Tire Size Box

215/40R20 vs 215/45R20

215/45R20 compared with 215/40R20

+3.2% diameter, 0.0" width

215/45R20 is 27.62" tall vs 26.77". More than the 3% rule of thumb, so check carefully before switching.

26.8"20" rim3.4"8.5" wide
215/40R20 (solid) compared with 215/45R20 (dashed outline), drawn to scale

With 215/45R20 tires, when your speedometer says 60 mph you are really going

61.9 mph

215/45R20 is +0.85 inches (+3.2%) in overall diameter. That is more than the 3% most shops and makers recommend.

215/40R20215/45R20Difference%
Overall diameter26.77"27.62"+0.85"+3.2%
Section width8.46"8.46"0.00"0.0%
Sidewall height3.39"3.81"+0.42"+12.5%
Circumference84.11"86.76"+2.66"+3.2%
Revolutions per mile753.3730.2−23.1−3.1%

Speedometer difference

If your vehicle came with 215/40R20 and you fit 215/45R20, 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 mph41.3 mph+1.3 mph
50 mph51.6 mph+1.6 mph
60 mph61.9 mph+1.9 mph
65 mph67.1 mph+2.1 mph
70 mph72.2 mph+2.2 mph
75 mph77.4 mph+2.4 mph
80 mph82.5 mph+2.5 mph

Each size on its own

Questions

Which is bigger, 215/40R20 or 215/45R20?
215/45R20 is taller by 0.85 inches (27.62" vs 26.77"). 215/40R20 is the same width.
Can I replace 215/40R20 with 215/45R20?
It is not recommended without checking carefully. The diameter difference is +3.2%, 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 215/45R20 change my speedometer?
When your speedometer reads 60 mph with 215/45R20 fitted (calibrated for 215/40R20), your real speed is 61.9 mph. Your odometer will under-count miles by about 3.2%.
Will 215/45R20 lift my vehicle?
Ride height changes by half the diameter difference: +0.42 inches of ground clearance at the axle.

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