What is the diameter difference between 275/35R20 and 285/30R20?

275/35R20 has an overall diameter of 27.58 inches (701 mm). 285/30R20 is 26.73 inches (679 mm). That's a 0.85 inch (22 mm) difference — 285/30R20 is shorter.

Will 285/30R20 cause speedometer error on a car fitted with 275/35R20?

Swapping 275/35R20 for 285/30R20 produces a speedometer error of about 3.1%. Your speedometer will read higher than your actual speed — a 60 mph indicated reading is really 58.2 mph. Anything under 3% is usually acceptable without recalibration.

How many revolutions per mile does each size do?

275/35R20 turns 731 revs per mile. 285/30R20 turns 754 revs per mile. Taller tyres turn fewer times per mile, which lowers effective final-drive ratio.

What's the sidewall height difference?

275/35R20 has a sidewall of 96 mm (3.79 in). 285/30R20 sidewall is 86 mm (3.37 in). Lower-profile sidewalls give sharper steering response but less bump compliance.

Is 285/30R20 a safe plus-size upgrade from 275/35R20?

A plus-size upgrade is considered safe when overall diameter stays within ±3% — here the difference is 3.1%. This swap is outside the typical ±3% safe range and may require speedometer recalibration or affect ABS / traction control behaviour.

Tire size comparison

275/35R20 vs 285/30R20

Overall diameter, sidewall, revs per mile, and speedometer error — 275/35R20 is the taller tire, with a 3.1% speedo delta when swapping.

275/35R20

27.58in

701 mm overall diameter

285/30R20

26.73in

679 mm overall diameter

Diameter Δ

0.85 in

Speedo error

3.1%

275/35R20 revs/mi

731

285/30R20 revs/mi

754

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	275/35R20	285/30R20
Section width	275 mm	285 mm
Aspect ratio	35	30
Wheel diameter	20″	20″
Sidewall height	96 mm	86 mm
Overall diameter	27.58 in (701 mm)	26.73 in (679 mm)
Circumference	86.64 in	83.98 in
Revolutions / mile	731	754

Other comparisons for these sizes

255/45R18 vs 275/35R20 275/35R19 vs 285/30R20 255/35R20 vs 275/35R20 265/30R20 vs 285/30R20 265/35R20 vs 275/35R20 275/30R20 vs 285/30R20 275/30R20 vs 275/35R20 275/35R20 vs 285/30R21 275/35R20 vs 275/30R21 275/35R20 vs 285/35R20

FAQ

Frequently asked

What is the diameter difference between 275/35R20 and 285/30R20?: 275/35R20 has an overall diameter of 27.58 inches (701 mm). 285/30R20 is 26.73 inches (679 mm). That's a 0.85 inch (22 mm) difference — 285/30R20 is shorter.
Will 285/30R20 cause speedometer error on a car fitted with 275/35R20?: Swapping 275/35R20 for 285/30R20 produces a speedometer error of about 3.1%. Your speedometer will read higher than your actual speed — a 60 mph indicated reading is really 58.2 mph. Anything under 3% is usually acceptable without recalibration.
How many revolutions per mile does each size do?: 275/35R20 turns 731 revs per mile. 285/30R20 turns 754 revs per mile. Taller tyres turn fewer times per mile, which lowers effective final-drive ratio.
What's the sidewall height difference?: 275/35R20 has a sidewall of 96 mm (3.79 in). 285/30R20 sidewall is 86 mm (3.37 in). Lower-profile sidewalls give sharper steering response but less bump compliance.
Is 285/30R20 a safe plus-size upgrade from 275/35R20?: A plus-size upgrade is considered safe when overall diameter stays within ±3% — here the difference is 3.1%. This swap is outside the typical ±3% safe range and may require speedometer recalibration or affect ABS / traction control behaviour.