larger wheels...how fast am i going?

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25rsfun
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larger wheels...how fast am i going?

Post by 25rsfun » Tue Feb 27, 2007 12:38 am

i put on some 18'' wheels on my rs and i wanted to know if anyone knew the conversion is for the spedometer with the plus size wheels, and if there is anywhere around to get it calibrated.

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Cereb Daithi
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Post by Cereb Daithi » Tue Feb 27, 2007 1:19 am

bigger wheel = your speedo will read lower than what your actual speed is. I'd think about 5-10mph low. lol i know places up here to get it done but that does you no good

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WRXWagon2112
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Post by WRXWagon2112 » Tue Feb 27, 2007 7:45 am

I think this also depends on the size of the tire that you're using. If you go up a rim size but get lower profile tires, the overall diameter is essentially the same and you see little to no error in your speedometer. What size tires did you have before and what size are on the 18's now?

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Post by moxnix » Tue Feb 27, 2007 8:25 am

Try the Miata.net tire calculator.

http://www.miata.net/garage/tirecalc.html

Put in your stock tire size and then the new tire size and it will give you the % you are off.

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drwrx
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Post by drwrx » Tue Feb 27, 2007 12:24 pm

Those conversions are decent, but they are by no means exact.
Every tire from each manufacturer will have it's own dimensional differences.

For example the diameter of a Bridgestone RE92 205/55 16 is 24.8" and does 837 revs per mile. A Yokohama ES 100 205/55 16 is 25.1" and does 828 revs per mile. The RE 92 also has 11/32" tread depth while the ES 100 only has 9/32." The ES 100 tread width is also 7.5" as opposed to the RE92's tread width of 6.2" while the tread width difference won't throw off your speedo, an extra 1.3" of contact patch pays off in dry traction on the road.

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Re: larger wheels...how fast am i going?

Post by Libra Monkee » Tue Feb 27, 2007 1:14 pm

25rsfun wrote:...if there is anywhere around to get it calibrated.


I know there was I place I went near Fairfax Circle last year after one of my speeding tickets. :drive: Can't remember what the name of was though.
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zaxrex
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Post by zaxrex » Tue Feb 27, 2007 1:35 pm

Keep it like it is and just go slower. if you ever get pulled for speeding, then you can go and get the error calibrated, go back to court and just get improper equipment ticket instead of speeding.
:lol:
Or not.
Patience is the ability to idle your motor when you feel like stripping your gears

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drwrx
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Post by drwrx » Tue Feb 27, 2007 3:03 pm

The easiest way is to check the diameter of the "stock" tire vs. the 18" tire that you are replacing it with. If your stock tires were 205/55 16 you know the diameter should be around 25" so go with a 225/40 18 tire which average right around 25" in diameter. That would keep your speedo calibration on target.

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