What is the diameter difference between 205/55R16 and 225/45R18?

205/55R16 has an overall diameter of 24.88 inches (632 mm). 225/45R18 is 25.97 inches (660 mm). That's a 1.09 inch (28 mm) difference — 225/45R18 is taller.

Will 225/45R18 cause speedometer error on a car fitted with 205/55R16?

Swapping 205/55R16 for 225/45R18 produces a speedometer error of about 4.4%. Your speedometer will read lower than your actual speed — a 60 mph indicated reading is really 62.6 mph. Anything under 3% is usually acceptable without recalibration.

How many revolutions per mile does each size do?

205/55R16 turns 811 revs per mile. 225/45R18 turns 777 revs per mile. Taller tyres turn fewer times per mile, which lowers effective final-drive ratio.

What's the sidewall height difference?

205/55R16 has a sidewall of 113 mm (4.44 in). 225/45R18 sidewall is 101 mm (3.99 in). Lower-profile sidewalls give sharper steering response but less bump compliance.

Is 225/45R18 a safe plus-size upgrade from 205/55R16?

A plus-size upgrade is considered safe when overall diameter stays within ±3% — here the difference is 4.4%. This swap is outside the typical ±3% safe range and may require speedometer recalibration or affect ABS / traction control behaviour.

Tire size comparison

205/55R16 vs 225/45R18

Overall diameter, sidewall, revs per mile, and speedometer error — 225/45R18 is the taller tire, with a 4.4% speedo delta when swapping.

205/55R16

24.88in

632 mm overall diameter

225/45R18

25.97in

660 mm overall diameter

Diameter Δ

1.09 in

Speedo error

4.4%

205/55R16 revs/mi

811

225/45R18 revs/mi

777

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	205/55R16	225/45R18
Section width	205 mm	225 mm
Aspect ratio	55	45
Wheel diameter	16″	18″
Sidewall height	113 mm	101 mm
Overall diameter	24.88 in (632 mm)	25.97 in (660 mm)
Circumference	78.16 in	81.59 in
Revolutions / mile	811	777

Other comparisons for these sizes

185/65R14 vs 205/55R16 195/60R15 vs 205/55R16 205/55R16 vs 215/50R17 205/55R16 vs 205/50R17 205/55R16 vs 205/60R16 215/50R17 vs 225/45R18 225/50R17 vs 225/45R18 225/40R18 vs 225/45R18 225/45R18 vs 225/40R19 225/45R18 vs 245/35R20

FAQ

Frequently asked

What is the diameter difference between 205/55R16 and 225/45R18?: 205/55R16 has an overall diameter of 24.88 inches (632 mm). 225/45R18 is 25.97 inches (660 mm). That's a 1.09 inch (28 mm) difference — 225/45R18 is taller.
Will 225/45R18 cause speedometer error on a car fitted with 205/55R16?: Swapping 205/55R16 for 225/45R18 produces a speedometer error of about 4.4%. Your speedometer will read lower than your actual speed — a 60 mph indicated reading is really 62.6 mph. Anything under 3% is usually acceptable without recalibration.
How many revolutions per mile does each size do?: 205/55R16 turns 811 revs per mile. 225/45R18 turns 777 revs per mile. Taller tyres turn fewer times per mile, which lowers effective final-drive ratio.
What's the sidewall height difference?: 205/55R16 has a sidewall of 113 mm (4.44 in). 225/45R18 sidewall is 101 mm (3.99 in). Lower-profile sidewalls give sharper steering response but less bump compliance.
Is 225/45R18 a safe plus-size upgrade from 205/55R16?: A plus-size upgrade is considered safe when overall diameter stays within ±3% — here the difference is 4.4%. This swap is outside the typical ±3% safe range and may require speedometer recalibration or affect ABS / traction control behaviour.