Tire Size Box

235/35R21 vs 235/45R21

235/45R21 compared with 235/35R21

+6.7% diameter, 0.0" width

235/45R21 is 29.33" tall vs 27.48". More than the 3% rule of thumb, so check carefully before switching.

27.5"21" rim3.2"9.3" wide
235/35R21 (solid) compared with 235/45R21 (dashed outline), drawn to scale

With 235/45R21 tires, when your speedometer says 60 mph you are really going

64.0 mph

235/45R21 is +1.85 inches (+6.7%) in overall diameter. That is more than the 3% most shops and makers recommend.

235/35R21235/45R21Difference%
Overall diameter27.48"29.33"+1.85"+6.7%
Section width9.25"9.25"0.00"0.0%
Sidewall height3.24"4.16"+0.93"+28.6%
Circumference86.32"92.13"+5.81"+6.7%
Revolutions per mile734.0687.7−46.3−6.3%

Speedometer difference

If your vehicle came with 235/35R21 and you fit 235/45R21, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph21.3 mph+1.3 mph
30 mph32.0 mph+2.0 mph
40 mph42.7 mph+2.7 mph
50 mph53.4 mph+3.4 mph
60 mph64.0 mph+4.0 mph
65 mph69.4 mph+4.4 mph
70 mph74.7 mph+4.7 mph
75 mph80.1 mph+5.1 mph
80 mph85.4 mph+5.4 mph

Each size on its own

Questions

Which is bigger, 235/35R21 or 235/45R21?
235/45R21 is taller by 1.85 inches (29.33" vs 27.48"). 235/35R21 is the same width.
Can I replace 235/35R21 with 235/45R21?
It is not recommended without checking carefully. The diameter difference is +6.7%, 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 235/45R21 change my speedometer?
When your speedometer reads 60 mph with 235/45R21 fitted (calibrated for 235/35R21), your real speed is 64.0 mph. Your odometer will under-count miles by about 6.7%.
Will 235/45R21 lift my vehicle?
Ride height changes by half the diameter difference: +0.93 inches of ground clearance at the axle.

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