Tire Size Box

255/45R17 vs 255/50R17

255/50R17 compared with 255/45R17

+3.9% diameter, 0.0" width

255/50R17 is 27.04" tall vs 26.04". More than the 3% rule of thumb, so check carefully before switching.

26.0"17" rim4.5"10.0" wide
255/45R17 (solid) compared with 255/50R17 (dashed outline), drawn to scale

With 255/50R17 tires, when your speedometer says 60 mph you are really going

62.3 mph

255/50R17 is +1.00 inches (+3.9%) in overall diameter. That is more than the 3% most shops and makers recommend.

255/45R17255/50R17Difference%
Overall diameter26.04"27.04"+1.00"+3.9%
Section width10.04"10.04"0.00"0.0%
Sidewall height4.52"5.02"+0.50"+11.1%
Circumference81.79"84.95"+3.15"+3.9%
Revolutions per mile774.6745.9−28.8−3.7%

Speedometer difference

If your vehicle came with 255/45R17 and you fit 255/50R17, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph20.8 mph+0.8 mph
30 mph31.2 mph+1.2 mph
40 mph41.5 mph+1.5 mph
50 mph51.9 mph+1.9 mph
60 mph62.3 mph+2.3 mph
65 mph67.5 mph+2.5 mph
70 mph72.7 mph+2.7 mph
75 mph77.9 mph+2.9 mph
80 mph83.1 mph+3.1 mph

Each size on its own

Questions

Which is bigger, 255/45R17 or 255/50R17?
255/50R17 is taller by 1.00 inches (27.04" vs 26.04"). 255/45R17 is the same width.
Can I replace 255/45R17 with 255/50R17?
It is not recommended without checking carefully. The diameter difference is +3.9%, 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 255/50R17 change my speedometer?
When your speedometer reads 60 mph with 255/50R17 fitted (calibrated for 255/45R17), your real speed is 62.3 mph. Your odometer will under-count miles by about 3.9%.
Will 255/50R17 lift my vehicle?
Ride height changes by half the diameter difference: +0.50 inches of ground clearance at the axle.

Other comparisons