Tire Size Box

275/35R21 vs 275/45R21

275/45R21 compared with 275/35R21

+7.6% diameter, 0.0" width

275/45R21 is 30.74" tall vs 28.58". More than the 3% rule of thumb, so check carefully before switching.

28.6"21" rim3.8"10.8" wide
275/35R21 (solid) compared with 275/45R21 (dashed outline), drawn to scale

With 275/45R21 tires, when your speedometer says 60 mph you are really going

64.5 mph

275/45R21 is +2.17 inches (+7.6%) in overall diameter. That is more than the 3% most shops and makers recommend.

275/35R21275/45R21Difference%
Overall diameter28.58"30.74"+2.17"+7.6%
Section width10.83"10.83"0.00"0.0%
Sidewall height3.79"4.87"+1.08"+28.6%
Circumference89.78"96.59"+6.80"+7.6%
Revolutions per mile705.7656.0−49.7−7.0%

Speedometer difference

If your vehicle came with 275/35R21 and you fit 275/45R21, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph21.5 mph+1.5 mph
30 mph32.3 mph+2.3 mph
40 mph43.0 mph+3.0 mph
50 mph53.8 mph+3.8 mph
60 mph64.5 mph+4.5 mph
65 mph69.9 mph+4.9 mph
70 mph75.3 mph+5.3 mph
75 mph80.7 mph+5.7 mph
80 mph86.1 mph+6.1 mph

Each size on its own

Questions

Which is bigger, 275/35R21 or 275/45R21?
275/45R21 is taller by 2.17 inches (30.74" vs 28.58"). 275/35R21 is the same width.
Can I replace 275/35R21 with 275/45R21?
It is not recommended without checking carefully. The diameter difference is +7.6%, 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 275/45R21 change my speedometer?
When your speedometer reads 60 mph with 275/45R21 fitted (calibrated for 275/35R21), your real speed is 64.5 mph. Your odometer will under-count miles by about 7.6%.
Will 275/45R21 lift my vehicle?
Ride height changes by half the diameter difference: +1.08 inches of ground clearance at the axle.

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