Re: What will happen when I change 235/75R15s for 215/75R15s?


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Posted by TerryA on February 11, 1999 at 22:39:07:

In Reply to: What will happen when I change 235/75R15s for 215/75R15s? posted by Tie on February 10, 1999 at 00:01:10:

I use a microsoft excel spreadsheet to calc the changes. Here is the first one. If you would like, I will send it to you. It has options for gear ratio to see what change in the speedo with occur.

From
Tread Width (mm.) 235 Tread Width (mm.) 215
Sidewall Ratio 75 Sidewall Ratio 75
Rim Diameter (in.) 15 Rim Diameter (in.) 15

Tire Diameter (mm.) 733.50 Tire Diameter (mm.) 703.50
Tire Diameter (in.) 28.88 Tire Diameter (in.) 27.70
Sidewall Height (mm.) 176.25 Sidewall Height (mm.) 161.25
Sidewall Height (in.) 6.94 Sidewall Height (in.) 6.35
Tread Width (in.) 9.25 Tread Width (in.) 8.46
Tire RPM @60 mph 698.49 Tire RPM @60 mph 728.27
Difference Ratio -4.09% (smaller)

The second one is:
Tread Width (mm.) 235 Tread Width (mm.) 225
Sidewall Ratio 75 Sidewall Ratio 70
Rim Diameter (in.) 15 Rim Diameter (in.) 15

Tire Diameter (mm.) 733.50 Tire Diameter (mm.) 696.00
Tire Diameter (in.) 28.88 Tire Diameter (in.) 27.40
Sidewall Height (mm.) 176.25 Sidewall Height (mm.) 157.50
Sidewall Height (in.) 6.94 Sidewall Height (in.) 6.20
Tread Width (in.) 9.25 Tread Width (in.) 8.86
Tire RPM @60 mph 698.49 Tire RPM @60 mph 736.12

Difference Ratio -5.11% (even smaller)

Note both of these will change your speedometer slightly. It may show 60 mph but you may be actually going 62 mph.

Enjoy


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