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...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.
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...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:
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.
Last edited by glw; 10-14-2003 at 11:20 PM.
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.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...
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.
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?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.
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.
bobdobbs and chunky,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.
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 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.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.
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.225/50/15 is the ideal size for performance.
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.
Last edited by glw; 10-15-2003 at 02:41 AM.
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 :)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.
You're missing the point, The MAIN CONTRIBUTING FACTOR TO THE LOWER LAP TIMES OF THE 17" WHEEL IS DUE TO THE INCREASED WIDTH.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 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.
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.
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.
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.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.
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.
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.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.
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.
Last edited by bobdobbs; 10-15-2003 at 01:42 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.
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
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. :)
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