265/40R20 vs 245/45R20

Q: Can I replace 265/40R20 with 245/45R20?

245/45R20 is a safe swap for 265/40R20 by the usual ±3% rule: the diameter differs by +1.18%.

245/45R20 is a safe swap for 265/40R20 by the usual ±3% rule: the diameter differs by +1.18%.

265/40R20 28.35" · 245/45R20 28.68" · drawn to scale

Side by side

	265/40R20	245/45R20	Difference
Overall diameter	28.35"	28.68"	+0.33" (+1.18%)
Section width	265 mm	245 mm	-20 mm
Sidewall	4.17"	4.34"	+0.17"
Rim	20"	20"	same
Circumference	89.1"	90.1"	+1.1"
Revs per mile	711	703	-8
Ride height	—	—	+0.17"
Speedometer reads 60 mph	60.0	60.7	+0.7 mph

Speedometer and odometer

With 245/45R20 on a car calibrated for 265/40R20, the speedometer reads 59.3 mph when you're really doing 60, and the odometer under-counts by 1.2%.

Speedo shows	Actual speed
30 mph	30.4 mph
45 mph	45.5 mph
60 mph	60.7 mph
70 mph	70.8 mph
80 mph	80.9 mph

Other sizes close to 265/40R20

Questions

Can I replace 265/40R20 with 245/45R20?

245/45R20 is a safe swap for 265/40R20 by the usual ±3% rule: the diameter differs by +1.18%.

What's the difference between 265/40R20 and 245/45R20?

245/45R20 is 0.33" taller and 20 mm narrower; the sidewall is +0.17". At an indicated 60 mph you'd actually be doing 60.7 mph.

Will 245/45R20 fit on 265/40R20 wheels?

Both use a 20" rim, so the wheel diameter matches; check the wheel's width range for a 245 mm tire and the fender clearance.