Tire Size Box

245/70R15 vs 245/80R15

245/80R15 compared with 245/70R15

+6.8% diameter, 0.0" width

245/80R15 is 30.43" tall vs 28.50". More than the 3% rule of thumb, so check carefully before switching.

28.5"15" rim6.8"9.6" wide
245/70R15 (solid) compared with 245/80R15 (dashed outline), drawn to scale

With 245/80R15 tires, when your speedometer says 60 mph you are really going

64.1 mph

245/80R15 is +1.93 inches (+6.8%) in overall diameter. That is more than the 3% most shops and makers recommend.

245/70R15245/80R15Difference%
Overall diameter28.50"30.43"+1.93"+6.8%
Section width9.65"9.65"0.00"0.0%
Sidewall height6.75"7.72"+0.96"+14.3%
Circumference89.55"95.61"+6.06"+6.8%
Revolutions per mile707.6662.7−44.9−6.3%

Speedometer difference

If your vehicle came with 245/70R15 and you fit 245/80R15, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph21.4 mph+1.4 mph
30 mph32.0 mph+2.0 mph
40 mph42.7 mph+2.7 mph
50 mph53.4 mph+3.4 mph
60 mph64.1 mph+4.1 mph
65 mph69.4 mph+4.4 mph
70 mph74.7 mph+4.7 mph
75 mph80.1 mph+5.1 mph
80 mph85.4 mph+5.4 mph

Each size on its own

Questions

Which is bigger, 245/70R15 or 245/80R15?
245/80R15 is taller by 1.93 inches (30.43" vs 28.50"). 245/70R15 is the same width.
Can I replace 245/70R15 with 245/80R15?
It is not recommended without checking carefully. The diameter difference is +6.8%, 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 245/80R15 change my speedometer?
When your speedometer reads 60 mph with 245/80R15 fitted (calibrated for 245/70R15), your real speed is 64.1 mph. Your odometer will under-count miles by about 6.8%.
Will 245/80R15 lift my vehicle?
Ride height changes by half the diameter difference: +0.96 inches of ground clearance at the axle.

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