Tire Size Box

255/40R16 vs 255/45R16

255/45R16 compared with 255/40R16

+4.2% diameter, 0.0" width

255/45R16 is 25.04" tall vs 24.03". More than the 3% rule of thumb, so check carefully before switching.

24.0"16" rim4.0"10.0" wide
255/40R16 (solid) compared with 255/45R16 (dashed outline), drawn to scale

With 255/45R16 tires, when your speedometer says 60 mph you are really going

62.5 mph

255/45R16 is +1.00 inches (+4.2%) in overall diameter. That is more than the 3% most shops and makers recommend.

255/40R16255/45R16Difference%
Overall diameter24.03"25.04"+1.00"+4.2%
Section width10.04"10.04"0.00"0.0%
Sidewall height4.02"4.52"+0.50"+12.5%
Circumference75.50"78.65"+3.15"+4.2%
Revolutions per mile839.2805.6−33.7−4.0%

Speedometer difference

If your vehicle came with 255/40R16 and you fit 255/45R16, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph20.8 mph+0.8 mph
30 mph31.3 mph+1.3 mph
40 mph41.7 mph+1.7 mph
50 mph52.1 mph+2.1 mph
60 mph62.5 mph+2.5 mph
65 mph67.7 mph+2.7 mph
70 mph72.9 mph+2.9 mph
75 mph78.1 mph+3.1 mph
80 mph83.3 mph+3.3 mph

Each size on its own

Questions

Which is bigger, 255/40R16 or 255/45R16?
255/45R16 is taller by 1.00 inches (25.04" vs 24.03"). 255/40R16 is the same width.
Can I replace 255/40R16 with 255/45R16?
It is not recommended without checking carefully. The diameter difference is +4.2%, 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 255/45R16 change my speedometer?
When your speedometer reads 60 mph with 255/45R16 fitted (calibrated for 255/40R16), your real speed is 62.5 mph. Your odometer will under-count miles by about 4.2%.
Will 255/45R16 lift my vehicle?
Ride height changes by half the diameter difference: +0.50 inches of ground clearance at the axle.

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