275/70R18 vs 285/75R18
285/75R18 is 1.67 in (42.5 mm) taller than 275/70R18 (+5.05%). Ground clearance at the axle changes by about +0.84 in. At an indicated 60 mph you would really be going 63.0 mph. That is more than a 3% change in diameter, so check clearance, gearing and speedometer calibration.
Side by side
Solid blue = 275/70R18, dashed orange = 285/75R18. Drawn to scale.
| Measurement | A275/70R18 | B285/75R18 | Change |
|---|---|---|---|
| Overall diameter | 33.16 in842.2 mm | 34.83 in884.7 mm | +1.67 in+42.5 mm+5.05% |
| Section width | 10.83 in275.0 mm | 11.22 in285.0 mm | +0.39 in+10.0 mm+3.64% |
| Sidewall height | 7.58 in192.5 mm | 8.42 in213.8 mm | +0.84 in+21.3 mm+11.04% |
| Circumference | 104.17 in2645.8 mm | 109.42 in2779.4 mm | +5.26 in+133.5 mm+5.05% |
| Aspect ratio | 70.0% | 75.0% | +5.0 pts |
| Revolutions per mile | 608.3 | 579.0 | -29.2-4.80% |
Open this comparison in the calculator to change either size.
Speedometer error
| Speedometer shows | Actual speed | Change |
|---|---|---|
| 20 mph | 21.0 mph | +1.0 mph |
| 30 mph | 31.5 mph | +1.5 mph |
| 40 mph | 42.0 mph | +2.0 mph |
| 50 mph | 52.5 mph | +2.5 mph |
| 60 mph | 63.0 mph | +3.0 mph |
| 70 mph | 73.5 mph | +3.5 mph |
| 80 mph | 84.0 mph | +4.0 mph |
What changes
285/75R18 is 0.39 in (10.0 mm) wider, and its sidewall is 0.84 in taller. Both mount on a 18 in wheel.
Each mile, 275/70R18 turns about 608 times and 285/75R18 about 579 times. Fewer turns per mile means the speedometer and odometer read low by roughly 5.0% unless they are recalibrated, and the effective final drive ratio gets taller, which can feel like slightly less acceleration.
These figures are calculated from the size alone. Actual tires vary by brand and model, and fitment depends on your wheels and suspension, so check with a tire shop before buying.