Tire Size Box

345/35R20 vs 345/45R20

345/45R20 compared with 345/35R20

+9.2% diameter, 0.0" width

345/45R20 is 32.22" tall vs 29.51". More than the 3% rule of thumb, so check carefully before switching.

29.5"20" rim4.8"13.6" wide
345/35R20 (solid) compared with 345/45R20 (dashed outline), drawn to scale

With 345/45R20 tires, when your speedometer says 60 mph you are really going

65.5 mph

345/45R20 is +2.72 inches (+9.2%) in overall diameter. That is more than the 3% most shops and makers recommend.

345/35R20345/45R20Difference%
Overall diameter29.51"32.22"+2.72"+9.2%
Section width13.58"13.58"0.00"0.0%
Sidewall height4.75"6.11"+1.36"+28.6%
Circumference92.70"101.24"+8.53"+9.2%
Revolutions per mile683.5625.9−57.6−8.4%

Speedometer difference

If your vehicle came with 345/35R20 and you fit 345/45R20, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph21.8 mph+1.8 mph
30 mph32.8 mph+2.8 mph
40 mph43.7 mph+3.7 mph
50 mph54.6 mph+4.6 mph
60 mph65.5 mph+5.5 mph
65 mph71.0 mph+6.0 mph
70 mph76.4 mph+6.4 mph
75 mph81.9 mph+6.9 mph
80 mph87.4 mph+7.4 mph

Each size on its own

Questions

Which is bigger, 345/35R20 or 345/45R20?
345/45R20 is taller by 2.72 inches (32.22" vs 29.51"). 345/35R20 is the same width.
Can I replace 345/35R20 with 345/45R20?
It is not recommended without checking carefully. The diameter difference is +9.2%, 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 345/45R20 change my speedometer?
When your speedometer reads 60 mph with 345/45R20 fitted (calibrated for 345/35R20), your real speed is 65.5 mph. Your odometer will under-count miles by about 9.2%.
Will 345/45R20 lift my vehicle?
Ride height changes by half the diameter difference: +1.36 inches of ground clearance at the axle.

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