What size tires best for stock rims

[SiRman]

What size tires are you guys putting on who are running stock rims?
Wondering if anyone is running different sizes, or are you sticking to stock size.

[Peking]

I would say stay stock size if those are your daily wheels. If not than getting something of a different size will not be bad. I was planning on those Neo Gens when the rubber runs out on mine.

[SiRman]

Thinking about getting Yoko es100's for the stock rims for the summer.
Plan on doing at least one track day.

[Peking]

Yeah I like those too.

[Eee Pee]

An upgrade (if you aren't concerned with an accurate speedo and possibly the tach) would be a 205/50/15.
A hair wider, almost an inch shorter.
Which is going to get the car lower, and help in the gearing, etc.


Yokohama AVS ES100 as an example

195/60HR15

7.9" section width
6.8" tread width
24.2" diameter
858 rpm

205/50VR15

8.2" section width
7.5" tread width
23.2" diameter
894 rpm

I'd like to thank Tirerack for their contribution to this thread...

[SiRman]

and help in the gearing

Interesting point about the gearing, would it be a noticeable diff?
Anyone else have any comments on this.
Would it be worth the slightly wider tire and gear diff. even though the speedo would be a little off?

[Zero Three Si]

Originally posted by SiRman
Interesting point about the gearing, would it be a noticeable diff?
Anyone else have any comments on this.
Would it be worth the slightly wider tire and gear diff. even though the speedo would be a little off?

Wider tire=more tire in contact with the road=better cornering

1 inch closer to the ground=lower center of gravity=better cornering

I wonder if those tires would make more road noise though?

[SiRman]

Ok let me run this by you guys then.

If I change the overal diameter of the tires from 24.2(858 revs per mile) to 23.2 (894 revs per mile)

THis will effect my final drive ratio by a factor of 894/858 = 1.042

So the resulting final drive will be 1.042 x 4.764 = final ratio of 4.964.

Correct me if I'm wrong here.

[STP03BlueSI]

Originally posted by SiRman
Ok let me run this by you guys then.

If I change the overal diameter of the tires from 24.2(858 revs per mile) to 23.2 (894 revs per mile)

THis will effect my final drive ratio by a factor of 894/858 = 1.042

So the resulting final drive will be 1.042 x 4.764 = final ratio of 4.964.

Correct me if I'm wrong here.

I think you are correct.:)

[SiRman]

Final ratio of 4.964 = me:smilem:

I think I will go this way.

[Eee Pee]

Actually, it will only be a half an inch closer to the ground, but hey, at least it's closer to the ground.

:smilem: <--- that's hilarious.

[SiRman]

<--- that's hilarious.

You do know about the monkeys right?

Click on "get more" below the emoticons and go back to the oldschool days of ephatch.:shadesm: :banana:

[myeverlovinsir]

Originally posted by SiRman
Ok let me run this by you guys then.

If I change the overal diameter of the tires from 24.2(858 revs per mile) to 23.2 (894 revs per mile)

THis will effect my final drive ratio by a factor of 894/858 = 1.042

So the resulting final drive will be 1.042 x 4.764 = final ratio of 4.964.

Correct me if I'm wrong here.

I found that by decreasing the overall diameter of your tire actually decreases the final drive. Using your number of 23.2 your final drive would be 4.5671

You had it but just divided wrong. Just take the tire diameter (new one) / Stock tire diameter --> 23.2/24.2 = 0.958677 then multiply that by the stock final drive.

Use this link to try it for yourself---> LINK

Scroll down till you see this title:
RPM, MPH, Tire Diameter and Final Drive Ratio v. 1.0

This calculator derives RPM, MPH, tire diameter and final drive ratio. When any three parameters are entered the fourth one is calculated.

There are numerous other neat tools there as well. Enjoy:D

[SiRman]

I followed the link.
Doesn't seem quite right

By reducing the tire size, you get the same effect as if you increased the final drive #:

Lets say your tire has a circumfrence of 100cm. So for every revolution at the trans output the car rolls 100cm.

Now change the tire circumference to 50cm. Now for every rev. at the output of the trans. The car only rolls 50cm.

To travel the same distance in the same amount of time with the 50cm tires the output of the trans must spin twice as many revs.

If you increase the final drive ratio (inverse of actual output gearsize) you now have to spin the motor more for a given ground speed, which is the same effect as smaller tires.

I know you know all this myeverlovinsir, just trying to work through this brain teaser. Final gear ratios are kind of wacky becasue of the fact that a smaller
gear on one end of a set makes a bigger ratio.While a bigger gear on the other end makes a smaller ratio.

[myeverlovinsir]

Here is the formula used to calculate Gear Ratio:

Gear Ratio = RPM x Tire Diameter / MPH x 336

Assuming that the RPM and MPH are constant, when you increase the tire diameter the gear ratio goes up and decreases when the tire diameter goes down.

Here is the formula used to calculate RPM:

RPM = Gear Ratio x MPH x 336 / Tire Diameter

Here you can see that by increasing the tire diameter it has the opposite effect on RPM...it decreases, and vice versa.

The Gear Ratio is defined as the number of times the driveshaft (or pinion) will rotate for each turn of the wheel (or ring gear). So if you were to have a 4.56:1 gear ratio the driveshaft would turn 4.56 times for every turn of the wheel.

Similarily, gear ratio is calculated by dividing the number of teeth on the ring gear by the number of teeth on the pinion gear. The higher the number, the lower the ratio: a 4.76 gear has a lower ratio than a 4.05 gear.

As you know, whenever you change tire sizes you affect the final drive ratio. Switching from a 24.2" tire to a 23.2" tire changes the the final drive ratio by 1%. This is no big deal, however say switching from a 24.2" tire to a 28.2" tire changes the final drive ratio by 14% and may drop the engine out of its' "power band" and result in poor performance and fuel economy. You could change the final gear ratio to compensate for the change in tire size. If we originally had a gear ratio of 4.764 then to restore the stock performance we need to choose a gear ratio that is close to 14% lower, such as 5.43:1

This is just an example but hope that helps.;)