275/35R20 vs 235/45R20

Q: Can I replace 275/35R20 with 235/45R20?

235/45R20 is a safe swap for 275/35R20 by the usual ±3% rule: the diameter differs by +2.71%.

235/45R20 is a safe swap for 275/35R20 by the usual ±3% rule: the diameter differs by +2.71%.

275/35R20 27.58" · 235/45R20 28.33" · drawn to scale

Side by side

	275/35R20	235/45R20	Difference
Overall diameter	27.58"	28.33"	+0.75" (+2.71%)
Section width	275 mm	235 mm	-40 mm
Sidewall	3.79"	4.16"	+0.37"
Rim	20"	20"	same
Circumference	86.6"	89.0"	+2.4"
Revs per mile	731	712	-19
Ride height	—	—	+0.37"
Speedometer reads 60 mph	60.0	61.6	+1.6 mph

Speedometer and odometer

With 235/45R20 on a car calibrated for 275/35R20, the speedometer reads 58.4 mph when you're really doing 60, and the odometer under-counts by 2.7%.

Speedo shows	Actual speed
30 mph	30.8 mph
45 mph	46.2 mph
60 mph	61.6 mph
70 mph	71.9 mph
80 mph	82.2 mph

Other sizes close to 275/35R20

Questions

Can I replace 275/35R20 with 235/45R20?

235/45R20 is a safe swap for 275/35R20 by the usual ±3% rule: the diameter differs by +2.71%.

What's the difference between 275/35R20 and 235/45R20?

235/45R20 is 0.75" taller and 40 mm narrower; the sidewall is +0.37". At an indicated 60 mph you'd actually be doing 61.6 mph.

Will 235/45R20 fit on 275/35R20 wheels?

Both use a 20" rim, so the wheel diameter matches; check the wheel's width range for a 235 mm tire and the fender clearance.