Tire Size Box

355/30R20 vs 345/35R20

345/35R20 compared with 355/30R20

+4.0% diameter, −0.4" width

345/35R20 is 29.51" tall vs 28.39". More than the 3% rule of thumb, so check carefully before switching.

28.4"20" rim4.2"14.0" wide
355/30R20 (solid) compared with 345/35R20 (dashed outline), drawn to scale

With 345/35R20 tires, when your speedometer says 60 mph you are really going

62.4 mph

345/35R20 is +1.12 inches (+4.0%) in overall diameter. That is more than the 3% most shops and makers recommend.

355/30R20345/35R20Difference%
Overall diameter28.39"29.51"+1.12"+4.0%
Section width13.98"13.58"−0.39"−2.8%
Sidewall height4.19"4.75"+0.56"+13.4%
Circumference89.18"92.70"+3.53"+4.0%
Revolutions per mile710.5683.5−27.0−3.8%

Speedometer difference

If your vehicle came with 355/30R20 and you fit 345/35R20, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph20.8 mph+0.8 mph
30 mph31.2 mph+1.2 mph
40 mph41.6 mph+1.6 mph
50 mph52.0 mph+2.0 mph
60 mph62.4 mph+2.4 mph
65 mph67.6 mph+2.6 mph
70 mph72.8 mph+2.8 mph
75 mph78.0 mph+3.0 mph
80 mph83.2 mph+3.2 mph

Each size on its own

Questions

Which is bigger, 355/30R20 or 345/35R20?
345/35R20 is taller by 1.12 inches (29.51" vs 28.39"). 355/30R20 is wider by 0.39 inches.
Can I replace 355/30R20 with 345/35R20?
It is not recommended without checking carefully. The diameter difference is +4.0%, 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 345/35R20 change my speedometer?
When your speedometer reads 60 mph with 345/35R20 fitted (calibrated for 355/30R20), your real speed is 62.4 mph. Your odometer will under-count miles by about 4.0%.
Will 345/35R20 lift my vehicle?
Ride height changes by half the diameter difference: +0.56 inches of ground clearance at the axle.

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