Tire Size Box

315/30R20 vs 315/35R20

315/35R20 compared with 315/30R20

+4.5% diameter, 0.0" width

315/35R20 is 28.68" tall vs 27.44". More than the 3% rule of thumb, so check carefully before switching.

27.4"20" rim3.7"12.4" wide
315/30R20 (solid) compared with 315/35R20 (dashed outline), drawn to scale

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

62.7 mph

315/35R20 is +1.24 inches (+4.5%) in overall diameter. That is more than the 3% most shops and makers recommend.

315/30R20315/35R20Difference%
Overall diameter27.44"28.68"+1.24"+4.5%
Section width12.40"12.40"0.00"0.0%
Sidewall height3.72"4.34"+0.62"+16.7%
Circumference86.21"90.10"+3.90"+4.5%
Revolutions per mile735.0703.2−31.8−4.3%

Speedometer difference

If your vehicle came with 315/30R20 and you fit 315/35R20, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph20.9 mph+0.9 mph
30 mph31.4 mph+1.4 mph
40 mph41.8 mph+1.8 mph
50 mph52.3 mph+2.3 mph
60 mph62.7 mph+2.7 mph
65 mph67.9 mph+2.9 mph
70 mph73.2 mph+3.2 mph
75 mph78.4 mph+3.4 mph
80 mph83.6 mph+3.6 mph

Each size on its own

Questions

Which is bigger, 315/30R20 or 315/35R20?
315/35R20 is taller by 1.24 inches (28.68" vs 27.44"). 315/30R20 is the same width.
Can I replace 315/30R20 with 315/35R20?
It is not recommended without checking carefully. The diameter difference is +4.5%, 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 315/30R20), your real speed is 62.7 mph. Your odometer will under-count miles by about 4.5%.
Will 315/35R20 lift my vehicle?
Ride height changes by half the diameter difference: +0.62 inches of ground clearance at the axle.

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