What is the diameter difference between 255/35R21 and 265/35R21?

255/35R21 has an overall diameter of 28.03 inches (712 mm). 265/35R21 is 28.3 inches (719 mm). That's a 0.28 inch (7 mm) difference — 265/35R21 is taller.

Will 265/35R21 cause speedometer error on a car fitted with 255/35R21?

Swapping 255/35R21 for 265/35R21 produces a speedometer error of about 1%. Your speedometer will read lower than your actual speed — a 60 mph indicated reading is really 60.6 mph. Anything under 3% is usually acceptable without recalibration.

How many revolutions per mile does each size do?

255/35R21 turns 720 revs per mile. 265/35R21 turns 713 revs per mile. Taller tyres turn fewer times per mile, which lowers effective final-drive ratio.

What's the sidewall height difference?

255/35R21 has a sidewall of 89 mm (3.51 in). 265/35R21 sidewall is 93 mm (3.65 in). Lower-profile sidewalls give sharper steering response but less bump compliance.

Is 265/35R21 a safe plus-size upgrade from 255/35R21?

A plus-size upgrade is considered safe when overall diameter stays within ±3% — here the difference is 1%. This swap is within the typical safe range; speedometer and ABS calibration should remain close to factory.

Tire size comparison

255/35R21 vs 265/35R21

Overall diameter, sidewall, revs per mile, and speedometer error — 265/35R21 is the taller tire, with a 1% speedo delta when swapping.

255/35R21

28.03in

712 mm overall diameter

265/35R21

28.3in

719 mm overall diameter

Diameter Δ

0.28 in

Speedo error

255/35R21 revs/mi

720

265/35R21 revs/mi

713

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	255/35R21	265/35R21
Section width	255 mm	265 mm
Aspect ratio	35	35
Wheel diameter	21″	21″
Sidewall height	89 mm	93 mm
Overall diameter	28.03 in (712 mm)	28.3 in (719 mm)
Circumference	88.05 in	88.92 in
Revolutions / mile	720	713

Other comparisons for these sizes

245/45R19 vs 265/35R21 255/35R21 vs 275/35R21 265/35R21 vs 275/35R21 265/35R21 vs 275/30R21

FAQ

Frequently asked

What is the diameter difference between 255/35R21 and 265/35R21?: 255/35R21 has an overall diameter of 28.03 inches (712 mm). 265/35R21 is 28.3 inches (719 mm). That's a 0.28 inch (7 mm) difference — 265/35R21 is taller.
Will 265/35R21 cause speedometer error on a car fitted with 255/35R21?: Swapping 255/35R21 for 265/35R21 produces a speedometer error of about 1%. Your speedometer will read lower than your actual speed — a 60 mph indicated reading is really 60.6 mph. Anything under 3% is usually acceptable without recalibration.
How many revolutions per mile does each size do?: 255/35R21 turns 720 revs per mile. 265/35R21 turns 713 revs per mile. Taller tyres turn fewer times per mile, which lowers effective final-drive ratio.
What's the sidewall height difference?: 255/35R21 has a sidewall of 89 mm (3.51 in). 265/35R21 sidewall is 93 mm (3.65 in). Lower-profile sidewalls give sharper steering response but less bump compliance.
Is 265/35R21 a safe plus-size upgrade from 255/35R21?: A plus-size upgrade is considered safe when overall diameter stays within ±3% — here the difference is 1%. This swap is within the typical safe range; speedometer and ABS calibration should remain close to factory.