What is the diameter difference between 305/30R22 and 325/30R22?

305/30R22 has an overall diameter of 29.2 inches (742 mm). 325/30R22 is 29.68 inches (754 mm). That's a 0.47 inch (12 mm) difference — 325/30R22 is taller.

Will 325/30R22 cause speedometer error on a car fitted with 305/30R22?

Swapping 305/30R22 for 325/30R22 produces a speedometer error of about 1.6%. Your speedometer will read lower than your actual speed — a 60 mph indicated reading is really 61 mph. Anything under 3% is usually acceptable without recalibration.

How many revolutions per mile does each size do?

305/30R22 turns 691 revs per mile. 325/30R22 turns 680 revs per mile. Taller tyres turn fewer times per mile, which lowers effective final-drive ratio.

What's the sidewall height difference?

305/30R22 has a sidewall of 92 mm (3.6 in). 325/30R22 sidewall is 98 mm (3.84 in). Lower-profile sidewalls give sharper steering response but less bump compliance.

Is 325/30R22 a safe plus-size upgrade from 305/30R22?

A plus-size upgrade is considered safe when overall diameter stays within ±3% — here the difference is 1.6%. This swap is within the typical safe range; speedometer and ABS calibration should remain close to factory.

Tire size comparison

305/30R22 vs 325/30R22

Overall diameter, sidewall, revs per mile, and speedometer error — 325/30R22 is the taller tire, with a 1.6% speedo delta when swapping.

305/30R22

29.2in

742 mm overall diameter

325/30R22

29.68in

754 mm overall diameter

Diameter Δ

0.47 in

Speedo error

1.6%

305/30R22 revs/mi

691

325/30R22 revs/mi

680

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	305/30R22	325/30R22
Section width	305 mm	325 mm
Aspect ratio	30	30
Wheel diameter	22″	22″
Sidewall height	92 mm	98 mm
Overall diameter	29.2 in (742 mm)	29.68 in (754 mm)
Circumference	91.75 in	93.23 in
Revolutions / mile	691	680

Other comparisons for these sizes

295/35R21 vs 305/30R22 285/30R22 vs 305/30R22 295/30R22 vs 305/30R22 295/35R22 vs 305/30R22 305/30R22 vs 315/30R22 315/30R22 vs 325/30R22

FAQ

Frequently asked

What is the diameter difference between 305/30R22 and 325/30R22?: 305/30R22 has an overall diameter of 29.2 inches (742 mm). 325/30R22 is 29.68 inches (754 mm). That's a 0.47 inch (12 mm) difference — 325/30R22 is taller.
Will 325/30R22 cause speedometer error on a car fitted with 305/30R22?: Swapping 305/30R22 for 325/30R22 produces a speedometer error of about 1.6%. Your speedometer will read lower than your actual speed — a 60 mph indicated reading is really 61 mph. Anything under 3% is usually acceptable without recalibration.
How many revolutions per mile does each size do?: 305/30R22 turns 691 revs per mile. 325/30R22 turns 680 revs per mile. Taller tyres turn fewer times per mile, which lowers effective final-drive ratio.
What's the sidewall height difference?: 305/30R22 has a sidewall of 92 mm (3.6 in). 325/30R22 sidewall is 98 mm (3.84 in). Lower-profile sidewalls give sharper steering response but less bump compliance.
Is 325/30R22 a safe plus-size upgrade from 305/30R22?: A plus-size upgrade is considered safe when overall diameter stays within ±3% — here the difference is 1.6%. This swap is within the typical safe range; speedometer and ABS calibration should remain close to factory.