Tire Size Box

245/75R15 vs 245/85R15

245/85R15 compared with 245/75R15

+6.5% diameter, 0.0" width

245/85R15 is 31.40" tall vs 29.47". More than the 3% rule of thumb, so check carefully before switching.

29.5"15" rim7.2"9.6" wide
245/75R15 (solid) compared with 245/85R15 (dashed outline), drawn to scale

With 245/85R15 tires, when your speedometer says 60 mph you are really going

63.9 mph

245/85R15 is +1.93 inches (+6.5%) in overall diameter. That is more than the 3% most shops and makers recommend.

245/75R15245/85R15Difference%
Overall diameter29.47"31.40"+1.93"+6.5%
Section width9.65"9.65"0.00"0.0%
Sidewall height7.23"8.20"+0.96"+13.3%
Circumference92.58"98.64"+6.06"+6.5%
Revolutions per mile684.4642.3−42.1−6.1%

Speedometer difference

If your vehicle came with 245/75R15 and you fit 245/85R15, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph21.3 mph+1.3 mph
30 mph32.0 mph+2.0 mph
40 mph42.6 mph+2.6 mph
50 mph53.3 mph+3.3 mph
60 mph63.9 mph+3.9 mph
65 mph69.3 mph+4.3 mph
70 mph74.6 mph+4.6 mph
75 mph79.9 mph+4.9 mph
80 mph85.2 mph+5.2 mph

Each size on its own

Questions

Which is bigger, 245/75R15 or 245/85R15?
245/85R15 is taller by 1.93 inches (31.40" vs 29.47"). 245/75R15 is the same width.
Can I replace 245/75R15 with 245/85R15?
It is not recommended without checking carefully. The diameter difference is +6.5%, 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 245/85R15 change my speedometer?
When your speedometer reads 60 mph with 245/85R15 fitted (calibrated for 245/75R15), your real speed is 63.9 mph. Your odometer will under-count miles by about 6.5%.
Will 245/85R15 lift my vehicle?
Ride height changes by half the diameter difference: +0.96 inches of ground clearance at the axle.

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