245/40R18 vs 285/35R18

Q: Can I replace 245/40R18 with 285/35R18?

285/35R18 is a safe swap for 245/40R18 by the usual ±3% rule: the diameter differs by +0.54%.

285/35R18 is a safe swap for 245/40R18 by the usual ±3% rule: the diameter differs by +0.54%.

245/40R18 25.72" · 285/35R18 25.85" · drawn to scale

Side by side

	245/40R18	285/35R18	Difference
Overall diameter	25.72"	25.85"	+0.14" (+0.54%)
Section width	245 mm	285 mm	+40 mm
Sidewall	3.86"	3.93"	+0.07"
Rim	18"	18"	same
Circumference	80.8"	81.2"	+0.4"
Revs per mile	784	780	-4
Ride height	—	—	+0.07"
Speedometer reads 60 mph	60.0	60.3	+0.3 mph

Speedometer and odometer

With 285/35R18 on a car calibrated for 245/40R18, 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 245/40R18

Questions

Can I replace 245/40R18 with 285/35R18?

285/35R18 is a safe swap for 245/40R18 by the usual ±3% rule: the diameter differs by +0.54%.

What's the difference between 245/40R18 and 285/35R18?

285/35R18 is 0.14" taller and 40 mm wider; the sidewall is +0.07". At an indicated 60 mph you'd actually be doing 60.3 mph.

Will 285/35R18 fit on 245/40R18 wheels?

Both use a 18" rim, so the wheel diameter matches; check the wheel's width range for a 285 mm tire and the fender clearance.