Tire Size Box

295/40R18 vs 295/50R18

295/50R18 compared with 295/40R18

+8.5% diameter, 0.0" width

295/50R18 is 29.61" tall vs 27.29". More than the 3% rule of thumb, so check carefully before switching.

27.3"18" rim4.6"11.6" wide
295/40R18 (solid) compared with 295/50R18 (dashed outline), drawn to scale

With 295/50R18 tires, when your speedometer says 60 mph you are really going

65.1 mph

295/50R18 is +2.32 inches (+8.5%) in overall diameter. That is more than the 3% most shops and makers recommend.

295/40R18295/50R18Difference%
Overall diameter27.29"29.61"+2.32"+8.5%
Section width11.61"11.61"0.00"0.0%
Sidewall height4.65"5.81"+1.16"+25.0%
Circumference85.74"93.04"+7.30"+8.5%
Revolutions per mile739.0681.0−58.0−7.8%

Speedometer difference

If your vehicle came with 295/40R18 and you fit 295/50R18, 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 mph43.4 mph+3.4 mph
50 mph54.3 mph+4.3 mph
60 mph65.1 mph+5.1 mph
65 mph70.5 mph+5.5 mph
70 mph76.0 mph+6.0 mph
75 mph81.4 mph+6.4 mph
80 mph86.8 mph+6.8 mph

Each size on its own

Questions

Which is bigger, 295/40R18 or 295/50R18?
295/50R18 is taller by 2.32 inches (29.61" vs 27.29"). 295/40R18 is the same width.
Can I replace 295/40R18 with 295/50R18?
It is not recommended without checking carefully. The diameter difference is +8.5%, 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 295/50R18 change my speedometer?
When your speedometer reads 60 mph with 295/50R18 fitted (calibrated for 295/40R18), your real speed is 65.1 mph. Your odometer will under-count miles by about 8.5%.
Will 295/50R18 lift my vehicle?
Ride height changes by half the diameter difference: +1.16 inches of ground clearance at the axle.

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