1st= width, 3rd=diameter, 2nd= ???

[gtogtogto]

Im talking about the numbers on the side of a tire.
EX: 245/40/17
245 = width
17= diameter for rim
What does the 40 mean?

I believe my tires now are 245/40/17 and the tires I am looking at are only offered in 245/45/17 would the 40 and 45 difference cause a problem?
Thx

[traumadog]

2nd = aspect ratio.

That's the percentage of the width of the tire as the height of the sidewall.

So a 245/40 tire would have a 98mm sidewall, vs a 245/45 tire would have a 110.25 mm sidewall.

Said another way, the 245/40 tire would have a diameter of 24.5 mm (12.25mm * 2, or close to 1") smaller than the 245/45 tire.

Where it would matter is the speedometer/odometer readings; given these tire sizes (and the GTO's stock is 245/45/17), then your speedometer would be off by about 3.8-3.9%.

[gtogtogto]

Thank you