What is the diameter difference between 265/35R21 and 275/30R21?

265/35R21 has an overall diameter of 28.3 inches (719 mm). 275/30R21 is 27.5 inches (698 mm). That's a 0.81 inch (21 mm) difference — 275/30R21 is shorter.

Will 275/30R21 cause speedometer error on a car fitted with 265/35R21?

Swapping 265/35R21 for 275/30R21 produces a speedometer error of about 2.9%. 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?

265/35R21 turns 713 revs per mile. 275/30R21 turns 733 revs per mile. Taller tyres turn fewer times per mile, which lowers effective final-drive ratio.

What's the sidewall height difference?

265/35R21 has a sidewall of 93 mm (3.65 in). 275/30R21 sidewall is 83 mm (3.25 in). Lower-profile sidewalls give sharper steering response but less bump compliance.

Is 275/30R21 a safe plus-size upgrade from 265/35R21?

A plus-size upgrade is considered safe when overall diameter stays within ±3% — here the difference is 2.9%. This swap is within the typical safe range; speedometer and ABS calibration should remain close to factory.

Tire size comparison

265/35R21 vs 275/30R21

Overall diameter, sidewall, revs per mile, and speedometer error — 265/35R21 is the taller tire, with a 2.9% speedo delta when swapping.

265/35R21

28.3in

719 mm overall diameter

275/30R21

27.5in

698 mm overall diameter

Diameter Δ

0.81 in

Speedo error

2.9%

265/35R21 revs/mi

713

275/30R21 revs/mi

733

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	265/35R21	275/30R21
Section width	265 mm	275 mm
Aspect ratio	35	30
Wheel diameter	21″	21″
Sidewall height	93 mm	83 mm
Overall diameter	28.3 in (719 mm)	27.5 in (698 mm)
Circumference	88.92 in	86.38 in
Revolutions / mile	713	733

Other comparisons for these sizes

245/45R19 vs 265/35R21 255/40R19 vs 275/30R21 265/35R20 vs 275/30R21 275/35R20 vs 275/30R21 255/35R21 vs 265/35R21 265/35R21 vs 275/35R21 275/30R21 vs 285/30R21 275/30R21 vs 295/30R21 275/30R21 vs 275/35R21

FAQ

Frequently asked

What is the diameter difference between 265/35R21 and 275/30R21?: 265/35R21 has an overall diameter of 28.3 inches (719 mm). 275/30R21 is 27.5 inches (698 mm). That's a 0.81 inch (21 mm) difference — 275/30R21 is shorter.
Will 275/30R21 cause speedometer error on a car fitted with 265/35R21?: Swapping 265/35R21 for 275/30R21 produces a speedometer error of about 2.9%. 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?: 265/35R21 turns 713 revs per mile. 275/30R21 turns 733 revs per mile. Taller tyres turn fewer times per mile, which lowers effective final-drive ratio.
What's the sidewall height difference?: 265/35R21 has a sidewall of 93 mm (3.65 in). 275/30R21 sidewall is 83 mm (3.25 in). Lower-profile sidewalls give sharper steering response but less bump compliance.
Is 275/30R21 a safe plus-size upgrade from 265/35R21?: A plus-size upgrade is considered safe when overall diameter stays within ±3% — here the difference is 2.9%. This swap is within the typical safe range; speedometer and ABS calibration should remain close to factory.