235/45R18 vs 215/50R18

Q: Can I replace 235/45R18 with 215/50R18?

215/50R18 is a safe swap for 235/45R18 by the usual ±3% rule: the diameter differs by +0.52%.

215/50R18 is a safe swap for 235/45R18 by the usual ±3% rule: the diameter differs by +0.52%.

235/45R18 26.33" · 215/50R18 26.46" · drawn to scale

Side by side

	235/45R18	215/50R18	Difference
Overall diameter	26.33"	26.46"	+0.14" (+0.52%)
Section width	235 mm	215 mm	-20 mm
Sidewall	4.16"	4.23"	+0.07"
Rim	18"	18"	same
Circumference	82.7"	83.1"	+0.4"
Revs per mile	766	762	-4
Ride height	—	—	+0.07"
Speedometer reads 60 mph	60.0	60.3	+0.3 mph

Speedometer and odometer

With 215/50R18 on a car calibrated for 235/45R18, the speedometer reads 59.7 mph when you're really doing 60, and the odometer under-counts by 0.5%.

Speedo shows	Actual speed
30 mph	30.2 mph
45 mph	45.2 mph
60 mph	60.3 mph
70 mph	70.4 mph
80 mph	80.4 mph

Other sizes close to 235/45R18

Questions

Can I replace 235/45R18 with 215/50R18?

215/50R18 is a safe swap for 235/45R18 by the usual ±3% rule: the diameter differs by +0.52%.

What's the difference between 235/45R18 and 215/50R18?

215/50R18 is 0.14" taller and 20 mm narrower; the sidewall is +0.07". At an indicated 60 mph you'd actually be doing 60.3 mph.

Will 215/50R18 fit on 235/45R18 wheels?

Both use a 18" rim, so the wheel diameter matches; check the wheel's width range for a 215 mm tire and the fender clearance.