Tire Size Box

345/30R21 vs 345/35R21

345/35R21 compared with 345/30R21

+4.7% diameter, 0.0" width

345/35R21 is 30.51" tall vs 29.15". More than the 3% rule of thumb, so check carefully before switching.

29.1"21" rim4.1"13.6" wide
345/30R21 (solid) compared with 345/35R21 (dashed outline), drawn to scale

With 345/35R21 tires, when your speedometer says 60 mph you are really going

62.8 mph

345/35R21 is +1.36 inches (+4.7%) in overall diameter. That is more than the 3% most shops and makers recommend.

345/30R21345/35R21Difference%
Overall diameter29.15"30.51"+1.36"+4.7%
Section width13.58"13.58"0.00"0.0%
Sidewall height4.07"4.75"+0.68"+16.7%
Circumference91.58"95.84"+4.27"+4.7%
Revolutions per mile691.9661.1−30.8−4.5%

Speedometer difference

If your vehicle came with 345/30R21 and you fit 345/35R21, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph20.9 mph+0.9 mph
30 mph31.4 mph+1.4 mph
40 mph41.9 mph+1.9 mph
50 mph52.3 mph+2.3 mph
60 mph62.8 mph+2.8 mph
65 mph68.0 mph+3.0 mph
70 mph73.3 mph+3.3 mph
75 mph78.5 mph+3.5 mph
80 mph83.7 mph+3.7 mph

Each size on its own

Questions

Which is bigger, 345/30R21 or 345/35R21?
345/35R21 is taller by 1.36 inches (30.51" vs 29.15"). 345/30R21 is the same width.
Can I replace 345/30R21 with 345/35R21?
It is not recommended without checking carefully. The diameter difference is +4.7%, 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 345/35R21 change my speedometer?
When your speedometer reads 60 mph with 345/35R21 fitted (calibrated for 345/30R21), your real speed is 62.8 mph. Your odometer will under-count miles by about 4.7%.
Will 345/35R21 lift my vehicle?
Ride height changes by half the diameter difference: +0.68 inches of ground clearance at the axle.

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