Tire Size Box

235/75R15 vs 235/85R15

235/85R15 compared with 235/75R15

+6.4% diameter, 0.0" width

235/85R15 is 30.73" tall vs 28.88". More than the 3% rule of thumb, so check carefully before switching.

28.9"15" rim6.9"9.3" wide
235/75R15 (solid) compared with 235/85R15 (dashed outline), drawn to scale

With 235/85R15 tires, when your speedometer says 60 mph you are really going

63.8 mph

235/85R15 is +1.85 inches (+6.4%) in overall diameter. That is more than the 3% most shops and makers recommend.

235/75R15235/85R15Difference%
Overall diameter28.88"30.73"+1.85"+6.4%
Section width9.25"9.25"0.00"0.0%
Sidewall height6.94"7.86"+0.93"+13.3%
Circumference90.72"96.54"+5.81"+6.4%
Revolutions per mile698.4656.3−42.1−6.0%

Speedometer difference

If your vehicle came with 235/75R15 and you fit 235/85R15, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph21.3 mph+1.3 mph
30 mph31.9 mph+1.9 mph
40 mph42.6 mph+2.6 mph
50 mph53.2 mph+3.2 mph
60 mph63.8 mph+3.8 mph
65 mph69.2 mph+4.2 mph
70 mph74.5 mph+4.5 mph
75 mph79.8 mph+4.8 mph
80 mph85.1 mph+5.1 mph

Each size on its own

Questions

Which is bigger, 235/75R15 or 235/85R15?
235/85R15 is taller by 1.85 inches (30.73" vs 28.88"). 235/75R15 is the same width.
Can I replace 235/75R15 with 235/85R15?
It is not recommended without checking carefully. The diameter difference is +6.4%, more than the 3% most shops and makers allow. It will throw off the speedometer and may affect ABS, stability control and clearance.
How much will 235/85R15 change my speedometer?
When your speedometer reads 60 mph with 235/85R15 fitted (calibrated for 235/75R15), your real speed is 63.8 mph. Your odometer will under-count miles by about 6.4%.
Will 235/85R15 lift my vehicle?
Ride height changes by half the diameter difference: +0.93 inches of ground clearance at the axle.

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