I was interested in putting a larger wheel on my 95 900s convertible. I did some calculations with info from the tire rack site and the wheels and tires I am considering would give me an extra inch in diameter. Does anyone have any experience as to how much this increase would affect my speedometer and final drive ratio? Thanks in advance for any assistance!
wheels on 900s
Mar 06, 2004
1 Replies
The answer to your question is a simple equation:
Indicated Speed Change as a % = Change in size / Present size * 100
Tire Rack indicates your car was originally equiped with Michelin MXV4 in
195/60VR15 size. These tires have a diameter of 24.2", so (1 / 24.2) *100 = 4.13%Also, in case you didn't realize, the indicated speed on the speedo will
*decrease* with an increase in tire diameter, as will the overall final drive ratio, resulting in the calculated decrease in engine rpm at any particular speed.-Fred W
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