265/40R20 vs 255/45R20

Q: Can I replace 265/40R20 with 255/45R20?

255/45R20 is a safe swap for 265/40R20 by the usual ±3% rule: the diameter differs by +2.43%.

255/45R20 is a safe swap for 265/40R20 by the usual ±3% rule: the diameter differs by +2.43%.

265/40R20 28.35" · 255/45R20 29.04" · drawn to scale

Side by side

	265/40R20	255/45R20	Difference
Overall diameter	28.35"	29.04"	+0.69" (+2.43%)
Section width	265 mm	255 mm	-10 mm
Sidewall	4.17"	4.52"	+0.34"
Rim	20"	20"	same
Circumference	89.1"	91.2"	+2.2"
Revs per mile	711	695	-17
Ride height	—	—	+0.34"
Speedometer reads 60 mph	60.0	61.5	+1.5 mph

Speedometer and odometer

With 255/45R20 on a car calibrated for 265/40R20, the speedometer reads 58.6 mph when you're really doing 60, and the odometer under-counts by 2.4%.

Speedo shows	Actual speed
30 mph	30.7 mph
45 mph	46.1 mph
60 mph	61.5 mph
70 mph	71.7 mph
80 mph	81.9 mph

Other sizes close to 265/40R20

Questions

Can I replace 265/40R20 with 255/45R20?

255/45R20 is a safe swap for 265/40R20 by the usual ±3% rule: the diameter differs by +2.43%.

What's the difference between 265/40R20 and 255/45R20?

255/45R20 is 0.69" taller and 10 mm narrower; the sidewall is +0.34". At an indicated 60 mph you'd actually be doing 61.5 mph.

Will 255/45R20 fit on 265/40R20 wheels?

Both use a 20" rim, so the wheel diameter matches; check the wheel's width range for a 255 mm tire and the fender clearance.