Tire Size Box

245/35R21 vs 245/45R21

245/45R21 compared with 245/35R21

+7.0% diameter, 0.0" width

245/45R21 is 29.68" tall vs 27.75". More than the 3% rule of thumb, so check carefully before switching.

27.8"21" rim3.4"9.6" wide
245/35R21 (solid) compared with 245/45R21 (dashed outline), drawn to scale

With 245/45R21 tires, when your speedometer says 60 mph you are really going

64.2 mph

245/45R21 is +1.93 inches (+7.0%) in overall diameter. That is more than the 3% most shops and makers recommend.

245/35R21245/45R21Difference%
Overall diameter27.75"29.68"+1.93"+7.0%
Section width9.65"9.65"0.00"0.0%
Sidewall height3.38"4.34"+0.96"+28.6%
Circumference87.19"93.25"+6.06"+7.0%
Revolutions per mile726.7679.5−47.2−6.5%

Speedometer difference

If your vehicle came with 245/35R21 and you fit 245/45R21, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph21.4 mph+1.4 mph
30 mph32.1 mph+2.1 mph
40 mph42.8 mph+2.8 mph
50 mph53.5 mph+3.5 mph
60 mph64.2 mph+4.2 mph
65 mph69.5 mph+4.5 mph
70 mph74.9 mph+4.9 mph
75 mph80.2 mph+5.2 mph
80 mph85.6 mph+5.6 mph

Each size on its own

Questions

Which is bigger, 245/35R21 or 245/45R21?
245/45R21 is taller by 1.93 inches (29.68" vs 27.75"). 245/35R21 is the same width.
Can I replace 245/35R21 with 245/45R21?
It is not recommended without checking carefully. The diameter difference is +7.0%, 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 245/45R21 change my speedometer?
When your speedometer reads 60 mph with 245/45R21 fitted (calibrated for 245/35R21), your real speed is 64.2 mph. Your odometer will under-count miles by about 7.0%.
Will 245/45R21 lift my vehicle?
Ride height changes by half the diameter difference: +0.96 inches of ground clearance at the axle.

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