Tire Size Box

235/30R22 vs 235/40R22

235/40R22 compared with 235/30R22

+6.7% diameter, 0.0" width

235/40R22 is 29.40" tall vs 27.55". More than the 3% rule of thumb, so check carefully before switching.

27.6"22" rim2.8"9.3" wide
235/30R22 (solid) compared with 235/40R22 (dashed outline), drawn to scale

With 235/40R22 tires, when your speedometer says 60 mph you are really going

64.0 mph

235/40R22 is +1.85 inches (+6.7%) in overall diameter. That is more than the 3% most shops and makers recommend.

235/30R22235/40R22Difference%
Overall diameter27.55"29.40"+1.85"+6.7%
Section width9.25"9.25"0.00"0.0%
Sidewall height2.78"3.70"+0.93"+33.3%
Circumference86.55"92.37"+5.81"+6.7%
Revolutions per mile732.0686.0−46.1−6.3%

Speedometer difference

If your vehicle came with 235/30R22 and you fit 235/40R22, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph21.3 mph+1.3 mph
30 mph32.0 mph+2.0 mph
40 mph42.7 mph+2.7 mph
50 mph53.4 mph+3.4 mph
60 mph64.0 mph+4.0 mph
65 mph69.4 mph+4.4 mph
70 mph74.7 mph+4.7 mph
75 mph80.0 mph+5.0 mph
80 mph85.4 mph+5.4 mph

Each size on its own

Questions

Which is bigger, 235/30R22 or 235/40R22?
235/40R22 is taller by 1.85 inches (29.40" vs 27.55"). 235/30R22 is the same width.
Can I replace 235/30R22 with 235/40R22?
It is not recommended without checking carefully. The diameter difference is +6.7%, 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 235/40R22 change my speedometer?
When your speedometer reads 60 mph with 235/40R22 fitted (calibrated for 235/30R22), your real speed is 64.0 mph. Your odometer will under-count miles by about 6.7%.
Will 235/40R22 lift my vehicle?
Ride height changes by half the diameter difference: +0.93 inches of ground clearance at the axle.

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