Tire Size Box

235/80R13 vs 235/85R13

235/85R13 compared with 235/80R13

+3.3% diameter, 0.0" width

235/85R13 is 28.73" tall vs 27.80". More than the 3% rule of thumb, so check carefully before switching.

27.8"13" rim7.4"9.3" wide
235/80R13 (solid) compared with 235/85R13 (dashed outline), drawn to scale

With 235/85R13 tires, when your speedometer says 60 mph you are really going

62.0 mph

235/85R13 is +0.93 inches (+3.3%) in overall diameter. That is more than the 3% most shops and makers recommend.

235/80R13235/85R13Difference%
Overall diameter27.80"28.73"+0.93"+3.3%
Section width9.25"9.25"0.00"0.0%
Sidewall height7.40"7.86"+0.46"+6.3%
Circumference87.35"90.25"+2.91"+3.3%
Revolutions per mile725.4702.0−23.4−3.2%

Speedometer difference

If your vehicle came with 235/80R13 and you fit 235/85R13, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph20.7 mph+0.7 mph
30 mph31.0 mph+1.0 mph
40 mph41.3 mph+1.3 mph
50 mph51.7 mph+1.7 mph
60 mph62.0 mph+2.0 mph
65 mph67.2 mph+2.2 mph
70 mph72.3 mph+2.3 mph
75 mph77.5 mph+2.5 mph
80 mph82.7 mph+2.7 mph

Each size on its own

Questions

Which is bigger, 235/80R13 or 235/85R13?
235/85R13 is taller by 0.93 inches (28.73" vs 27.80"). 235/80R13 is the same width.
Can I replace 235/80R13 with 235/85R13?
It is not recommended without checking carefully. The diameter difference is +3.3%, 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 235/85R13 change my speedometer?
When your speedometer reads 60 mph with 235/85R13 fitted (calibrated for 235/80R13), your real speed is 62.0 mph. Your odometer will under-count miles by about 3.3%.
Will 235/85R13 lift my vehicle?
Ride height changes by half the diameter difference: +0.46 inches of ground clearance at the axle.

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