Recalibration for 18's

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03-20-2003 | 05:39 PM

EEnjai

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Recalibration for 18's

I recently put 18's on my WRX and I just was wondering what you guys (and girls) think about recalibrating the tach? Do you think the 18's will have a big effect on, especially, the speed?

- nick

03-20-2003 | 05:46 PM

Cabal

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This will depend entirely on the size of the tire. You can buy 17s and 18s that will not change the rotation speed of the wheels. I don't recall the correct size for 18s, but 17s should be 215/45 - 17. Most tire sales sites will have a calculator you can use.

03-20-2003 | 05:52 PM

Mulder

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Joined: Nov 2002

Posts: 1,646

From: NYC

Car Info: 02 WRX WRB

Here's one you can use-
http://www.miata.net/garage/tirecalc.html

A proper "plus 1", "plus 2", or "plus 0" tire/wheel upgrade will maintain the same diameter and rolling circumference as the stock wheels, within a percent or two.

There is no recalibration possible, the ECU gets an input from the speed sensor with a certain number of pulses per mile that is based on the stock wheel size.

03-24-2003 | 06:02 PM

EEnjai

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Thanks a lot, I talked with some tuners who I work with occasionally and they basically came to the same consensus about not being able to recalibrate as you guys. With the tires I have on though, it will be no problem.

- nick

03-24-2003 | 06:37 PM

awns729

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Posts: 4,568

From: Rockland County...NY

Car Info: want a WRX

The stock WRX tires are 205/55 R16 right? The BBS 17' wheels on the STi are 225/45 ZR17. I used the calculator and it said the speedometer on a car with the STi wheels/tires (that previously had stock WRX wheels/tires) would be .4% too slow. Is this right?(Do I even make sense?)

Thanx
Are the BBS wheels that are an option with the WRX 225/45?

03-25-2003 | 06:58 AM

C-WReX

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Your calculations appear to me to be correct. Tirerack says the stock option 17s are 215/45/17; that's what I went with on the 17X7s that I ordered. The 215s would have a reading of 1.0% too fast, which is a miniscule change. Of course, so is "0.4% too slow". Close enough.