245/40R19 vs 225/50R18

Q: Can I replace 245/40R19 with 225/50R18?

225/50R18 is a safe swap for 245/40R19 by the usual ±3% rule: the diameter differs by +0.53%.

225/50R18 is a safe swap for 245/40R19 by the usual ±3% rule: the diameter differs by +0.53%.

245/40R19 26.72" · 225/50R18 26.86" · drawn to scale

Side by side

	245/40R19	225/50R18	Difference
Overall diameter	26.72"	26.86"	+0.14" (+0.53%)
Section width	245 mm	225 mm	-20 mm
Sidewall	3.86"	4.43"	+0.57"
Rim	19"	18"	-1"
Circumference	83.9"	84.4"	+0.4"
Revs per mile	755	751	-4
Ride height	—	—	+0.07"
Speedometer reads 60 mph	60.0	60.3	+0.3 mph

Speedometer and odometer

With 225/50R18 on a car calibrated for 245/40R19, 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 245/40R19

Questions

Can I replace 245/40R19 with 225/50R18?

225/50R18 is a safe swap for 245/40R19 by the usual ±3% rule: the diameter differs by +0.53%.

What's the difference between 245/40R19 and 225/50R18?

225/50R18 is 0.14" taller and 20 mm narrower; the sidewall is +0.57". At an indicated 60 mph you'd actually be doing 60.3 mph.

Will 225/50R18 fit on 245/40R19 wheels?

No — 245/40R19 needs a 19" wheel and 225/50R18 a 18" wheel. This is a plus/minus-size swap that changes wheels too.