285/65R18 vs 275/65R18

285/65R18 is 0.5" taller than 275/65R18 (1.6%)

Diameter difference−1.57%diameter 32.59" → 32.07"
285/65R18275/65R18
285/65R18275/65R18Difference
Overall diameter32.59"32.07"−0.51"
Section width11.22"10.83"−0.39"
Sidewall height7.29"7.04"−0.26"
Circumference102.4"100.8"−1.6"
Revolutions per mile619629+10
Wheel diameter18"18"±0"

Speedometer

ShowsActualDiff
30 mph29.5 mph−0.5
45 mph44.3 mph−0.7
60 mph59.1 mph−0.9
70 mph68.9 mph−1.1
80 mph78.7 mph−1.3

Gear ratio to match

CurrentEquivalent
3.423.37
3.553.49
3.733.67
4.104.04

275/65R18 is 0.51" shorter than 285/65R18, a −1.57% change in diameter, inside the 3% range most shops treat as a safe swap.

Ground clearance changes by 0.26" (half the diameter change), and the tire needs 0.26" less room above it.

285/65R18 is 0.39" wider. On the same wheel offset about half of that, 0.20", moves toward the suspension and half toward the fender.

Both fit a 18" wheel; the sidewall is 0.26" shorter on 275/65R18.

Details: 285/65R18 in inches · 275/65R18 in inches · change sizes in the calculator

FAQ

What is the difference between 285/65R18 and 275/65R18?

275/65R18 is 0.51" shorter (−1.57%) and 0.39" narrower than 285/65R18.

Will 275/65R18 change my speedometer?

Yes, by −1.57%. When the speedometer shows 60 mph you would be going 59.1 mph.

Can I replace 285/65R18 with 275/65R18?

Often yes: the diameter change of −1.6% is within the common 3% guideline. Check the load index, speed rating and clearance.