285/35R20 vs 275/40R20

Q: Can I replace 285/35R20 with 275/40R20?

275/40R20 is a safe swap for 285/35R20 by the usual ±3% rule: the diameter differs by +2.90%.

275/40R20 is a safe swap for 285/35R20 by the usual ±3% rule: the diameter differs by +2.90%.

285/35R20 27.85" · 275/40R20 28.66" · drawn to scale

Side by side

	285/35R20	275/40R20	Difference
Overall diameter	27.85"	28.66"	+0.81" (+2.90%)
Section width	285 mm	275 mm	-10 mm
Sidewall	3.93"	4.33"	+0.40"
Rim	20"	20"	same
Circumference	87.5"	90.0"	+2.5"
Revs per mile	724	704	-20
Ride height	—	—	+0.40"
Speedometer reads 60 mph	60.0	61.7	+1.7 mph

Speedometer and odometer

With 275/40R20 on a car calibrated for 285/35R20, the speedometer reads 58.3 mph when you're really doing 60, and the odometer under-counts by 2.9%.

Speedo shows	Actual speed
30 mph	30.9 mph
45 mph	46.3 mph
60 mph	61.7 mph
70 mph	72.0 mph
80 mph	82.3 mph

Other sizes close to 285/35R20

Questions

Can I replace 285/35R20 with 275/40R20?

275/40R20 is a safe swap for 285/35R20 by the usual ±3% rule: the diameter differs by +2.90%.

What's the difference between 285/35R20 and 275/40R20?

275/40R20 is 0.81" taller and 10 mm narrower; the sidewall is +0.40". At an indicated 60 mph you'd actually be doing 61.7 mph.

Will 275/40R20 fit on 285/35R20 wheels?

Both use a 20" rim, so the wheel diameter matches; check the wheel's width range for a 275 mm tire and the fender clearance.