Tire Size Box

265/40R20 vs 265/45R20

265/45R20 compared with 265/40R20

+3.7% diameter, 0.0" width

265/45R20 is 29.39" tall vs 28.35". More than the 3% rule of thumb, so check carefully before switching.

28.3"20" rim4.2"10.4" wide
265/40R20 (solid) compared with 265/45R20 (dashed outline), drawn to scale

With 265/45R20 tires, when your speedometer says 60 mph you are really going

62.2 mph

265/45R20 is +1.04 inches (+3.7%) in overall diameter. That is more than the 3% most shops and makers recommend.

265/40R20265/45R20Difference%
Overall diameter28.35"29.39"+1.04"+3.7%
Section width10.43"10.43"0.00"0.0%
Sidewall height4.17"4.69"+0.52"+12.5%
Circumference89.05"92.33"+3.28"+3.7%
Revolutions per mile711.5686.2−25.3−3.5%

Speedometer difference

If your vehicle came with 265/40R20 and you fit 265/45R20, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph20.7 mph+0.7 mph
30 mph31.1 mph+1.1 mph
40 mph41.5 mph+1.5 mph
50 mph51.8 mph+1.8 mph
60 mph62.2 mph+2.2 mph
65 mph67.4 mph+2.4 mph
70 mph72.6 mph+2.6 mph
75 mph77.8 mph+2.8 mph
80 mph82.9 mph+2.9 mph

Each size on its own

Questions

Which is bigger, 265/40R20 or 265/45R20?
265/45R20 is taller by 1.04 inches (29.39" vs 28.35"). 265/40R20 is the same width.
Can I replace 265/40R20 with 265/45R20?
It is not recommended without checking carefully. The diameter difference is +3.7%, 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 265/45R20 change my speedometer?
When your speedometer reads 60 mph with 265/45R20 fitted (calibrated for 265/40R20), your real speed is 62.2 mph. Your odometer will under-count miles by about 3.7%.
Will 265/45R20 lift my vehicle?
Ride height changes by half the diameter difference: +0.52 inches of ground clearance at the axle.

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