Tire Size Box

305/35R22 vs 305/40R22

305/40R22 compared with 305/35R22

+3.9% diameter, 0.0" width

305/40R22 is 31.61" tall vs 30.41". More than the 3% rule of thumb, so check carefully before switching.

30.4"22" rim4.2"12.0" wide
305/35R22 (solid) compared with 305/40R22 (dashed outline), drawn to scale

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

62.4 mph

305/40R22 is +1.20 inches (+3.9%) in overall diameter. That is more than the 3% most shops and makers recommend.

305/35R22305/40R22Difference%
Overall diameter30.41"31.61"+1.20"+3.9%
Section width12.01"12.01"0.00"0.0%
Sidewall height4.20"4.80"+0.60"+14.3%
Circumference95.52"99.29"+3.77"+3.9%
Revolutions per mile663.3638.1−25.2−3.8%

Speedometer difference

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

Speedometer showsActual speedDifference
20 mph20.8 mph+0.8 mph
30 mph31.2 mph+1.2 mph
40 mph41.6 mph+1.6 mph
50 mph52.0 mph+2.0 mph
60 mph62.4 mph+2.4 mph
65 mph67.6 mph+2.6 mph
70 mph72.8 mph+2.8 mph
75 mph78.0 mph+3.0 mph
80 mph83.2 mph+3.2 mph

Each size on its own

Questions

Which is bigger, 305/35R22 or 305/40R22?
305/40R22 is taller by 1.20 inches (31.61" vs 30.41"). 305/35R22 is the same width.
Can I replace 305/35R22 with 305/40R22?
It is not recommended without checking carefully. The diameter difference is +3.9%, 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 305/35R22), your real speed is 62.4 mph. Your odometer will under-count miles by about 3.9%.
Will 305/40R22 lift my vehicle?
Ride height changes by half the diameter difference: +0.60 inches of ground clearance at the axle.

Other comparisons