Tire Size Box

295/40R21 vs 295/45R21

295/45R21 compared with 295/40R21

+3.8% diameter, 0.0" width

295/45R21 is 31.45" tall vs 30.29". More than the 3% rule of thumb, so check carefully before switching.

30.3"21" rim4.6"11.6" wide
295/40R21 (solid) compared with 295/45R21 (dashed outline), drawn to scale

With 295/45R21 tires, when your speedometer says 60 mph you are really going

62.3 mph

295/45R21 is +1.16 inches (+3.8%) in overall diameter. That is more than the 3% most shops and makers recommend.

295/40R21295/45R21Difference%
Overall diameter30.29"31.45"+1.16"+3.8%
Section width11.61"11.61"0.00"0.0%
Sidewall height4.65"5.23"+0.58"+12.5%
Circumference95.16"98.81"+3.65"+3.8%
Revolutions per mile665.8641.2−24.6−3.7%

Speedometer difference

If your vehicle came with 295/40R21 and you fit 295/45R21, 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 mph41.5 mph+1.5 mph
50 mph51.9 mph+1.9 mph
60 mph62.3 mph+2.3 mph
65 mph67.5 mph+2.5 mph
70 mph72.7 mph+2.7 mph
75 mph77.9 mph+2.9 mph
80 mph83.1 mph+3.1 mph

Each size on its own

Questions

Which is bigger, 295/40R21 or 295/45R21?
295/45R21 is taller by 1.16 inches (31.45" vs 30.29"). 295/40R21 is the same width.
Can I replace 295/40R21 with 295/45R21?
It is not recommended without checking carefully. The diameter difference is +3.8%, 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 295/45R21 change my speedometer?
When your speedometer reads 60 mph with 295/45R21 fitted (calibrated for 295/40R21), your real speed is 62.3 mph. Your odometer will under-count miles by about 3.8%.
Will 295/45R21 lift my vehicle?
Ride height changes by half the diameter difference: +0.58 inches of ground clearance at the axle.

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