tire a XXX/60-15 tire weighs more than a XXX/40-17 tire by two or more pounds. this seems reasonable considering the extra belts and rubber needed.

explain to me how this extra tire weight effects the weight of the wheel/tire combo? does it add weight near the hub or out past the wheel on the perimeter?


NOTE: a 235/60-15 tire and a 235/40-17 tire will have a very different number of revolutions per mile and doesn't follow the popular "plus sizing" concept. it is not necessarily being recommended and used here for arguments sake.

chunky
10-16-2003, 10:23 AM
Originally posted by glw
in general it appears that for the same model of tire a XXX/60-15 tire weighs more than a XXX/40-17 tire by two or more pounds. this seems reasonable considering the extra belts and rubber needed.

explain to me how this extra tire weight effects the weight of the wheel/tire combo? does it add weight near the hub or out past the wheel on the perimeter?


NOTE: a 235/60-15 tire and a 235/40-17 tire will have a very different number of revolutions per mile and doesn't follow the popular "plus sizing" concept. it is not necessarily being recommended and used here for arguments sake.

well, first off, i'll point out that if the overall outside diameter is different, it's difficult to accurately compare tire weights. If you compare the 205/60/17 tire size to a 205/40/17 tire size, the overall difference in diameter is 31.1mm or about 1.2" GREATER for the 15". That 1.2" of greater diameter is what makes the tire heavier.

Typically, the 15" & 17" tires of the same width & outer diameter are very very similar in weight as most of the weight of the tire is on the tread. The Difference in sidewall hieght would save some weight except that the shorter sidewall requires different construction which means added weight.

glw
10-16-2003, 02:08 PM
Originally posted by chunky
well, first off, i'll point out that if the overall outside diameter is different, it's difficult to accurately compare tire weights. If you compare the 205/60/17 tire size to a 205/40/17 tire size, the overall difference in diameter is 31.1mm or about 1.2" GREATER for the 15". That 1.2" of greater diameter is what makes the tire heavier.

Typically, the 15" & 17" tires of the same width & outer diameter are very very similar in weight as most of the weight of the tire is on the tread. The Difference in sidewall hieght would save some weight except that the shorter sidewall requires different construction which means added weight. understood. earlier in this discussion it was mentioned that a smaller wheel with the same width tire should be used in the GRM test. maybe i can get my answer this way... what size 15" and 16" tire should have been used on the GRM test (considering 215/40-17 as the target) for it to be acceptable for you guys?

another question... which is heavier part; the wheel or the tire?

15" performance wheel = ?lbs
15" performance tire = ?lbs
17" performance wheel = ?lbs
17" performance tire = ?lbs

Vivid-Cruz
10-16-2003, 02:37 PM
I have a physics midterm tomorrow and i am considering the hour I spent reading this thread, 'Study Time', but you have all confused the phuck out of me.. not in a conceptual sense but more in a "what the fuck do i want to get out of my car?" way. I'm thinking if i compromise and get some 16" performance wheels, appearance may not differ much from the 15" and then ill wonder why i just didnt buy better tires..who knows..Im going to have to give this one some thought.. maybe get some coilovers while i contemplate..AHH!!


screw it.. im going to powder coat stockies white and call it a day..lol

chunky
10-16-2003, 09:53 PM
Originally posted by glw
understood. earlier in this discussion it was mentioned that a smaller wheel with the same width tire should be used in the GRM test. maybe i can get my answer this way... what size 15" and 16" tire should have been used on the GRM test (considering 215/40-17 as the target) for it to be acceptable for you guys?

another question... which is heavier part; the wheel or the tire?

15" performance wheel = ?lbs
15" performance tire = ?lbs
17" performance wheel = ?lbs
17" performance tire = ?lbs

first, the tire size question. assuming the 215/40/17 is the target overall diameter size (603.8mm):

215/50/15 = 596mm
215/45/16 = 599.9mm

All of those are within +/- 2% of one another, so gearing advantage should be negligible. If GRM had used those tire sizes, it would have been a fair comparison - but that 15" size is very very rare if it can be found at all. A better size would have been just to use a 205/xx/xx assortment of tire sizes. 205 is common for 15, 16, and 17 inch sizes. I would sugges the following sizes if one were to conduct a comparison with an ep3:

205/45/17
205/50/16
205/55/15

The yokohama AVS es100 is made in all of those sizes. THAT would make for a fair comparison - just get 3 sets of wheels made by the same company, a set of 15x7, 16x7 and 17x7, 3 sets of tires, and have at it. I think you'd be very surprised at how small the final difference in times would be - but on an auto-x type course, i'd expect the 15" to command a significant margin over the 17", and i'd expect that margin to slim a bit on a road race type course.

And the 2nd question:

The tire is almost always the heavier part by far. a 225/50/15 tire weighs about 20lb. A 15" performance wheel would be no more than 12 or 13lb with significantly lighter (as low as 8lb) availible.

With 17" wheels, the tire weight is about the same, a 225/40/17 tire would weigh about 20lb as well, with the wheel coming in at an average of 15-17lb with much lighter (as light as 11-12lb) availible.

So the difference in actual tire weight would be negligible, but the location of the mass is what's important. With the 20lb 17" tire, the mass is centered farther out from the hub than the 15"

eurosteez
10-16-2003, 10:23 PM
Originally posted by cinprogrunt
I know I am new to this forum, but would like to intervene without burning any bridges. . On my EP3 I have 17" SSR Comp Wheels and cheap Kumho tires. When I made the change I notice a HUGE difference for the better. The car accelerated faster, handled better and stopped more easily. Given, the wheels only weigh 12.5 lbs compared to the 19.5 lb stock wheels, if done correctly benefits can come from plus sizing.

;)

Ok some more fuel to the fire. If you have a 15" tire that weighs 12lbs compared to a 17" that weighs 12 lbs which would perform better? Another way to phrase the question, Does wheel diameter effect wheel to ground area ratio? It should help a little right? Of course centrifugal force is benefiting the 15" tire but I'm talkin about grip.

chubbychu
10-16-2003, 10:37 PM
Originally posted by bobdobbs
Hey, did you ever stop to think about what we consider solid material in an atom -- the nucleus -- is really very, very small compared to the size of the electron cloud, which is just a bunch of little electrical junk flying around? And it's collections of atoms that form molecules that make up materials that we touch and use in our every day lives? And when you start putting all these atoms together, their electron clouds interact, but their nuclei stay far apart. So, really, the stuff that we consider solid is really made up of some very small nuclear material (the nuclei) and a bunch of electrons flying around in much larger "clouds". And the fact that you can't, say, put your hand through a tree is because the electrical forces in the atoms in your hand being opposed by the atoms that make up the tree. So, really, matter -- the stuff around us -- is made up of mostly empty space. Weird, huh?

What were you saying, plainol? :D

showoff

glw
10-16-2003, 11:34 PM
thought it was confusing before? try this on...

[quote]A 10 lb reduction of wheel/tire weight will result in a total overall apparent effect of reducing vehicle weight by about 65 lbs and at absolute maximum, 80 lbs.

The analysis follows:


Question: What is the effective additional mass of wheels/tires due to their rotation?

For the vehicle in motion, the kinetic energy is given by:

Ekinetic =

bobdobbs
10-17-2003, 12:41 AM
That's excellent. He's shown how weight distribution affects the effective mass. If a 15" wheel has, say, an Reffective/Rtread of 80%, a larger wheel will have an Reffective/Rtread of maybe 90%. So, instead of Mwheel,effective being Mwheel*1.64, Mwheel,effective is Mwheel*1.81. Ouch.

eurosteez
10-17-2003, 07:15 PM
Originally posted by bobdobbs
Hey, did you ever stop to think about what we consider solid material in an atom -- the nucleus -- is really very, very small compared to the size of the electron cloud, which is just a bunch of little electrical junk flying around? And it's collections of atoms that form molecules that make up materials that we touch and use in our every day lives? And when you start putting all these atoms together, their electron clouds interact, but their nuclei stay far apart. So, really, the stuff that we consider solid is really made up of some very small nuclear material (the nuclei) and a bunch of electrons flying around in much larger "clouds". And the fact that you can't, say, put your hand through a tree is because the electrical forces in the atoms in your hand being opposed by the atoms that make up the tree. So, really, matter -- the stuff around us -- is made up of mostly empty space. Weird, huh?

What were you saying, plainol? :D

So theroretically bodbo, we could condense this planet into oh...say a square inch? or even smaller? it could be condensed so much it went negative(blackhole)?
But what does this have to do with you posting alot?

DownTheHatch
10-17-2003, 10:05 PM
There's a simple experiment you can do that will prove to all of you the difference of weight vs. diameter.

If you have an office chair that rotates, give yourself a good push with your legs all the way out. Now gradually bring them closer to your body (the center of the rotating axis) as you spin. The speed at which you are spinning will increase as you pull your legs in, there is less rotational mass.

Now, take something that weighs about 10 pounds and place it on your lap, infact, add as much weight as you want, getting yourself started will be increasingly tougher but once you're going, your legs will be determine how much freer you will spin.

Weight = Intertia (force holding an non-moving object in its place) You will notice this when you try to launch the car, say at the drag strip, with heavy wheels you will have a really hard time getting that car to go anywhere quickly, the same thing applies at highway speeds, when you goose the pedal you will not get as quick of a response if the wheels were lightweight. Kind of like the difference between throwing a bowling ball or throwing a basketball.

Diameter = Acceleration (rate at which an object gains speed)
If you've ever worked with gearing, the sizes always determine the speed at which the gear rotates, a smaller sprocket spins 2x or 3x quicker than the larger sprocket, there are less rotations per minute, this is the same way a transmission's gears work, 1st gear is small, 5th gear is large. If you break it down, the wheels are actually gears in line with the transmission, if these gears are larger what are you going to get? Lower gearing ratios, this also affects your speedometer since it's configured for a specific wheel size.

So if a 15" wheel with 45 series rubber is the same diameter as a 17" wheel with 40 series rubber, which one is going to be quicker? Well, the diameter is identical, so you would have to look at the weights, if they weight of these wheels are identical there would be no difference in performance other than the more rigid sidewall would affect handling in a good way around the apex. And you would feel those potholes alot more.

So to answer your question...Does wheel weight really matter? Yes. Its the most important aspect of a wheel if you care about vehicle performance.

The more weight you take away from a wheel, the less the diameter matters, you could have 26" wheels that weigh 1 pound each and you'd be smoking the competition, unfortunately thats not the way it works in the real world, bigger wheels = more weight.

There is another way to counter additional wheel weight...that is to generate more engine power :)

bobdobbs
10-18-2003, 12:27 AM
Originally posted by eurosteez
So theroretically bodbo, we could condense this planet into oh...say a square inch? or even smaller? it could be condensed so much it went negative(blackhole)?

This planet? No. Too small.


But what does this have to do with you posting alot? [/B]
What do black holes have to do with wheel size?

chunky
10-19-2003, 09:03 PM
Originally posted by DownTheHatch
There's a simple experiment you can do that will prove to all of you the difference of weight vs. diameter.

If you have an office chair that rotates, give yourself a good push with your legs all the way out. Now gradually bring them closer to your body (the center of the rotating axis) as you spin. The speed at which you are spinning will increase as you pull your legs in, there is less rotational mass.


You can't reduce rotational mass except by reducing the mass that is rotating. So saying there is less rotational mass by pulling your legs in is a misnomer. What you are in fact doing is re-arranging the parameters that constitute angular momentum. Conservation of Angular Momentum for rotational systems that can change shape will lead you to the following conclusions: Moving the mass outwards results in a lower speed, but higher torque. Moving the mass inwards results in a higher speed, but lower torque. But in both cases, angular momentum is idential and thus the law of Conservation of Angular Momentum holds true.



Now, take something that weighs about 10 pounds and place it on your lap, infact, add as much weight as you want, getting yourself started will be increasingly tougher but once you're going, your legs will be determine how much freer you will spin.

Weight = Intertia (force holding an non-moving object in its place) You will notice this when you try to launch the car, say at the drag strip, with heavy wheels you will have a really hard time getting that car to go anywhere quickly, the same thing applies at highway speeds, when you goose the pedal you will not get as quick of a response if the wheels were lightweight. Kind of like the difference between throwing a bowling ball or throwing a basketball.

Diameter = Acceleration (rate at which an object gains speed)
If you've ever worked with gearing, the sizes always determine the speed at which the gear rotates, a smaller sprocket spins 2x or 3x quicker than the larger sprocket, there are less rotations per minute, this is the same way a transmission's gears work, 1st gear is small, 5th gear is large. If you break it down, the wheels are actually gears in line with the transmission, if these gears are larger what are you going to get? Lower gearing ratios, this also affects your speedometer since it's configured for a specific wheel size.

So if a 15" wheel with 45 series rubber is the same diameter as a 17" wheel with 40 series rubber, which one is going to be quicker? Well, the diameter is identical, so you would have to look at the weights, if they weight of these wheels are identical there would be no difference in performance other than the more rigid sidewall would affect handling in a good way around the apex. And you would feel those potholes alot more.

You still have to consider WHERE the weight is relative to the hub. If the weight is concentrated farther from the hub, you will need more torque to achieve the same angular speed. A 15" wheel will almost always have a center of mass that is closer to the hub.



So to answer your question...Does wheel weight really matter? Yes. Its the most important aspect of a wheel if you care about vehicle performance.

The more weight you take away from a wheel, the less the diameter matters, you could have 26" wheels that weigh 1 pound each and you'd be smoking the competition, unfortunately thats not the way it works in the real world, bigger wheels = more weight.

There is another way to counter additional wheel weight...that is to generate more engine power :)

More power makes up for a lot, but you still have to deal with forces that the suspension undergoes. The suspension has to work harder to control the motion of a heavier wheel. all the forces are linear, so the effect isn't as pronounced as the impact on acceleration, but the car will wander more over rough & uneven pavement with heavier wheels.

bobdobbs
10-19-2003, 09:13 PM
Originally posted by chunky
You still have to consider WHERE the weight is relative to the hub. If the weight is concentrated farther from the hub, you will need more torque to achieve the same angular speed.

Not only that, but the addtional torque required is a function of the distance from the center SQUARED.

glw
10-20-2003, 12:53 AM
IMO - the best tires weigh at least twice that of good wheels (15" to 17"). therefore, the diameter of the wheel (15" to 17") is probably not the most important part of the suspension picture - especially if you're still riding on the heavy stock struts and spinning the stock brake discs... the difference between fairly similar weighted 15" and 17" wheels will probably be indistinguishable.

for the average or beginning racer; get a light weight wheel that will allow you to fit the best tire for your purpose and you could compete with all but the most tricked out cars... your skill, tires, and other suspension components are more important than wheel diameter.

for the expert racer or person that can afford two sets of wheels and tires; of course a smaller and lighter wheel will be the best choice for absolute maximum performance. the rest of your car better be up to the task because your opponents few extra horsepower or a few other suspension mods might just make more of a difference than your smaller wheel diameter. and if your skills aren't up to the task, you will probably be beat by a more skilled driver on heavy larger equipment...


factoid
-------
although some say that larger wheels are better for appearance... 15" wheels are usually cheaper, lighter, and have better tire choices than 17" wheels.

tony speed
10-20-2003, 05:38 AM
let us not forget that there are two main reasons for bigger rims:
1) looks
2) fitting of a bigger brake kit

chunky
10-20-2003, 10:08 AM
Originally posted by tony speed
let us not forget that there are two main reasons for bigger rims:
1) looks
2) fitting of a bigger brake kit

#2 is mostly invalid. unless you're using 15" rotors on a civic, which is retarded in the first place considering the enzo uses 15" rotors. . .

eurosteez
10-20-2003, 10:54 PM
So you guys are sayin if you take the stock 18's off a porshe and put 15's on it will perform better???????????????????

just tryin to understand all this physics....:o ....:banana:

bobdobbs
10-20-2003, 11:10 PM
Originally posted by eurosteez
So you guys are sayin if you take the stock 18's off a porshe and put 15's on it will perform better???????????????????

The problem there is the GT3 has 295 tires in the back. Getting that width in 15" would be difficult.

eurosteez
10-20-2003, 11:16 PM
Lets say you could get 15 by 295's on there?

I don't totally understand all that physics that glw was talking about....and I don't know if it answers this question......but lets assume both tires have the same width, would an 18' have more area(grip) on the ground than a 15' with the same width. I'm just thinkin larger diameter=more area touching the ground.

bobdobbs
10-20-2003, 11:32 PM
Originally posted by eurosteez
Lets say you could get 15 by 295's on there?

I don't totally understand all that physics that glw was talking about....and I don't know if it answers this question......but lets assume both tires have the same width, would an 18' have more area(grip) on the ground than a 15' with the same width. I'm just thinkin larger diameter=more area touching the ground.

If they were the same width (295) and the 15" rims were the same width as the 18s, they would have the same amount of tread on the ground. If the 15" wheel is lighter, it will peform better, assuming no (performance) difference in tires.

Think of it this way: Your car is moving a weight around in a circle. The larger the circle (wheel/rim), the more work is required to move the weight, because the distance it travels is greater. If the circle thing throws you off, imagine pushing a heavy box down the street. With the larger wheel, you are essentially pushing the box FURTHER than you are with a smaller wheel. That requires more effort. That additional effort means your engine has to work harder.

chunky
10-21-2003, 07:34 AM
Originally posted by eurosteez
Lets say you could get 15 by 295's on there?

I don't totally understand all that physics that glw was talking about....and I don't know if it answers this question......but lets assume both tires have the same width, would an 18' have more area(grip) on the ground than a 15' with the same width. I'm just thinkin larger diameter=more area touching the ground.

You are correct if you are assuming that a larger OVERALL wheel AND tire diameter results in more contact patch. A larger overall wheel AND tire diameter makes the contact patch longer. Just making the wheel bigger while keeping the overall wheel and tire diameter the same has no impact on contact patch.

That is basically why you wouldn't put 18's on a porsche that came stock with them - b/c you NEED the larger overall wheel and tire diameter to get a big enough contact patch., aside from the fact that you'd need at least 17's to clear the monster brakes on a 911 turbo.

But if you look at the sidewall aspect ratios, a 295/40/18 series tire has an overall sidewall hieght of 118mm, a 225/50/15 series tire has an overall sidewall hieght of 112.5mm. So there is very small difference in sidewall hegiht between a bigger 18" wheel and a smaller 15" wheel.

BlasTech
10-21-2003, 08:43 AM
Originally posted by chunky
That is basically why you wouldn't put 18's on a porsche that came stock with them - b/c you NEED the larger overall wheel and tire diameter to get a big enough contact patch., aside from the fact that you'd need at least 17's to clear the monster brakes on a 911 turbo.

The wheels on new vehicles are getting out of hand, they're huge and its purely cosmetic with a sacrifice in performance. Wait till these folks go to buy new tires for thier cross-wagon and find out they're going to drop $1500-2000!

The only way to tell if the sidewalls are equal (because one is taller, and the shorter one has more diameter) is to either do the full area of the wheel/tire minus the area of the wheel. That will give you the square inches of rubber for each, then we can decide if 15" rubber weights more than low-profile 17" rubber... or we can to kuhmo's site and look at thier listed weights. ;)

eurosteez
10-21-2003, 12:55 PM
thanks chunk, that cleared up my confusion and answered my question. This thread is finally starting to make sense..LOL

tony speed
10-21-2003, 02:33 PM
Originally posted by chunky
#2 is mostly invalid. unless you're using 15" rotors on a civic, which is retarded in the first place considering the enzo uses 15" rotors. . .

i was thinking more about the actual brake/calipers

chunky
10-21-2003, 08:51 PM
Originally posted by tony speed
i was thinking more about the actual brake/calipers

if you're running 12 or 13" rotors, you can fit them inside a 16" wheel calipers and all with ease.

if you're running a 17" wheel, you can get get a 15" rotor before you start to run out of room for the calipers. . .

so using big brakes as an excuse to bling-i-fy your self is beat man. :D

I can dig that some people want to look good, and 17" wheels have a certain look to them, but please don't try and justify it as a performance oriented purchase on a civic.

You will never ever hear of a corvette owner increasing his rim size by 2" and then claiming that it's a performance mod. . . . same with porsche & ferrari owners. . . .

the rule is, the smallest wheel that will fit over the brakes that are suitable for your application.

rs_1101
10-21-2003, 11:28 PM
i just want to get the lightest set of 16's i can find. thats as bling as i need. id rather have the bang than the bling.

BlasTech
10-22-2003, 07:42 AM
Another piece of advise about buying wheels:

You usually boil it down to a couple of sets, and one is not as good as the other, but costs a little less.

Consider it a one-time purchase, and get the better ones. You wont ever "miss" the money, but if you get the less expensive ones, you'll always wonder if the others would be better, and might end up getting them anyway.

Also, ask the board here if you have found a good deal or not on what you picked. Despite our differences in tastes, we can all protect each other from getting ripped off.

;)

tony speed
10-23-2003, 01:44 PM
in that case....more bling for me :D

chunky
10-23-2003, 09:41 PM
Originally posted by tony speed
in that case....more bling for me :D

I have to admit, your bling does look good. :D

Vivid-Cruz
10-24-2003, 08:20 PM
ok..one last question for you guys (chunky, bobdobbs, etc..) .. if i were to purchase say 16-17lb 17" rims, wouldnt the performance be about equal to that of stock wheels? being that the overall weight would be reduced? im sure i could calculate this with some basic physics.. but i dont have all neccessary data..
thanks

chunky
10-25-2003, 09:45 PM
Originally posted by Vivid-Cruz
ok..one last question for you guys (chunky, bobdobbs, etc..) .. if i were to purchase say 16-17lb 17" rims, wouldnt the performance be about equal to that of stock wheels? being that the overall weight would be reduced? im sure i could calculate this with some basic physics.. but i dont have all neccessary data..
thanks

with lightweight 17" wheels, i doubt you'd loose any acceleration over stock wheels. stock wheels are HEAVY at 19lb each. a 12lb 17" wheel would reduce the impact of moving the weight of the tire outwards. and with a 12lb 16" wheel, i doubt if you'd notice any difference at all.

bobdobbs
10-25-2003, 11:00 PM
Originally posted by Vivid-Cruz
ok..one last question for you guys (chunky, bobdobbs, etc..) .. if i were to purchase say 16-17lb 17" rims, wouldnt the performance be about equal to that of stock wheels? being that the overall weight would be reduced? im sure i could calculate this with some basic physics.. but i dont have all neccessary data..
thanks
Chunky's right about acceleration, but there's a couple of other things to be concerned about: 1) Light-weight 17" wheels are going to be less sturdy and with a low-profile tire, you're going to bend a rim eventually and 2) the tallish sidewalls on your 15" tires make your ride more comfortable and you're going to feel a lot more bumps with low profile tires.

Consider 16" wheels.

ATRIOT
10-25-2003, 11:22 PM
Double negatives... Bobdobbs you slipping.:shockm:

bobdobbs
10-25-2003, 11:25 PM
Originally posted by ATRIOT
Double negatives... Bobdobbs you slipping.:shockm:
You got me, bro. I'd blame the three beers, but that's no excuse.

Vivid-Cruz
10-26-2003, 07:09 PM
Originally posted by bobdobbs
You got me, bro. I'd blame the three beers, but that's no excuse.

I cant find the double negative.. help me out..

alright thanks for the advice guys.. im prolly gonna drop it then throw some 16" wheels on there.. prolly take me a year to get that done... = (

bobdobbs
10-26-2003, 08:29 PM
Originally posted by Vivid-Cruz
I cant find the double negative.. help me out..

I hit the edit button and got rid of it.

rs_1101
10-26-2003, 08:45 PM
ohhh you trickay devil

stephen
10-27-2003, 03:12 PM
Originally posted by bobdobbs
Plus, they look far better than oversized tuner knockoff rims, IMHO.

15 inch superleggeras look sweet. Do you have a pic of chunky's car with the 225 width tyres?

chunky
10-27-2003, 05:12 PM
Originally posted by stephen
15 inch superleggeras look sweet. Do you have a pic of chunky's car with the 225 width tyres?

search the board, i have pics of them up on here somewhere. if you can't find 'em, i'll re-post them.

eurosteez
10-27-2003, 06:54 PM
I remember those pics.....aren't 15 x 225's pretty hard to find???

bobdobbs
10-27-2003, 08:24 PM
Here's mine (with 205s). Sorry about the kid. :D

stephen
10-28-2003, 06:58 AM
ok, i found it. I know a fair number of people have Superleggeras on their car. I wonder how many guys are running BBS rims...

http://www.hondalife.com/~chunky/estella.jpg