Tire Size Box

345/25R21 vs 345/35R21

345/35R21 compared with 345/25R21

+9.8% diameter, 0.0" width

345/35R21 is 30.51" tall vs 27.79". More than the 3% rule of thumb, so check carefully before switching.

27.8"21" rim3.4"13.6" wide
345/25R21 (solid) compared with 345/35R21 (dashed outline), drawn to scale

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

65.9 mph

345/35R21 is +2.72 inches (+9.8%) in overall diameter. That is more than the 3% most shops and makers recommend.

345/25R21345/35R21Difference%
Overall diameter27.79"30.51"+2.72"+9.8%
Section width13.58"13.58"0.00"0.0%
Sidewall height3.40"4.75"+1.36"+40.0%
Circumference87.31"95.84"+8.53"+9.8%
Revolutions per mile725.7661.1−64.6−8.9%

Speedometer difference

If your vehicle came with 345/25R21 and you fit 345/35R21, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph22.0 mph+2.0 mph
30 mph32.9 mph+2.9 mph
40 mph43.9 mph+3.9 mph
50 mph54.9 mph+4.9 mph
60 mph65.9 mph+5.9 mph
65 mph71.4 mph+6.4 mph
70 mph76.8 mph+6.8 mph
75 mph82.3 mph+7.3 mph
80 mph87.8 mph+7.8 mph

Each size on its own

Questions

Which is bigger, 345/25R21 or 345/35R21?
345/35R21 is taller by 2.72 inches (30.51" vs 27.79"). 345/25R21 is the same width.
Can I replace 345/25R21 with 345/35R21?
It is not recommended without checking carefully. The diameter difference is +9.8%, 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 345/35R21 change my speedometer?
When your speedometer reads 60 mph with 345/35R21 fitted (calibrated for 345/25R21), your real speed is 65.9 mph. Your odometer will under-count miles by about 9.8%.
Will 345/35R21 lift my vehicle?
Ride height changes by half the diameter difference: +1.36 inches of ground clearance at the axle.

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