Tire Size Box

235/65R18 vs 235/75R18

235/75R18 compared with 235/65R18

+6.2% diameter, 0.0" width

235/75R18 is 31.88" tall vs 30.03". More than the 3% rule of thumb, so check carefully before switching.

30.0"18" rim6.0"9.3" wide
235/65R18 (solid) compared with 235/75R18 (dashed outline), drawn to scale

With 235/75R18 tires, when your speedometer says 60 mph you are really going

63.7 mph

235/75R18 is +1.85 inches (+6.2%) in overall diameter. That is more than the 3% most shops and makers recommend.

235/65R18235/75R18Difference%
Overall diameter30.03"31.88"+1.85"+6.2%
Section width9.25"9.25"0.00"0.0%
Sidewall height6.01"6.94"+0.93"+15.4%
Circumference94.33"100.15"+5.81"+6.2%
Revolutions per mile671.7632.7−39.0−5.8%

Speedometer difference

If your vehicle came with 235/65R18 and you fit 235/75R18, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph21.2 mph+1.2 mph
30 mph31.8 mph+1.8 mph
40 mph42.5 mph+2.5 mph
50 mph53.1 mph+3.1 mph
60 mph63.7 mph+3.7 mph
65 mph69.0 mph+4.0 mph
70 mph74.3 mph+4.3 mph
75 mph79.6 mph+4.6 mph
80 mph84.9 mph+4.9 mph

Each size on its own

Questions

Which is bigger, 235/65R18 or 235/75R18?
235/75R18 is taller by 1.85 inches (31.88" vs 30.03"). 235/65R18 is the same width.
Can I replace 235/65R18 with 235/75R18?
It is not recommended without checking carefully. The diameter difference is +6.2%, 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 235/75R18 change my speedometer?
When your speedometer reads 60 mph with 235/75R18 fitted (calibrated for 235/65R18), your real speed is 63.7 mph. Your odometer will under-count miles by about 6.2%.
Will 235/75R18 lift my vehicle?
Ride height changes by half the diameter difference: +0.93 inches of ground clearance at the axle.

Other comparisons