Tire Size Box

335/40R20 vs 335/45R20

335/45R20 compared with 335/40R20

+4.3% diameter, 0.0" width

335/45R20 is 31.87" tall vs 30.55". More than the 3% rule of thumb, so check carefully before switching.

30.6"20" rim5.3"13.2" wide
335/40R20 (solid) compared with 335/45R20 (dashed outline), drawn to scale

With 335/45R20 tires, when your speedometer says 60 mph you are really going

62.6 mph

335/45R20 is +1.32 inches (+4.3%) in overall diameter. That is more than the 3% most shops and makers recommend.

335/40R20335/45R20Difference%
Overall diameter30.55"31.87"+1.32"+4.3%
Section width13.19"13.19"0.00"0.0%
Sidewall height5.28"5.94"+0.66"+12.5%
Circumference95.98"100.12"+4.14"+4.3%
Revolutions per mile660.1632.8−27.3−4.1%

Speedometer difference

If your vehicle came with 335/40R20 and you fit 335/45R20, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph20.9 mph+0.9 mph
30 mph31.3 mph+1.3 mph
40 mph41.7 mph+1.7 mph
50 mph52.2 mph+2.2 mph
60 mph62.6 mph+2.6 mph
65 mph67.8 mph+2.8 mph
70 mph73.0 mph+3.0 mph
75 mph78.2 mph+3.2 mph
80 mph83.5 mph+3.5 mph

Each size on its own

Questions

Which is bigger, 335/40R20 or 335/45R20?
335/45R20 is taller by 1.32 inches (31.87" vs 30.55"). 335/40R20 is the same width.
Can I replace 335/40R20 with 335/45R20?
It is not recommended without checking carefully. The diameter difference is +4.3%, 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 335/45R20 change my speedometer?
When your speedometer reads 60 mph with 335/45R20 fitted (calibrated for 335/40R20), your real speed is 62.6 mph. Your odometer will under-count miles by about 4.3%.
Will 335/45R20 lift my vehicle?
Ride height changes by half the diameter difference: +0.66 inches of ground clearance at the axle.

Other comparisons