Tire Size Box

275/35R20 vs 275/45R20

275/45R20 compared with 275/35R20

+7.9% diameter, 0.0" width

275/45R20 is 29.74" tall vs 27.58". More than the 3% rule of thumb, so check carefully before switching.

27.6"20" rim3.8"10.8" wide
275/35R20 (solid) compared with 275/45R20 (dashed outline), drawn to scale

With 275/45R20 tires, when your speedometer says 60 mph you are really going

64.7 mph

275/45R20 is +2.17 inches (+7.9%) in overall diameter. That is more than the 3% most shops and makers recommend.

275/35R20275/45R20Difference%
Overall diameter27.58"29.74"+2.17"+7.9%
Section width10.83"10.83"0.00"0.0%
Sidewall height3.79"4.87"+1.08"+28.6%
Circumference86.64"93.44"+6.80"+7.9%
Revolutions per mile731.3678.1−53.2−7.3%

Speedometer difference

If your vehicle came with 275/35R20 and you fit 275/45R20, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph21.6 mph+1.6 mph
30 mph32.4 mph+2.4 mph
40 mph43.1 mph+3.1 mph
50 mph53.9 mph+3.9 mph
60 mph64.7 mph+4.7 mph
65 mph70.1 mph+5.1 mph
70 mph75.5 mph+5.5 mph
75 mph80.9 mph+5.9 mph
80 mph86.3 mph+6.3 mph

Each size on its own

Questions

Which is bigger, 275/35R20 or 275/45R20?
275/45R20 is taller by 2.17 inches (29.74" vs 27.58"). 275/35R20 is the same width.
Can I replace 275/35R20 with 275/45R20?
It is not recommended without checking carefully. The diameter difference is +7.9%, 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 275/45R20 change my speedometer?
When your speedometer reads 60 mph with 275/45R20 fitted (calibrated for 275/35R20), your real speed is 64.7 mph. Your odometer will under-count miles by about 7.9%.
Will 275/45R20 lift my vehicle?
Ride height changes by half the diameter difference: +1.08 inches of ground clearance at the axle.

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