Tire Size Box

355/35R21 vs 355/45R21

355/45R21 compared with 355/35R21

+9.1% diameter, 0.0" width

355/45R21 is 33.58" tall vs 30.78". More than the 3% rule of thumb, so check carefully before switching.

30.8"21" rim4.9"14.0" wide
355/35R21 (solid) compared with 355/45R21 (dashed outline), drawn to scale

With 355/45R21 tires, when your speedometer says 60 mph you are really going

65.4 mph

355/45R21 is +2.80 inches (+9.1%) in overall diameter. That is more than the 3% most shops and makers recommend.

355/35R21355/45R21Difference%
Overall diameter30.78"33.58"+2.80"+9.1%
Section width13.98"13.98"0.00"0.0%
Sidewall height4.89"6.29"+1.40"+28.6%
Circumference96.71"105.49"+8.78"+9.1%
Revolutions per mile655.2600.6−54.5−8.3%

Speedometer difference

If your vehicle came with 355/35R21 and you fit 355/45R21, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph21.8 mph+1.8 mph
30 mph32.7 mph+2.7 mph
40 mph43.6 mph+3.6 mph
50 mph54.5 mph+4.5 mph
60 mph65.4 mph+5.4 mph
65 mph70.9 mph+5.9 mph
70 mph76.4 mph+6.4 mph
75 mph81.8 mph+6.8 mph
80 mph87.3 mph+7.3 mph

Each size on its own

Questions

Which is bigger, 355/35R21 or 355/45R21?
355/45R21 is taller by 2.80 inches (33.58" vs 30.78"). 355/35R21 is the same width.
Can I replace 355/35R21 with 355/45R21?
It is not recommended without checking carefully. The diameter difference is +9.1%, 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 355/45R21 change my speedometer?
When your speedometer reads 60 mph with 355/45R21 fitted (calibrated for 355/35R21), your real speed is 65.4 mph. Your odometer will under-count miles by about 9.1%.
Will 355/45R21 lift my vehicle?
Ride height changes by half the diameter difference: +1.40 inches of ground clearance at the axle.

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