285/40R20 vs 295/35R21Tire Size Comparison

Safe

The 0.5% diameter difference is within the accepted 3% tolerance.

285/40R20736mm dia295/35R21740mm dia+1.9mm

Comparison Details

Overall Diameter736.0 vs 739.9 mm (+3.9 mm)
Diameter Difference+0.53%
Section Width285 vs 295 mm (+10 mm)
Sidewall Height114.0 vs 103.3 mm (-10.7 mm)
Circumference2312.2 vs 2324.5 mm
Clearance Change+1.9 mm
Speedometer Error+0.53%
Revs/Mile696 vs 692

Speedometer Correction

When switching from 285/40R20 to 295/35R21, your speedometer will differ from actual speed.

SpeedometerActual SpeedDifference
30 km/h30.2 km/h+0.2 km/h
40 km/h40.2 km/h+0.2 km/h
50 km/h50.3 km/h+0.3 km/h
60 km/h60.3 km/h+0.3 km/h
70 km/h70.4 km/h+0.4 km/h
80 km/h80.4 km/h+0.4 km/h
90 km/h90.5 km/h+0.5 km/h
100 km/h100.5 km/h+0.5 km/h
110 km/h110.6 km/h+0.6 km/h
120 km/h120.6 km/h+0.6 km/h
130 km/h130.7 km/h+0.7 km/h

Individual Tire Size Details

285/40R20
Full specifications, compatible vehicles, and alternatives
295/35R21
Full specifications, compatible vehicles, and alternatives

Practical Guidance

Switching from 285/40R20 to 295/35R21 is within the industry-accepted 3% diameter tolerance. Your speedometer, ABS, and traction control should function normally. Note: these sizes require different rim diameters (20" vs 21"), so you will need different wheels.

The 3% diameter tolerance is a widely accepted industry guideline referenced by the ETRTO and most vehicle manufacturers. When in doubt, consult your vehicle's owner's manual or a qualified tire professional. For U.S. tire safety standards and recalls, see the NHTSA Tire Safety page.

Frequently Asked Questions

Safe. The overall diameter differs by 0.53%, width changes by 10mm.

Speedometer error will be 0.53%. At an indicated 100 km/h, actual speed is about 100.5 km/h.

Ground clearance changes by +1.9mm per side.