Tire Size Box

235/80R15 vs 235/85R15

235/85R15 compared with 235/80R15

+3.1% diameter, 0.0" width

235/85R15 is 30.73" tall vs 29.80". More than the 3% rule of thumb, so check carefully before switching.

29.8"15" rim7.4"9.3" wide
235/80R15 (solid) compared with 235/85R15 (dashed outline), drawn to scale

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

61.9 mph

235/85R15 is +0.93 inches (+3.1%) in overall diameter. That is more than the 3% most shops and makers recommend.

235/80R15235/85R15Difference%
Overall diameter29.80"30.73"+0.93"+3.1%
Section width9.25"9.25"0.00"0.0%
Sidewall height7.40"7.86"+0.46"+6.3%
Circumference93.63"96.54"+2.91"+3.1%
Revolutions per mile676.7656.3−20.4−3.0%

Speedometer difference

If your vehicle came with 235/80R15 and you fit 235/85R15, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph20.6 mph+0.6 mph
30 mph30.9 mph+0.9 mph
40 mph41.2 mph+1.2 mph
50 mph51.6 mph+1.6 mph
60 mph61.9 mph+1.9 mph
65 mph67.0 mph+2.0 mph
70 mph72.2 mph+2.2 mph
75 mph77.3 mph+2.3 mph
80 mph82.5 mph+2.5 mph

Each size on its own

Questions

Which is bigger, 235/80R15 or 235/85R15?
235/85R15 is taller by 0.93 inches (30.73" vs 29.80"). 235/80R15 is the same width.
Can I replace 235/80R15 with 235/85R15?
It is not recommended without checking carefully. The diameter difference is +3.1%, 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 235/80R15), your real speed is 61.9 mph. Your odometer will under-count miles by about 3.1%.
Will 235/85R15 lift my vehicle?
Ride height changes by half the diameter difference: +0.46 inches of ground clearance at the axle.

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