Tire Size Box

235/30R21 vs 235/35R21

235/35R21 compared with 235/30R21

+3.5% diameter, 0.0" width

235/35R21 is 27.48" tall vs 26.55". More than the 3% rule of thumb, so check carefully before switching.

26.6"21" rim2.8"9.3" wide
235/30R21 (solid) compared with 235/35R21 (dashed outline), drawn to scale

With 235/35R21 tires, when your speedometer says 60 mph you are really going

62.1 mph

235/35R21 is +0.93 inches (+3.5%) in overall diameter. That is more than the 3% most shops and makers recommend.

235/30R21235/35R21Difference%
Overall diameter26.55"27.48"+0.93"+3.5%
Section width9.25"9.25"0.00"0.0%
Sidewall height2.78"3.24"+0.46"+16.7%
Circumference83.41"86.32"+2.91"+3.5%
Revolutions per mile759.6734.0−25.6−3.4%

Speedometer difference

If your vehicle came with 235/30R21 and you fit 235/35R21, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph20.7 mph+0.7 mph
30 mph31.0 mph+1.0 mph
40 mph41.4 mph+1.4 mph
50 mph51.7 mph+1.7 mph
60 mph62.1 mph+2.1 mph
65 mph67.3 mph+2.3 mph
70 mph72.4 mph+2.4 mph
75 mph77.6 mph+2.6 mph
80 mph82.8 mph+2.8 mph

Each size on its own

Questions

Which is bigger, 235/30R21 or 235/35R21?
235/35R21 is taller by 0.93 inches (27.48" vs 26.55"). 235/30R21 is the same width.
Can I replace 235/30R21 with 235/35R21?
It is not recommended without checking carefully. The diameter difference is +3.5%, 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 235/35R21 change my speedometer?
When your speedometer reads 60 mph with 235/35R21 fitted (calibrated for 235/30R21), your real speed is 62.1 mph. Your odometer will under-count miles by about 3.5%.
Will 235/35R21 lift my vehicle?
Ride height changes by half the diameter difference: +0.46 inches of ground clearance at the axle.

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