Question 1

Which tire is taller, 255/45 R18 or 225/40 R19?

Accepted Answer

255/45 R18 is taller by 24.1 mm (3.51%) compared with 225/40 R19.

Question 2

What is the diameter difference between 255/45 R18 and 225/40 R19?

Accepted Answer

255/45 R18 measures 687 mm overall diameter, 225/40 R19 measures 663 mm — a difference of 24.1 mm (3.51%).

Question 3

How much speedometer error does this change create?

Accepted Answer

Switching from 255/45 R18 to 225/40 R19 changes the speedometer reading by -3.51%. At an indicated 100 km/h, your true speed becomes about 96.5 km/h.

Question 4

Is 225/40 R19 a safe replacement for 255/45 R18?

Accepted Answer

Between 3% and 5% diameter difference — speedometer drift is noticeable. Consider recalibration and confirm clearance with your vehicle's manufacturer specification.

Question 5

What else should I check before changing tire size?

Accepted Answer

Beyond diameter and speedometer error, verify wheel offset (ET), rim width, hub bore, load index, brake and suspension clearance, and your vehicle's manufacturer specification. Local regulations may also limit how far you can deviate from OEM.

Metric	255/45 R18	225/40 R19	Difference
Overall diameter	686.7 mm	662.6 mm	-24.1 mm (-3.51%)
Sidewall height	114.8 mm	90.0 mm	-24.8 mm
Circumference	2.157 m	2.082 m	-75.7 mm
Revs / km	463.5	480.4	+16.9
Ground clearance	reference	-12.1 mm	-12.1 mm
Speedometer @ 100 km/h	100.0 km/h	96.5 km/h	-3.51 km/h

255/45 R18 vs 225/40 R19

Detailed comparison

Verdict: warning

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