What is the diameter difference between 285/30R20 and 285/35R20?

285/30R20 has an overall diameter of 26.73 inches (679 mm). 285/35R20 is 27.85 inches (708 mm). That's a 1.12 inch (29 mm) difference — 285/35R20 is taller.

Will 285/35R20 cause speedometer error on a car fitted with 285/30R20?

Swapping 285/30R20 for 285/35R20 produces a speedometer error of about 4.2%. Your speedometer will read lower than your actual speed — a 60 mph indicated reading is really 62.5 mph. Anything under 3% is usually acceptable without recalibration.

How many revolutions per mile does each size do?

285/30R20 turns 754 revs per mile. 285/35R20 turns 724 revs per mile. Taller tyres turn fewer times per mile, which lowers effective final-drive ratio.

What's the sidewall height difference?

285/30R20 has a sidewall of 86 mm (3.37 in). 285/35R20 sidewall is 100 mm (3.93 in). Lower-profile sidewalls give sharper steering response but less bump compliance.

Is 285/35R20 a safe plus-size upgrade from 285/30R20?

A plus-size upgrade is considered safe when overall diameter stays within ±3% — here the difference is 4.2%. This swap is outside the typical ±3% safe range and may require speedometer recalibration or affect ABS / traction control behaviour.

Tire size comparison

285/30R20 vs 285/35R20

Overall diameter, sidewall, revs per mile, and speedometer error — 285/35R20 is the taller tire, with a 4.2% speedo delta when swapping.

285/30R20

26.73in

679 mm overall diameter

285/35R20

27.85in

708 mm overall diameter

Diameter Δ

1.12 in

Speedo error

4.2%

285/30R20 revs/mi

754

285/35R20 revs/mi

724

Outside the typical ±3% safe plus-size band — you may want speedometer recalibration, and this change can affect ABS or traction control behaviour.

Full spec

Side by side

Metric	285/30R20	285/35R20
Section width	285 mm	285 mm
Aspect ratio	30	35
Wheel diameter	20″	20″
Sidewall height	86 mm	100 mm
Overall diameter	26.73 in (679 mm)	27.85 in (708 mm)
Circumference	83.98 in	87.51 in
Revolutions / mile	754	724

Other comparisons for these sizes

275/35R19 vs 285/30R20 265/30R20 vs 285/30R20 265/35R20 vs 285/35R20 275/30R20 vs 285/30R20 275/35R20 vs 285/35R20 275/35R20 vs 285/30R20 285/30R20 vs 295/30R20 285/30R20 vs 305/30R20 285/35R20 vs 295/30R21 285/35R20 vs 285/30R21

FAQ

Frequently asked

What is the diameter difference between 285/30R20 and 285/35R20?: 285/30R20 has an overall diameter of 26.73 inches (679 mm). 285/35R20 is 27.85 inches (708 mm). That's a 1.12 inch (29 mm) difference — 285/35R20 is taller.
Will 285/35R20 cause speedometer error on a car fitted with 285/30R20?: Swapping 285/30R20 for 285/35R20 produces a speedometer error of about 4.2%. Your speedometer will read lower than your actual speed — a 60 mph indicated reading is really 62.5 mph. Anything under 3% is usually acceptable without recalibration.
How many revolutions per mile does each size do?: 285/30R20 turns 754 revs per mile. 285/35R20 turns 724 revs per mile. Taller tyres turn fewer times per mile, which lowers effective final-drive ratio.
What's the sidewall height difference?: 285/30R20 has a sidewall of 86 mm (3.37 in). 285/35R20 sidewall is 100 mm (3.93 in). Lower-profile sidewalls give sharper steering response but less bump compliance.
Is 285/35R20 a safe plus-size upgrade from 285/30R20?: A plus-size upgrade is considered safe when overall diameter stays within ±3% — here the difference is 4.2%. This swap is outside the typical ±3% safe range and may require speedometer recalibration or affect ABS / traction control behaviour.