Question 1

Which tire is taller, 185/65 R15 or 245/40 R17?

Accepted Answer

245/40 R17 is taller by 6.3 mm (1.01%) compared with 185/65 R15.

Question 2

What is the diameter difference between 185/65 R15 and 245/40 R17?

Accepted Answer

185/65 R15 measures 622 mm overall diameter, 245/40 R17 measures 628 mm — a difference of 6.3 mm (1.01%).

Question 3

How much speedometer error does this change create?

Accepted Answer

Switching from 185/65 R15 to 245/40 R17 changes the speedometer reading by +1.01%. At an indicated 100 km/h, your true speed becomes about 101.0 km/h.

Question 4

Is 245/40 R17 a safe replacement for 185/65 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	185/65 R15	245/40 R17	Difference
Overall diameter	621.5 mm	627.8 mm	+6.3 mm (+1.01%)
Sidewall height	120.3 mm	98.0 mm	-22.3 mm
Circumference	1.952 m	1.972 m	+19.8 mm
Revs / km	512.2	507.0	-5.1
Ground clearance	reference	+3.1 mm	+3.1 mm
Speedometer @ 100 km/h	100.0 km/h	101.0 km/h	+1.01 km/h

185/65 R15 vs 245/40 R17

Detailed comparison

Verdict: excellent

Related comparisons

Frequently asked questions