305/70R16 vs 255/80R17

Q: Can I replace 305/70R16 with 255/80R17?

255/80R17 is a safe swap for 305/70R16 by the usual ±3% rule: the diameter differs by +0.77%.

255/80R17 is a safe swap for 305/70R16 by the usual ±3% rule: the diameter differs by +0.77%.

305/70R16 32.81" · 255/80R17 33.06" · drawn to scale

Side by side

	305/70R16	255/80R17	Difference
Overall diameter	32.81"	33.06"	+0.25" (+0.77%)
Section width	305 mm	255 mm	-50 mm
Sidewall	8.41"	8.03"	-0.37"
Rim	16"	17"	+1"
Circumference	103.1"	103.9"	+0.8"
Revs per mile	615	610	-5
Ride height	—	—	+0.13"
Speedometer reads 60 mph	60.0	60.5	+0.5 mph

Speedometer and odometer

With 255/80R17 on a car calibrated for 305/70R16, the speedometer reads 59.5 mph when you're really doing 60, and the odometer under-counts by 0.8%.

Speedo shows	Actual speed
30 mph	30.2 mph
45 mph	45.3 mph
60 mph	60.5 mph
70 mph	70.5 mph
80 mph	80.6 mph

Other sizes close to 305/70R16

Questions

Can I replace 305/70R16 with 255/80R17?

255/80R17 is a safe swap for 305/70R16 by the usual ±3% rule: the diameter differs by +0.77%.

What's the difference between 305/70R16 and 255/80R17?

255/80R17 is 0.25" taller and 50 mm narrower; the sidewall is -0.37". At an indicated 60 mph you'd actually be doing 60.5 mph.

Will 255/80R17 fit on 305/70R16 wheels?

No — 305/70R16 needs a 16" wheel and 255/80R17 a 17" wheel. This is a plus/minus-size swap that changes wheels too.