Tire Size Box

225/35R21 vs 225/45R21

225/45R21 compared with 225/35R21

+6.5% diameter, 0.0" width

225/45R21 is 28.97" tall vs 27.20". More than the 3% rule of thumb, so check carefully before switching.

27.2"21" rim3.1"8.9" wide
225/35R21 (solid) compared with 225/45R21 (dashed outline), drawn to scale

With 225/45R21 tires, when your speedometer says 60 mph you are really going

63.9 mph

225/45R21 is +1.77 inches (+6.5%) in overall diameter. That is more than the 3% most shops and makers recommend.

225/35R21225/45R21Difference%
Overall diameter27.20"28.97"+1.77"+6.5%
Section width8.86"8.86"0.00"0.0%
Sidewall height3.10"3.99"+0.89"+28.6%
Circumference85.45"91.02"+5.57"+6.5%
Revolutions per mile741.5696.1−45.3−6.1%

Speedometer difference

If your vehicle came with 225/35R21 and you fit 225/45R21, 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 mph42.6 mph+2.6 mph
50 mph53.3 mph+3.3 mph
60 mph63.9 mph+3.9 mph
65 mph69.2 mph+4.2 mph
70 mph74.6 mph+4.6 mph
75 mph79.9 mph+4.9 mph
80 mph85.2 mph+5.2 mph

Each size on its own

Questions

Which is bigger, 225/35R21 or 225/45R21?
225/45R21 is taller by 1.77 inches (28.97" vs 27.20"). 225/35R21 is the same width.
Can I replace 225/35R21 with 225/45R21?
It is not recommended without checking carefully. The diameter difference is +6.5%, 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 225/45R21 change my speedometer?
When your speedometer reads 60 mph with 225/45R21 fitted (calibrated for 225/35R21), your real speed is 63.9 mph. Your odometer will under-count miles by about 6.5%.
Will 225/45R21 lift my vehicle?
Ride height changes by half the diameter difference: +0.89 inches of ground clearance at the axle.

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