245/60R20 vs 275/50R21

Q: Can I replace 245/60R20 with 275/50R21?

275/50R21 is a safe swap for 245/60R20 by the usual ±3% rule: the diameter differs by +0.80%.

275/50R21 is a safe swap for 245/60R20 by the usual ±3% rule: the diameter differs by +0.80%.

245/60R20 31.57" · 275/50R21 31.83" · drawn to scale

Side by side

	245/60R20	275/50R21	Difference
Overall diameter	31.57"	31.83"	+0.25" (+0.80%)
Section width	245 mm	275 mm	+30 mm
Sidewall	5.79"	5.41"	-0.37"
Rim	20"	21"	+1"
Circumference	99.2"	100.0"	+0.8"
Revs per mile	639	634	-5
Ride height	—	—	+0.13"
Speedometer reads 60 mph	60.0	60.5	+0.5 mph

Speedometer and odometer

With 275/50R21 on a car calibrated for 245/60R20, 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	45.4 mph
60 mph	60.5 mph
70 mph	70.6 mph
80 mph	80.6 mph

Other sizes close to 245/60R20

Questions

Can I replace 245/60R20 with 275/50R21?

275/50R21 is a safe swap for 245/60R20 by the usual ±3% rule: the diameter differs by +0.80%.

What's the difference between 245/60R20 and 275/50R21?

275/50R21 is 0.25" taller and 30 mm wider; the sidewall is -0.37". At an indicated 60 mph you'd actually be doing 60.5 mph.

Will 275/50R21 fit on 245/60R20 wheels?

No — 245/60R20 needs a 20" wheel and 275/50R21 a 21" wheel. This is a plus/minus-size swap that changes wheels too.