Tire Size Box

295/35R21 vs 295/40R21

295/40R21 compared with 295/35R21

+4.0% diameter, 0.0" width

295/40R21 is 30.29" tall vs 29.13". More than the 3% rule of thumb, so check carefully before switching.

29.1"21" rim4.1"11.6" wide
295/35R21 (solid) compared with 295/40R21 (dashed outline), drawn to scale

With 295/40R21 tires, when your speedometer says 60 mph you are really going

62.4 mph

295/40R21 is +1.16 inches (+4.0%) in overall diameter. That is more than the 3% most shops and makers recommend.

295/35R21295/40R21Difference%
Overall diameter29.13"30.29"+1.16"+4.0%
Section width11.61"11.61"0.00"0.0%
Sidewall height4.06"4.65"+0.58"+14.3%
Circumference91.51"95.16"+3.65"+4.0%
Revolutions per mile692.4665.8−26.5−3.8%

Speedometer difference

If your vehicle came with 295/35R21 and you fit 295/40R21, 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, 295/35R21 or 295/40R21?
295/40R21 is taller by 1.16 inches (30.29" vs 29.13"). 295/35R21 is the same width.
Can I replace 295/35R21 with 295/40R21?
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 295/40R21 change my speedometer?
When your speedometer reads 60 mph with 295/40R21 fitted (calibrated for 295/35R21), your real speed is 62.4 mph. Your odometer will under-count miles by about 4.0%.
Will 295/40R21 lift my vehicle?
Ride height changes by half the diameter difference: +0.58 inches of ground clearance at the axle.

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