265/45R20 vs 275/40R21

Q: Can I replace 265/45R20 with 275/40R21?

275/40R21 is a safe swap for 265/45R20 by the usual ±3% rule: the diameter differs by +0.92%.

275/40R21 is a safe swap for 265/45R20 by the usual ±3% rule: the diameter differs by +0.92%.

265/45R20 29.39" · 275/40R21 29.66" · drawn to scale

Side by side

	265/45R20	275/40R21	Difference
Overall diameter	29.39"	29.66"	+0.27" (+0.92%)
Section width	265 mm	275 mm	+10 mm
Sidewall	4.69"	4.33"	-0.36"
Rim	20"	21"	+1"
Circumference	92.3"	93.2"	+0.9"
Revs per mile	686	680	-6
Ride height	—	—	+0.14"
Speedometer reads 60 mph	60.0	60.6	+0.6 mph

Speedometer and odometer

With 275/40R21 on a car calibrated for 265/45R20, the speedometer reads 59.5 mph when you're really doing 60, and the odometer under-counts by 0.9%.

Speedo shows	Actual speed
30 mph	30.3 mph
45 mph	45.4 mph
60 mph	60.6 mph
70 mph	70.6 mph
80 mph	80.7 mph

Other sizes close to 265/45R20

Questions

Can I replace 265/45R20 with 275/40R21?

275/40R21 is a safe swap for 265/45R20 by the usual ±3% rule: the diameter differs by +0.92%.

What's the difference between 265/45R20 and 275/40R21?

275/40R21 is 0.27" taller and 10 mm wider; the sidewall is -0.36". At an indicated 60 mph you'd actually be doing 60.6 mph.

Will 275/40R21 fit on 265/45R20 wheels?

No — 265/45R20 needs a 20" wheel and 275/40R21 a 21" wheel. This is a plus/minus-size swap that changes wheels too.