Question 1

Which tire is taller, 155/55 R16 or 245/40 R17?

Accepted Answer

245/40 R17 is taller by 50.9 mm (8.82%) compared with 155/55 R16.

Question 2

What is the diameter difference between 155/55 R16 and 245/40 R17?

Accepted Answer

155/55 R16 measures 577 mm overall diameter, 245/40 R17 measures 628 mm — a difference of 50.9 mm (8.82%).

Question 3

How much speedometer error does this change create?

Accepted Answer

Switching from 155/55 R16 to 245/40 R17 changes the speedometer reading by +8.82%. At an indicated 100 km/h, your true speed becomes about 108.8 km/h.

Question 4

Is 245/40 R17 a safe replacement for 155/55 R16?

Accepted Answer

Over 5% diameter difference. This is outside the common safe range and can affect speedometer accuracy, ABS calibration and gearing. Not recommended without professional review.

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	245/40 R17	Difference
Overall diameter	576.9 mm	627.8 mm	+50.9 mm (+8.82%)
Sidewall height	85.3 mm	98.0 mm	+12.8 mm
Circumference	1.812 m	1.972 m	+159.9 mm
Revs / km	551.8	507.0	-44.7
Ground clearance	reference	+25.4 mm	+25.4 mm
Speedometer @ 100 km/h	100.0 km/h	108.8 km/h	+8.82 km/h

155/55 R16 vs 245/40 R17

Detailed comparison

Verdict: danger

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