Tire Size Box

315/35R22 vs 305/40R22

305/40R22 compared with 315/35R22

+3.0% diameter, −0.4" width

305/40R22 is 31.61" tall vs 30.68". More than the 3% rule of thumb, so check carefully before switching.

30.7"22" rim4.3"12.4" wide
315/35R22 (solid) compared with 305/40R22 (dashed outline), drawn to scale

With 305/40R22 tires, when your speedometer says 60 mph you are really going

61.8 mph

305/40R22 is +0.93 inches (+3.0%) in overall diameter. That is more than the 3% most shops and makers recommend.

315/35R22305/40R22Difference%
Overall diameter30.68"31.61"+0.93"+3.0%
Section width12.40"12.01"−0.39"−3.2%
Sidewall height4.34"4.80"+0.46"+10.7%
Circumference96.39"99.29"+2.91"+3.0%
Revolutions per mile657.3638.1−19.2−2.9%

Speedometer difference

If your vehicle came with 315/35R22 and you fit 305/40R22, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph20.6 mph+0.6 mph
30 mph30.9 mph+0.9 mph
40 mph41.2 mph+1.2 mph
50 mph51.5 mph+1.5 mph
60 mph61.8 mph+1.8 mph
65 mph67.0 mph+2.0 mph
70 mph72.1 mph+2.1 mph
75 mph77.3 mph+2.3 mph
80 mph82.4 mph+2.4 mph

Each size on its own

Questions

Which is bigger, 315/35R22 or 305/40R22?
305/40R22 is taller by 0.93 inches (31.61" vs 30.68"). 315/35R22 is wider by 0.39 inches.
Can I replace 315/35R22 with 305/40R22?
It is not recommended without checking carefully. The diameter difference is +3.0%, 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 305/40R22 change my speedometer?
When your speedometer reads 60 mph with 305/40R22 fitted (calibrated for 315/35R22), your real speed is 61.8 mph. Your odometer will under-count miles by about 3.0%.
Will 305/40R22 lift my vehicle?
Ride height changes by half the diameter difference: +0.46 inches of ground clearance at the axle.

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