What is the diameter difference between 275/35R18 and 275/30R19?

275/35R18 has an overall diameter of 25.58 inches (650 mm). 275/30R19 is 25.5 inches (648 mm). That's a 0.08 inch (2 mm) difference — 275/30R19 is shorter.

Will 275/30R19 cause speedometer error on a car fitted with 275/35R18?

Swapping 275/35R18 for 275/30R19 produces a speedometer error of about 0.3%. Your speedometer will read higher than your actual speed — a 60 mph indicated reading is really 59.8 mph. Anything under 3% is usually acceptable without recalibration.

How many revolutions per mile does each size do?

275/35R18 turns 788 revs per mile. 275/30R19 turns 791 revs per mile. Taller tyres turn fewer times per mile, which lowers effective final-drive ratio.

What's the sidewall height difference?

275/35R18 has a sidewall of 96 mm (3.79 in). 275/30R19 sidewall is 83 mm (3.25 in). Lower-profile sidewalls give sharper steering response but less bump compliance.

Is 275/30R19 a safe plus-size upgrade from 275/35R18?

A plus-size upgrade is considered safe when overall diameter stays within ±3% — here the difference is 0.3%. This swap is within the typical safe range; speedometer and ABS calibration should remain close to factory.

Tire size comparison

275/35R18 vs 275/30R19

Overall diameter, sidewall, revs per mile, and speedometer error — 275/35R18 is the taller tire, with a 0.3% speedo delta when swapping.

275/35R18

25.58in

650 mm overall diameter

275/30R19

25.5in

648 mm overall diameter

Diameter Δ

0.08 in

Speedo error

0.3%

275/35R18 revs/mi

788

275/30R19 revs/mi

791

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	275/35R18	275/30R19
Section width	275 mm	275 mm
Aspect ratio	35	30
Wheel diameter	18″	19″
Sidewall height	96 mm	83 mm
Overall diameter	25.58 in (650 mm)	25.5 in (648 mm)
Circumference	80.36 in	80.1 in
Revolutions / mile	788	791

Other comparisons for these sizes

255/35R18 vs 275/35R18 265/35R18 vs 275/30R19 265/35R18 vs 275/35R18 275/35R18 vs 285/30R19 275/35R18 vs 275/40R18 265/30R19 vs 275/30R19 265/35R19 vs 275/30R19 275/30R19 vs 285/30R19 275/30R19 vs 275/35R19

FAQ

Frequently asked

What is the diameter difference between 275/35R18 and 275/30R19?: 275/35R18 has an overall diameter of 25.58 inches (650 mm). 275/30R19 is 25.5 inches (648 mm). That's a 0.08 inch (2 mm) difference — 275/30R19 is shorter.
Will 275/30R19 cause speedometer error on a car fitted with 275/35R18?: Swapping 275/35R18 for 275/30R19 produces a speedometer error of about 0.3%. Your speedometer will read higher than your actual speed — a 60 mph indicated reading is really 59.8 mph. Anything under 3% is usually acceptable without recalibration.
How many revolutions per mile does each size do?: 275/35R18 turns 788 revs per mile. 275/30R19 turns 791 revs per mile. Taller tyres turn fewer times per mile, which lowers effective final-drive ratio.
What's the sidewall height difference?: 275/35R18 has a sidewall of 96 mm (3.79 in). 275/30R19 sidewall is 83 mm (3.25 in). Lower-profile sidewalls give sharper steering response but less bump compliance.
Is 275/30R19 a safe plus-size upgrade from 275/35R18?: A plus-size upgrade is considered safe when overall diameter stays within ±3% — here the difference is 0.3%. This swap is within the typical safe range; speedometer and ABS calibration should remain close to factory.