Tire Size Box

355/35R20 vs 355/45R20

355/45R20 compared with 355/35R20

+9.4% diameter, 0.0" width

355/45R20 is 32.58" tall vs 29.78". More than the 3% rule of thumb, so check carefully before switching.

29.8"20" rim4.9"14.0" wide
355/35R20 (solid) compared with 355/45R20 (dashed outline), drawn to scale

With 355/45R20 tires, when your speedometer says 60 mph you are really going

65.6 mph

355/45R20 is +2.80 inches (+9.4%) in overall diameter. That is more than the 3% most shops and makers recommend.

355/35R20355/45R20Difference%
Overall diameter29.78"32.58"+2.80"+9.4%
Section width13.98"13.98"0.00"0.0%
Sidewall height4.89"6.29"+1.40"+28.6%
Circumference93.57"102.35"+8.78"+9.4%
Revolutions per mile677.2619.1−58.1−8.6%

Speedometer difference

If your vehicle came with 355/35R20 and you fit 355/45R20, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph21.9 mph+1.9 mph
30 mph32.8 mph+2.8 mph
40 mph43.8 mph+3.8 mph
50 mph54.7 mph+4.7 mph
60 mph65.6 mph+5.6 mph
65 mph71.1 mph+6.1 mph
70 mph76.6 mph+6.6 mph
75 mph82.0 mph+7.0 mph
80 mph87.5 mph+7.5 mph

Each size on its own

Questions

Which is bigger, 355/35R20 or 355/45R20?
355/45R20 is taller by 2.80 inches (32.58" vs 29.78"). 355/35R20 is the same width.
Can I replace 355/35R20 with 355/45R20?
It is not recommended without checking carefully. The diameter difference is +9.4%, 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 355/45R20 change my speedometer?
When your speedometer reads 60 mph with 355/45R20 fitted (calibrated for 355/35R20), your real speed is 65.6 mph. Your odometer will under-count miles by about 9.4%.
Will 355/45R20 lift my vehicle?
Ride height changes by half the diameter difference: +1.40 inches of ground clearance at the axle.

Other comparisons