Question 1

Which tire is taller, 175/65 R15 or 205/40 R17?

Accepted Answer

175/65 R15 is taller by 12.7 mm (2.09%) compared with 205/40 R17.

Question 2

What is the diameter difference between 175/65 R15 and 205/40 R17?

Accepted Answer

175/65 R15 measures 609 mm overall diameter, 205/40 R17 measures 596 mm — a difference of 12.7 mm (2.09%).

Question 3

How much speedometer error does this change create?

Accepted Answer

Switching from 175/65 R15 to 205/40 R17 changes the speedometer reading by -2.09%. At an indicated 100 km/h, your true speed becomes about 97.9 km/h.

Question 4

Is 205/40 R17 a safe replacement for 175/65 R15?

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	175/65 R15	205/40 R17	Difference
Overall diameter	608.5 mm	595.8 mm	-12.7 mm (-2.09%)
Sidewall height	113.8 mm	82.0 mm	-31.8 mm
Circumference	1.912 m	1.872 m	-39.9 mm
Revs / km	523.1	534.3	+11.2
Ground clearance	reference	-6.4 mm	-6.4 mm
Speedometer @ 100 km/h	100.0 km/h	97.9 km/h	-2.09 km/h

175/65 R15 vs 205/40 R17

Detailed comparison

Verdict: excellent

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