Tire Size Box

275/40R17 vs 275/45R17

275/45R17 compared with 275/40R17

+4.2% diameter, 0.0" width

275/45R17 is 26.74" tall vs 25.66". More than the 3% rule of thumb, so check carefully before switching.

25.7"17" rim4.3"10.8" wide
275/40R17 (solid) compared with 275/45R17 (dashed outline), drawn to scale

With 275/45R17 tires, when your speedometer says 60 mph you are really going

62.5 mph

275/45R17 is +1.08 inches (+4.2%) in overall diameter. That is more than the 3% most shops and makers recommend.

275/40R17275/45R17Difference%
Overall diameter25.66"26.74"+1.08"+4.2%
Section width10.83"10.83"0.00"0.0%
Sidewall height4.33"4.87"+0.54"+12.5%
Circumference80.62"84.02"+3.40"+4.2%
Revolutions per mile785.9754.1−31.8−4.0%

Speedometer difference

If your vehicle came with 275/40R17 and you fit 275/45R17, 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 mph73.0 mph+3.0 mph
75 mph78.2 mph+3.2 mph
80 mph83.4 mph+3.4 mph

Each size on its own

Questions

Which is bigger, 275/40R17 or 275/45R17?
275/45R17 is taller by 1.08 inches (26.74" vs 25.66"). 275/40R17 is the same width.
Can I replace 275/40R17 with 275/45R17?
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 275/45R17 change my speedometer?
When your speedometer reads 60 mph with 275/45R17 fitted (calibrated for 275/40R17), your real speed is 62.5 mph. Your odometer will under-count miles by about 4.2%.
Will 275/45R17 lift my vehicle?
Ride height changes by half the diameter difference: +0.54 inches of ground clearance at the axle.

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