Tire Size Box

355/30R21 vs 355/35R21

355/35R21 compared with 355/30R21

+4.8% diameter, 0.0" width

355/35R21 is 30.78" tall vs 29.39". More than the 3% rule of thumb, so check carefully before switching.

29.4"21" rim4.2"14.0" wide
355/30R21 (solid) compared with 355/35R21 (dashed outline), drawn to scale

With 355/35R21 tires, when your speedometer says 60 mph you are really going

62.9 mph

355/35R21 is +1.40 inches (+4.8%) in overall diameter. That is more than the 3% most shops and makers recommend.

355/30R21355/35R21Difference%
Overall diameter29.39"30.78"+1.40"+4.8%
Section width13.98"13.98"0.00"0.0%
Sidewall height4.19"4.89"+0.70"+16.7%
Circumference92.32"96.71"+4.39"+4.8%
Revolutions per mile686.3655.2−31.2−4.5%

Speedometer difference

If your vehicle came with 355/30R21 and you fit 355/35R21, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph21.0 mph+1.0 mph
30 mph31.4 mph+1.4 mph
40 mph41.9 mph+1.9 mph
50 mph52.4 mph+2.4 mph
60 mph62.9 mph+2.9 mph
65 mph68.1 mph+3.1 mph
70 mph73.3 mph+3.3 mph
75 mph78.6 mph+3.6 mph
80 mph83.8 mph+3.8 mph

Each size on its own

Questions

Which is bigger, 355/30R21 or 355/35R21?
355/35R21 is taller by 1.40 inches (30.78" vs 29.39"). 355/30R21 is the same width.
Can I replace 355/30R21 with 355/35R21?
It is not recommended without checking carefully. The diameter difference is +4.8%, 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 355/35R21 change my speedometer?
When your speedometer reads 60 mph with 355/35R21 fitted (calibrated for 355/30R21), your real speed is 62.9 mph. Your odometer will under-count miles by about 4.8%.
Will 355/35R21 lift my vehicle?
Ride height changes by half the diameter difference: +0.70 inches of ground clearance at the axle.

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