275/55R17 vs 255/55R18

Q: Can I replace 275/55R17 with 255/55R18?

255/55R18 is a safe swap for 275/55R17 by the usual ±3% rule: the diameter differs by +0.46%.

255/55R18 is a safe swap for 275/55R17 by the usual ±3% rule: the diameter differs by +0.46%.

275/55R17 28.91" · 255/55R18 29.04" · drawn to scale

Side by side

	275/55R17	255/55R18	Difference
Overall diameter	28.91"	29.04"	+0.13" (+0.46%)
Section width	275 mm	255 mm	-20 mm
Sidewall	5.95"	5.52"	-0.43"
Rim	17"	18"	+1"
Circumference	90.8"	91.2"	+0.4"
Revs per mile	698	694	-3
Ride height	—	—	+0.07"
Speedometer reads 60 mph	60.0	60.3	+0.3 mph

Speedometer and odometer

With 255/55R18 on a car calibrated for 275/55R17, the speedometer reads 59.7 mph when you're really doing 60, and the odometer under-counts by 0.5%.

Speedo shows	Actual speed
30 mph	30.1 mph
45 mph	45.2 mph
60 mph	60.3 mph
70 mph	70.3 mph
80 mph	80.4 mph

Other sizes close to 275/55R17

Questions

Can I replace 275/55R17 with 255/55R18?

255/55R18 is a safe swap for 275/55R17 by the usual ±3% rule: the diameter differs by +0.46%.

What's the difference between 275/55R17 and 255/55R18?

255/55R18 is 0.13" taller and 20 mm narrower; the sidewall is -0.43". At an indicated 60 mph you'd actually be doing 60.3 mph.

Will 255/55R18 fit on 275/55R17 wheels?

No — 275/55R17 needs a 17" wheel and 255/55R18 a 18" wheel. This is a plus/minus-size swap that changes wheels too.