What is the diameter difference between 285/30R21 and 295/30R21?

285/30R21 has an overall diameter of 27.73 inches (704 mm). 295/30R21 is 27.97 inches (710 mm). That's a 0.24 inch (6 mm) difference — 295/30R21 is taller.

Will 295/30R21 cause speedometer error on a car fitted with 285/30R21?

Swapping 285/30R21 for 295/30R21 produces a speedometer error of about 0.9%. Your speedometer will read lower than your actual speed — a 60 mph indicated reading is really 60.5 mph. Anything under 3% is usually acceptable without recalibration.

How many revolutions per mile does each size do?

285/30R21 turns 727 revs per mile. 295/30R21 turns 721 revs per mile. Taller tyres turn fewer times per mile, which lowers effective final-drive ratio.

What's the sidewall height difference?

285/30R21 has a sidewall of 86 mm (3.37 in). 295/30R21 sidewall is 89 mm (3.48 in). Lower-profile sidewalls give sharper steering response but less bump compliance.

Is 295/30R21 a safe plus-size upgrade from 285/30R21?

A plus-size upgrade is considered safe when overall diameter stays within ±3% — here the difference is 0.9%. This swap is within the typical safe range; speedometer and ABS calibration should remain close to factory.

Tire size comparison

285/30R21 vs 295/30R21

Overall diameter, sidewall, revs per mile, and speedometer error — 295/30R21 is the taller tire, with a 0.9% speedo delta when swapping.

285/30R21

27.73in

704 mm overall diameter

295/30R21

27.97in

710 mm overall diameter

Diameter Δ

0.24 in

Speedo error

0.9%

285/30R21 revs/mi

727

295/30R21 revs/mi

721

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	285/30R21	295/30R21
Section width	285 mm	295 mm
Aspect ratio	30	30
Wheel diameter	21″	21″
Sidewall height	86 mm	89 mm
Overall diameter	27.73 in (704 mm)	27.97 in (710 mm)
Circumference	87.12 in	87.87 in
Revolutions / mile	727	721

Other comparisons for these sizes

275/35R20 vs 285/30R21 285/35R20 vs 295/30R21 285/35R20 vs 285/30R21 295/35R20 vs 295/30R21 275/30R21 vs 285/30R21 275/30R21 vs 295/30R21 275/35R21 vs 285/30R21 285/30R21 vs 305/30R21 295/30R21 vs 305/30R21 295/30R21 vs 315/30R21

FAQ

Frequently asked

What is the diameter difference between 285/30R21 and 295/30R21?: 285/30R21 has an overall diameter of 27.73 inches (704 mm). 295/30R21 is 27.97 inches (710 mm). That's a 0.24 inch (6 mm) difference — 295/30R21 is taller.
Will 295/30R21 cause speedometer error on a car fitted with 285/30R21?: Swapping 285/30R21 for 295/30R21 produces a speedometer error of about 0.9%. Your speedometer will read lower than your actual speed — a 60 mph indicated reading is really 60.5 mph. Anything under 3% is usually acceptable without recalibration.
How many revolutions per mile does each size do?: 285/30R21 turns 727 revs per mile. 295/30R21 turns 721 revs per mile. Taller tyres turn fewer times per mile, which lowers effective final-drive ratio.
What's the sidewall height difference?: 285/30R21 has a sidewall of 86 mm (3.37 in). 295/30R21 sidewall is 89 mm (3.48 in). Lower-profile sidewalls give sharper steering response but less bump compliance.
Is 295/30R21 a safe plus-size upgrade from 285/30R21?: A plus-size upgrade is considered safe when overall diameter stays within ±3% — here the difference is 0.9%. This swap is within the typical safe range; speedometer and ABS calibration should remain close to factory.