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      10-20-2012, 10:30 AM   #1
135iDCT
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Why smaller wheels...?

Why smaller wheels like 17" or less in better for track and 1/4 mile ?

If i want to go from 18 to 17 do i need to reprogramme the car ??

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      10-23-2012, 09:59 PM   #2
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My understanding is that the smaller the rim, the larger and softer you can go with the sidewall. Increased compliance in the sidewall will help with launching in the 1/4 mile. Also, smaller wheels tend to be lighter and therefore may reduce your unsprung weight.

For the track though, you usually want stiffer sidewalls for improved steering response.

As for the second question, it depends on your tire circumference rather than rim diameter as to whether you will or will not need to recalibrate your speedo. I highly doubt you would need to reprogram the car.

Basically, if you downsize to a 17 but you increase the sidewall height to the equivalent or close to it you shouldn't notice any difference in speed shown and actual speed travelled. But if you downsize and keep the same sidewall height then your tyre circumference will be smaller and thus you will be travelling slower than your actual speedo read out.
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      10-24-2012, 12:37 PM   #3
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Quote:
Originally Posted by froop View Post
My understanding is that the smaller the rim, the larger and softer you can go with the sidewall. Increased compliance in the sidewall will help with launching in the 1/4 mile. Also, smaller wheels tend to be lighter and therefore may reduce your unsprung weight.

For the track though, you usually want stiffer sidewalls for improved steering response.

As for the second question, it depends on your tire circumference rather than rim diameter as to whether you will or will not need to recalibrate your speedo. I highly doubt you would need to reprogram the car.

Basically, if you downsize to a 17 but you increase the sidewall height to the equivalent or close to it you shouldn't notice any difference in speed shown and actual speed travelled. But if you downsize and keep the same sidewall height then your tyre circumference will be smaller and thus you will be travelling slower than your actual speedo read out.
Thnx alot very helpful
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      10-24-2012, 04:55 PM   #4
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I agree with what was said. The weight of the wheels, tires, brakes, etc is unsprung. It's connected directly to the ground without your springs and shocks acting as a mediator. Also, the wheels and tires are spinning and have a certain inertia to their spin, which is directly related to their weight/mass. The motor will have to work harder to overcome that inertia whenever you want to change your speed, and this will be easier to do with lighter wheels/tires. You want your wheels and tires to be as light as possible for the best performance, but need bigger wheels to clear the brakes, and wider wheels to put as much rubber to the ground as possible. Unless you're going for looks, the smallest possible diameter wheel that you can fit over the brakes, with the widest possible width to give you more traction would be ideal.

As froop said, if you go with a 17" wheel versus an 18", you're likely going to end up with a 17" wheel with a slightly taller tire, and it will end up being the same overall size as an 18" wheel with a thinner-profile tire. In this case, your speedo won't be off more than like 1%, and it's already off by something like 3-5% anyway so you won't notice.
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