What is the diameter difference between 235/40R18 and 235/35R19?

235/40R18 has an overall diameter of 25.4 inches (645 mm). 235/35R19 is 25.48 inches (647 mm). That's a 0.07 inch (2 mm) difference — 235/35R19 is taller.

Will 235/35R19 cause speedometer error on a car fitted with 235/40R18?

Swapping 235/40R18 for 235/35R19 produces a speedometer error of about 0.3%. Your speedometer will read lower than your actual speed — a 60 mph indicated reading is really 60.2 mph. Anything under 3% is usually acceptable without recalibration.

How many revolutions per mile does each size do?

235/40R18 turns 794 revs per mile. 235/35R19 turns 792 revs per mile. Taller tyres turn fewer times per mile, which lowers effective final-drive ratio.

What's the sidewall height difference?

235/40R18 has a sidewall of 94 mm (3.7 in). 235/35R19 sidewall is 82 mm (3.24 in). Lower-profile sidewalls give sharper steering response but less bump compliance.

Is 235/35R19 a safe plus-size upgrade from 235/40R18?

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

235/40R18 vs 235/35R19

Overall diameter, sidewall, revs per mile, and speedometer error — 235/35R19 is the taller tire, with a 0.3% speedo delta when swapping.

235/40R18

25.4in

645 mm overall diameter

235/35R19

25.48in

647 mm overall diameter

Diameter Δ

0.07 in

Speedo error

0.3%

235/40R18 revs/mi

794

235/35R19 revs/mi

792

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	235/40R18	235/35R19
Section width	235 mm	235 mm
Aspect ratio	40	35
Wheel diameter	18″	19″
Sidewall height	94 mm	82 mm
Overall diameter	25.4 in (645 mm)	25.48 in (647 mm)
Circumference	79.8 in	80.04 in
Revolutions / mile	794	792

Other comparisons for these sizes

225/45R17 vs 235/40R18 235/45R17 vs 235/40R18 215/40R18 vs 235/40R18 225/40R18 vs 235/35R19 225/40R18 vs 235/40R18 225/45R18 vs 235/40R18 235/40R18 vs 245/35R19 235/40R18 vs 255/30R20 235/40R18 vs 245/40R18 235/40R18 vs 255/40R18

FAQ

Frequently asked

What is the diameter difference between 235/40R18 and 235/35R19?: 235/40R18 has an overall diameter of 25.4 inches (645 mm). 235/35R19 is 25.48 inches (647 mm). That's a 0.07 inch (2 mm) difference — 235/35R19 is taller.
Will 235/35R19 cause speedometer error on a car fitted with 235/40R18?: Swapping 235/40R18 for 235/35R19 produces a speedometer error of about 0.3%. Your speedometer will read lower than your actual speed — a 60 mph indicated reading is really 60.2 mph. Anything under 3% is usually acceptable without recalibration.
How many revolutions per mile does each size do?: 235/40R18 turns 794 revs per mile. 235/35R19 turns 792 revs per mile. Taller tyres turn fewer times per mile, which lowers effective final-drive ratio.
What's the sidewall height difference?: 235/40R18 has a sidewall of 94 mm (3.7 in). 235/35R19 sidewall is 82 mm (3.24 in). Lower-profile sidewalls give sharper steering response but less bump compliance.
Is 235/35R19 a safe plus-size upgrade from 235/40R18?: 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.