Tire Size Box

305/25R20 vs 305/35R20

305/35R20 compared with 305/25R20

+9.2% diameter, 0.0" width

305/35R20 is 28.41" tall vs 26.00". More than the 3% rule of thumb, so check carefully before switching.

26.0"20" rim3.0"12.0" wide
305/25R20 (solid) compared with 305/35R20 (dashed outline), drawn to scale

With 305/35R20 tires, when your speedometer says 60 mph you are really going

65.5 mph

305/35R20 is +2.40 inches (+9.2%) in overall diameter. That is more than the 3% most shops and makers recommend.

305/25R20305/35R20Difference%
Overall diameter26.00"28.41"+2.40"+9.2%
Section width12.01"12.01"0.00"0.0%
Sidewall height3.00"4.20"+1.20"+40.0%
Circumference81.69"89.24"+7.54"+9.2%
Revolutions per mile775.6710.0−65.6−8.5%

Speedometer difference

If your vehicle came with 305/25R20 and you fit 305/35R20, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph21.8 mph+1.8 mph
30 mph32.8 mph+2.8 mph
40 mph43.7 mph+3.7 mph
50 mph54.6 mph+4.6 mph
60 mph65.5 mph+5.5 mph
65 mph71.0 mph+6.0 mph
70 mph76.5 mph+6.5 mph
75 mph81.9 mph+6.9 mph
80 mph87.4 mph+7.4 mph

Each size on its own

Questions

Which is bigger, 305/25R20 or 305/35R20?
305/35R20 is taller by 2.40 inches (28.41" vs 26.00"). 305/25R20 is the same width.
Can I replace 305/25R20 with 305/35R20?
It is not recommended without checking carefully. The diameter difference is +9.2%, 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 305/35R20 change my speedometer?
When your speedometer reads 60 mph with 305/35R20 fitted (calibrated for 305/25R20), your real speed is 65.5 mph. Your odometer will under-count miles by about 9.2%.
Will 305/35R20 lift my vehicle?
Ride height changes by half the diameter difference: +1.20 inches of ground clearance at the axle.

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