Tire Size Box

275/65R18 vs 275/75R18

275/75R18 compared with 275/65R18

+6.8% diameter, 0.0" width

275/75R18 is 34.24" tall vs 32.07". More than the 3% rule of thumb, so check carefully before switching.

32.1"18" rim7.0"10.8" wide
275/65R18 (solid) compared with 275/75R18 (dashed outline), drawn to scale

With 275/75R18 tires, when your speedometer says 60 mph you are really going

64.1 mph

275/75R18 is +2.17 inches (+6.8%) in overall diameter. That is more than the 3% most shops and makers recommend.

275/65R18275/75R18Difference%
Overall diameter32.07"34.24"+2.17"+6.8%
Section width10.83"10.83"0.00"0.0%
Sidewall height7.04"8.12"+1.08"+15.4%
Circumference100.77"107.57"+6.80"+6.8%
Revolutions per mile628.8589.0−39.8−6.3%

Speedometer difference

If your vehicle came with 275/65R18 and you fit 275/75R18, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph21.4 mph+1.4 mph
30 mph32.0 mph+2.0 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 mph74.7 mph+4.7 mph
75 mph80.1 mph+5.1 mph
80 mph85.4 mph+5.4 mph

Each size on its own

Questions

Which is bigger, 275/65R18 or 275/75R18?
275/75R18 is taller by 2.17 inches (34.24" vs 32.07"). 275/65R18 is the same width.
Can I replace 275/65R18 with 275/75R18?
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 275/75R18 change my speedometer?
When your speedometer reads 60 mph with 275/75R18 fitted (calibrated for 275/65R18), your real speed is 64.1 mph. Your odometer will under-count miles by about 6.8%.
Will 275/75R18 lift my vehicle?
Ride height changes by half the diameter difference: +1.08 inches of ground clearance at the axle.

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