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Discussion Starter · #1 ·
I have a 1994 Caprice 9C1, and really like the certified digital spedo, and I have been thinking about changing tires size's from 235/70/15's to some 225/60/15's. I'm looking for some better traction and some better handling, but my question is, how much will my spedo be off before I get my computer reprogrammed? This is just a future mod that I'm planning on doing and I'm trying to do all my research. And while I'm asking, what's the "biggest" widest tire I can get on my car?? It has the stock 15x7 ralley wheel's. Thanks


Discussion Starter · #2 ·
225/60-15 is NOT a plus 1 (+1) size up from 235/70-15, in fact it is a smaller tire in every category. See the following chart:

Tire Size ------ 235/70-15 / 225/60-15
Overall Diameter --- 27.95 / 25.63
Tread Width --------- 9.25 / 8.86
Sidewall Height ----- 6.48 / 5.31
Speedometer Reading - 55.0 / 60.0
Diameter Ratio ---------- 91.7%
Tread Width Ratio ------- 95.7%

In order to go to a 60 series tire with NO reprogramming of your computer, you would need a 275/60-15 and that would not fit on your rim. You really need to increase the diameter of your wheel in order to better your handling. There are much better tires available in the 16 inch and up rim sizes. If you want to maintain your stock wheels, Chief Terry Fiene [email protected] can give you the best advice on stock (9C1) performance tires.

Howard Rothstein
1996 BBB Signature Series
Impala SS Club of America #147 - Board of Directors
SEIL - Vice President
NAISSO - Life Member #1907
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Discussion Starter · #4 ·
Does this only effect digital speedos? (sorry if this is a moronic question)

Discussion Starter · #5 ·

The speedo, whether digital or analog, should give you the correct speed for the wheels & tires for which it was calibrated.

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