Tire Size Box

315/25R20 vs 315/35R20

315/35R20 compared with 315/25R20

+9.5% diameter, 0.0" width

315/35R20 is 28.68" tall vs 26.20". More than the 3% rule of thumb, so check carefully before switching.

26.2"20" rim3.1"12.4" wide
315/25R20 (solid) compared with 315/35R20 (dashed outline), drawn to scale

With 315/35R20 tires, when your speedometer says 60 mph you are really going

65.7 mph

315/35R20 is +2.48 inches (+9.5%) in overall diameter. That is more than the 3% most shops and makers recommend.

315/25R20315/35R20Difference%
Overall diameter26.20"28.68"+2.48"+9.5%
Section width12.40"12.40"0.00"0.0%
Sidewall height3.10"4.34"+1.24"+40.0%
Circumference82.31"90.10"+7.79"+9.5%
Revolutions per mile769.8703.2−66.6−8.6%

Speedometer difference

If your vehicle came with 315/25R20 and you fit 315/35R20, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph21.9 mph+1.9 mph
30 mph32.8 mph+2.8 mph
40 mph43.8 mph+3.8 mph
50 mph54.7 mph+4.7 mph
60 mph65.7 mph+5.7 mph
65 mph71.2 mph+6.2 mph
70 mph76.6 mph+6.6 mph
75 mph82.1 mph+7.1 mph
80 mph87.6 mph+7.6 mph

Each size on its own

Questions

Which is bigger, 315/25R20 or 315/35R20?
315/35R20 is taller by 2.48 inches (28.68" vs 26.20"). 315/25R20 is the same width.
Can I replace 315/25R20 with 315/35R20?
It is not recommended without checking carefully. The diameter difference is +9.5%, 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 315/35R20 change my speedometer?
When your speedometer reads 60 mph with 315/35R20 fitted (calibrated for 315/25R20), your real speed is 65.7 mph. Your odometer will under-count miles by about 9.5%.
Will 315/35R20 lift my vehicle?
Ride height changes by half the diameter difference: +1.24 inches of ground clearance at the axle.

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