What is the diameter difference between 255/35R20 and 265/30R20?

255/35R20 has an overall diameter of 27.03 inches (687 mm). 265/30R20 is 26.26 inches (667 mm). That's a 0.77 inch (20 mm) difference — 265/30R20 is shorter.

Will 265/30R20 cause speedometer error on a car fitted with 255/35R20?

Swapping 255/35R20 for 265/30R20 produces a speedometer error of about 2.8%. Your speedometer will read higher than your actual speed — a 60 mph indicated reading is really 58.3 mph. Anything under 3% is usually acceptable without recalibration.

How many revolutions per mile does each size do?

255/35R20 turns 746 revs per mile. 265/30R20 turns 768 revs per mile. Taller tyres turn fewer times per mile, which lowers effective final-drive ratio.

What's the sidewall height difference?

255/35R20 has a sidewall of 89 mm (3.51 in). 265/30R20 sidewall is 80 mm (3.13 in). Lower-profile sidewalls give sharper steering response but less bump compliance.

Is 265/30R20 a safe plus-size upgrade from 255/35R20?

A plus-size upgrade is considered safe when overall diameter stays within ±3% — here the difference is 2.8%. This swap is within the typical safe range; speedometer and ABS calibration should remain close to factory.

Tire size comparison

255/35R20 vs 265/30R20

Overall diameter, sidewall, revs per mile, and speedometer error — 255/35R20 is the taller tire, with a 2.8% speedo delta when swapping.

255/35R20

27.03in

687 mm overall diameter

265/30R20

26.26in

667 mm overall diameter

Diameter Δ

0.77 in

Speedo error

2.8%

255/35R20 revs/mi

746

265/30R20 revs/mi

768

Within the ±3% overall-diameter band usually considered safe for plus-sizing — speedometer and ABS calibration should stay close to factory.

Full spec

Side by side

Metric	255/35R20	265/30R20
Section width	255 mm	265 mm
Aspect ratio	35	30
Wheel diameter	20″	20″
Sidewall height	89 mm	80 mm
Overall diameter	27.03 in (687 mm)	26.26 in (667 mm)
Circumference	84.91 in	82.5 in
Revolutions / mile	746	768

Other comparisons for these sizes

235/45R18 vs 255/35R20 245/40R18 vs 265/30R20 245/40R19 vs 255/35R20 255/35R19 vs 265/30R20 255/40R19 vs 255/35R20 265/35R19 vs 265/30R20 245/35R20 vs 255/35R20 255/30R20 vs 265/30R20 255/30R20 vs 255/35R20 255/35R20 vs 265/35R20

FAQ

Frequently asked

What is the diameter difference between 255/35R20 and 265/30R20?: 255/35R20 has an overall diameter of 27.03 inches (687 mm). 265/30R20 is 26.26 inches (667 mm). That's a 0.77 inch (20 mm) difference — 265/30R20 is shorter.
Will 265/30R20 cause speedometer error on a car fitted with 255/35R20?: Swapping 255/35R20 for 265/30R20 produces a speedometer error of about 2.8%. Your speedometer will read higher than your actual speed — a 60 mph indicated reading is really 58.3 mph. Anything under 3% is usually acceptable without recalibration.
How many revolutions per mile does each size do?: 255/35R20 turns 746 revs per mile. 265/30R20 turns 768 revs per mile. Taller tyres turn fewer times per mile, which lowers effective final-drive ratio.
What's the sidewall height difference?: 255/35R20 has a sidewall of 89 mm (3.51 in). 265/30R20 sidewall is 80 mm (3.13 in). Lower-profile sidewalls give sharper steering response but less bump compliance.
Is 265/30R20 a safe plus-size upgrade from 255/35R20?: A plus-size upgrade is considered safe when overall diameter stays within ±3% — here the difference is 2.8%. This swap is within the typical safe range; speedometer and ABS calibration should remain close to factory.