Tire Size Box

245/40R17 vs 245/50R17

245/50R17 compared with 245/40R17

+7.8% diameter, 0.0" width

245/50R17 is 26.65" tall vs 24.72". More than the 3% rule of thumb, so check carefully before switching.

24.7"17" rim3.9"9.6" wide
245/40R17 (solid) compared with 245/50R17 (dashed outline), drawn to scale

With 245/50R17 tires, when your speedometer says 60 mph you are really going

64.7 mph

245/50R17 is +1.93 inches (+7.8%) in overall diameter. That is more than the 3% most shops and makers recommend.

245/40R17245/50R17Difference%
Overall diameter24.72"26.65"+1.93"+7.8%
Section width9.65"9.65"0.00"0.0%
Sidewall height3.86"4.82"+0.96"+25.0%
Circumference77.65"83.71"+6.06"+7.8%
Revolutions per mile816.0756.9−59.1−7.2%

Speedometer difference

If your vehicle came with 245/40R17 and you fit 245/50R17, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph21.6 mph+1.6 mph
30 mph32.3 mph+2.3 mph
40 mph43.1 mph+3.1 mph
50 mph53.9 mph+3.9 mph
60 mph64.7 mph+4.7 mph
65 mph70.1 mph+5.1 mph
70 mph75.5 mph+5.5 mph
75 mph80.9 mph+5.9 mph
80 mph86.2 mph+6.2 mph

Each size on its own

Questions

Which is bigger, 245/40R17 or 245/50R17?
245/50R17 is taller by 1.93 inches (26.65" vs 24.72"). 245/40R17 is the same width.
Can I replace 245/40R17 with 245/50R17?
It is not recommended without checking carefully. The diameter difference is +7.8%, 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 245/50R17 change my speedometer?
When your speedometer reads 60 mph with 245/50R17 fitted (calibrated for 245/40R17), your real speed is 64.7 mph. Your odometer will under-count miles by about 7.8%.
Will 245/50R17 lift my vehicle?
Ride height changes by half the diameter difference: +0.96 inches of ground clearance at the axle.

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