Tire Size Box

215/40R18 vs 215/50R18

215/50R18 compared with 215/40R18

+6.8% diameter, 0.0" width

215/50R18 is 26.46" tall vs 24.77". More than the 3% rule of thumb, so check carefully before switching.

24.8"18" rim3.4"8.5" wide
215/40R18 (solid) compared with 215/50R18 (dashed outline), drawn to scale

With 215/50R18 tires, when your speedometer says 60 mph you are really going

64.1 mph

215/50R18 is +1.69 inches (+6.8%) in overall diameter. That is more than the 3% most shops and makers recommend.

215/40R18215/50R18Difference%
Overall diameter24.77"26.46"+1.69"+6.8%
Section width8.46"8.46"0.00"0.0%
Sidewall height3.39"4.23"+0.85"+25.0%
Circumference77.82"83.14"+5.32"+6.8%
Revolutions per mile814.2762.1−52.1−6.4%

Speedometer difference

If your vehicle came with 215/40R18 and you fit 215/50R18, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph21.4 mph+1.4 mph
30 mph32.1 mph+2.1 mph
40 mph42.7 mph+2.7 mph
50 mph53.4 mph+3.4 mph
60 mph64.1 mph+4.1 mph
65 mph69.4 mph+4.4 mph
70 mph74.8 mph+4.8 mph
75 mph80.1 mph+5.1 mph
80 mph85.5 mph+5.5 mph

Each size on its own

Questions

Which is bigger, 215/40R18 or 215/50R18?
215/50R18 is taller by 1.69 inches (26.46" vs 24.77"). 215/40R18 is the same width.
Can I replace 215/40R18 with 215/50R18?
It is not recommended without checking carefully. The diameter difference is +6.8%, 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 215/50R18 change my speedometer?
When your speedometer reads 60 mph with 215/50R18 fitted (calibrated for 215/40R18), your real speed is 64.1 mph. Your odometer will under-count miles by about 6.8%.
Will 215/50R18 lift my vehicle?
Ride height changes by half the diameter difference: +0.85 inches of ground clearance at the axle.

Other comparisons