Tire Size Box

355/30R24 vs 355/40R24

355/40R24 compared with 355/30R24

+8.6% diameter, 0.0" width

355/40R24 is 35.18" tall vs 32.39". More than the 3% rule of thumb, so check carefully before switching.

32.4"24" rim4.2"14.0" wide
355/30R24 (solid) compared with 355/40R24 (dashed outline), drawn to scale

With 355/40R24 tires, when your speedometer says 60 mph you are really going

65.2 mph

355/40R24 is +2.80 inches (+8.6%) in overall diameter. That is more than the 3% most shops and makers recommend.

355/30R24355/40R24Difference%
Overall diameter32.39"35.18"+2.80"+8.6%
Section width13.98"13.98"0.00"0.0%
Sidewall height4.19"5.59"+1.40"+33.3%
Circumference101.74"110.52"+8.78"+8.6%
Revolutions per mile622.7573.3−49.5−7.9%

Speedometer difference

If your vehicle came with 355/30R24 and you fit 355/40R24, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph21.7 mph+1.7 mph
30 mph32.6 mph+2.6 mph
40 mph43.5 mph+3.5 mph
50 mph54.3 mph+4.3 mph
60 mph65.2 mph+5.2 mph
65 mph70.6 mph+5.6 mph
70 mph76.0 mph+6.0 mph
75 mph81.5 mph+6.5 mph
80 mph86.9 mph+6.9 mph

Each size on its own

Questions

Which is bigger, 355/30R24 or 355/40R24?
355/40R24 is taller by 2.80 inches (35.18" vs 32.39"). 355/30R24 is the same width.
Can I replace 355/30R24 with 355/40R24?
It is not recommended without checking carefully. The diameter difference is +8.6%, 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 355/40R24 change my speedometer?
When your speedometer reads 60 mph with 355/40R24 fitted (calibrated for 355/30R24), your real speed is 65.2 mph. Your odometer will under-count miles by about 8.6%.
Will 355/40R24 lift my vehicle?
Ride height changes by half the diameter difference: +1.40 inches of ground clearance at the axle.

Other comparisons