Question 1

Which tire is taller, 325/55 R16 or 255/50 R20?

Accepted Answer

325/55 R16 is taller by 0.9 mm (0.12%) compared with 255/50 R20.

Question 2

What is the diameter difference between 325/55 R16 and 255/50 R20?

Accepted Answer

325/55 R16 measures 764 mm overall diameter, 255/50 R20 measures 763 mm — a difference of 0.9 mm (0.12%).

Question 3

How much speedometer error does this change create?

Accepted Answer

Switching from 325/55 R16 to 255/50 R20 changes the speedometer reading by -0.12%. At an indicated 100 km/h, your true speed becomes about 99.9 km/h.

Question 4

Is 255/50 R20 a safe replacement for 325/55 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	325/55 R16	255/50 R20	Difference
Overall diameter	763.9 mm	763.0 mm	-0.9 mm (-0.12%)
Sidewall height	178.8 mm	127.5 mm	-51.3 mm
Circumference	2.400 m	2.397 m	-2.8 mm
Revs / km	416.7	417.2	+0.5
Ground clearance	reference	-0.4 mm	-0.4 mm
Speedometer @ 100 km/h	100.0 km/h	99.9 km/h	-0.12 km/h

325/55 R16 vs 255/50 R20

Detailed comparison

Verdict: excellent

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