What is the diameter difference between 295/30R21 and 295/35R21?

295/30R21 has an overall diameter of 27.97 inches (710 mm). 295/35R21 is 29.13 inches (740 mm). That's a 1.16 inch (30 mm) difference — 295/35R21 is taller.

Will 295/35R21 cause speedometer error on a car fitted with 295/30R21?

Swapping 295/30R21 for 295/35R21 produces a speedometer error of about 4.2%. Your speedometer will read lower than your actual speed — a 60 mph indicated reading is really 62.5 mph. Anything under 3% is usually acceptable without recalibration.

How many revolutions per mile does each size do?

295/30R21 turns 721 revs per mile. 295/35R21 turns 692 revs per mile. Taller tyres turn fewer times per mile, which lowers effective final-drive ratio.

What's the sidewall height difference?

295/30R21 has a sidewall of 89 mm (3.48 in). 295/35R21 sidewall is 103 mm (4.06 in). Lower-profile sidewalls give sharper steering response but less bump compliance.

Is 295/35R21 a safe plus-size upgrade from 295/30R21?

A plus-size upgrade is considered safe when overall diameter stays within ±3% — here the difference is 4.2%. This swap is outside the typical ±3% safe range and may require speedometer recalibration or affect ABS / traction control behaviour.

Tire size comparison

295/30R21 vs 295/35R21

Overall diameter, sidewall, revs per mile, and speedometer error — 295/35R21 is the taller tire, with a 4.2% speedo delta when swapping.

295/30R21

27.97in

710 mm overall diameter

295/35R21

29.13in

740 mm overall diameter

Diameter Δ

1.16 in

Speedo error

4.2%

295/30R21 revs/mi

721

295/35R21 revs/mi

692

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	295/30R21	295/35R21
Section width	295 mm	295 mm
Aspect ratio	30	35
Wheel diameter	21″	21″
Sidewall height	89 mm	103 mm
Overall diameter	27.97 in (710 mm)	29.13 in (740 mm)
Circumference	87.87 in	91.51 in
Revolutions / mile	721	692

Other comparisons for these sizes

285/35R20 vs 295/30R21 295/35R20 vs 295/30R21 275/30R21 vs 295/30R21 275/35R21 vs 295/35R21 285/30R21 vs 295/30R21 295/30R21 vs 305/30R21 295/30R21 vs 315/30R21 295/35R21 vs 305/30R22 295/35R21 vs 295/30R22 295/35R21 vs 305/30R21

FAQ

Frequently asked

What is the diameter difference between 295/30R21 and 295/35R21?: 295/30R21 has an overall diameter of 27.97 inches (710 mm). 295/35R21 is 29.13 inches (740 mm). That's a 1.16 inch (30 mm) difference — 295/35R21 is taller.
Will 295/35R21 cause speedometer error on a car fitted with 295/30R21?: Swapping 295/30R21 for 295/35R21 produces a speedometer error of about 4.2%. Your speedometer will read lower than your actual speed — a 60 mph indicated reading is really 62.5 mph. Anything under 3% is usually acceptable without recalibration.
How many revolutions per mile does each size do?: 295/30R21 turns 721 revs per mile. 295/35R21 turns 692 revs per mile. Taller tyres turn fewer times per mile, which lowers effective final-drive ratio.
What's the sidewall height difference?: 295/30R21 has a sidewall of 89 mm (3.48 in). 295/35R21 sidewall is 103 mm (4.06 in). Lower-profile sidewalls give sharper steering response but less bump compliance.
Is 295/35R21 a safe plus-size upgrade from 295/30R21?: A plus-size upgrade is considered safe when overall diameter stays within ±3% — here the difference is 4.2%. This swap is outside the typical ±3% safe range and may require speedometer recalibration or affect ABS / traction control behaviour.