Tire Size Box

305/35R20 vs 295/40R20

295/40R20 compared with 305/35R20

+3.1% diameter, −0.4" width

295/40R20 is 29.29" tall vs 28.41". More than the 3% rule of thumb, so check carefully before switching.

28.4"20" rim4.2"12.0" wide
305/35R20 (solid) compared with 295/40R20 (dashed outline), drawn to scale

With 295/40R20 tires, when your speedometer says 60 mph you are really going

61.9 mph

295/40R20 is +0.89 inches (+3.1%) in overall diameter. That is more than the 3% most shops and makers recommend.

305/35R20295/40R20Difference%
Overall diameter28.41"29.29"+0.89"+3.1%
Section width12.01"11.61"−0.39"−3.3%
Sidewall height4.20"4.65"+0.44"+10.5%
Circumference89.24"92.02"+2.78"+3.1%
Revolutions per mile710.0688.5−21.5−3.0%

Speedometer difference

If your vehicle came with 305/35R20 and you fit 295/40R20, 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 mph51.6 mph+1.6 mph
60 mph61.9 mph+1.9 mph
65 mph67.0 mph+2.0 mph
70 mph72.2 mph+2.2 mph
75 mph77.3 mph+2.3 mph
80 mph82.5 mph+2.5 mph

Each size on its own

Questions

Which is bigger, 305/35R20 or 295/40R20?
295/40R20 is taller by 0.89 inches (29.29" vs 28.41"). 305/35R20 is wider by 0.39 inches.
Can I replace 305/35R20 with 295/40R20?
It is not recommended without checking carefully. The diameter difference is +3.1%, 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 295/40R20 change my speedometer?
When your speedometer reads 60 mph with 295/40R20 fitted (calibrated for 305/35R20), your real speed is 61.9 mph. Your odometer will under-count miles by about 3.1%.
Will 295/40R20 lift my vehicle?
Ride height changes by half the diameter difference: +0.44 inches of ground clearance at the axle.

Other comparisons