Question 1

Which tire is taller, 155/55 R16 or 185/55 R15?

Accepted Answer

185/55 R15 is taller by 7.6 mm (1.32%) compared with 155/55 R16.

Question 2

What is the diameter difference between 155/55 R16 and 185/55 R15?

Accepted Answer

155/55 R16 measures 577 mm overall diameter, 185/55 R15 measures 585 mm — a difference of 7.6 mm (1.32%).

Question 3

How much speedometer error does this change create?

Accepted Answer

Switching from 155/55 R16 to 185/55 R15 changes the speedometer reading by +1.32%. At an indicated 100 km/h, your true speed becomes about 101.3 km/h.

Question 4

Is 185/55 R15 a safe replacement for 155/55 R16?

Accepted Answer

Within ±3% diameter — generally considered a safe replacement from a speedometer-error standpoint, provided wheel offset, rim width and clearance also match your vehicle.

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	155/55 R16	185/55 R15	Difference
Overall diameter	576.9 mm	584.5 mm	+7.6 mm (+1.32%)
Sidewall height	85.3 mm	101.8 mm	+16.5 mm
Circumference	1.812 m	1.836 m	+23.9 mm
Revs / km	551.8	544.6	-7.2
Ground clearance	reference	+3.8 mm	+3.8 mm
Speedometer @ 100 km/h	100.0 km/h	101.3 km/h	+1.32 km/h

155/55 R16 vs 185/55 R15

Detailed comparison

Verdict: excellent

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