chomp

I have a '92 Camaro RS, and I used to have the stock 8x16" wheels with 245/50 Futura GTX tires.


I recently put on 17x8.5" Z06 wheels and 255/40 Hankook Ventus HRII tires. I decided to go with 255 because the new wheels are wider, and I wanted better traction.

I realized that my only 245 tires are actually wider than the 255s! Now I know the second number (40..35..50.. or whatever) is a percentage of the first number, but why would my 255's be narrower than my 245s? I thought that was a fixed number for the tread width, in MM.

My friend got some 255's for his truck (made by Continental) and they are at least a good inch wider than my 255's. Did I get ripped off, or is there just something I don't know about tire specifications?

Apeiron

That's not tread width, it's section width. Width at the widest part of the tire.

chomp

Does that mean width from the outermost point of one side wall to the opposite side wall? It seems like that's the part of the tire that sticks out the furthest.


If so, there is no way these tires are 255's. The only thing i can think of is if the 255 measurement is really the length between the innermost points of the tire.. like where the insizde of the tire seals with the wheel. But then again, 255=about 10" and I don't think that part is that wide..

JeffW

http://www.tirerack.com/tires/tiretech/general/size.jsp


this may help

chomp

On the site where I bought the tires, it says that 255 is the tread width. The guy the first posted said it was the section width. In any case, my tires seem to be a lot smaller than they should be (especially if they are going by tread width).


Maybe this will clear things up: Do manufacturers vary the overall width of the tire, or is 255 supposed to be 255, regardless?


My friends 255's are a good 1-2" wider than mine (section width).

TheGreatJ

Apeiron is right, section width is total width at the widest point in millimeters. Aspect ratio (the second number i.e. 30, 40, 50) is sidewall height expressed as a percentage of section width. Last number is wheel size in inches. The reason they use mm for the section width and inches for the wheel size has always eluded me.

The thing you have to keep in mind, is that they didn't mount the tire on your wheels when they made the measurements at the factory. If the tire is designed for a 17x8" wheel and you mount it on a 17x8.5" it's going to change the tire profile and therefore change the sizes slightly.

chomp

Okay I understand the section, tread, and overall width now.

However, just by looking at the tires, mounted or unmounted, I can easily see at least a 3/4" difference between my 255's and 245's with the 245's being WIDER.


Like I said earlier, the Continental 255's look about 1.5" wider than my hankooks when they're unmounted. Is this just a manufacturer difference, because I feel cheated..

chomp

Here's some pictures I just took to help show what I'm talking about. On the left are the Futura 245/50's and on the right are my new Hankook 255/40's.

ME Leigh

The first number is suppoed to be section width, not tread width. But they really don't mean anything at all. All the size means is that all tires of the same size are close in size to each other. If you lookup different tires and different manufactors with the same size the tread width will vary dramatically. Its all how the manufactor sizes and rates their tires. You have to look at the specs more closely to find out if thats the size you want in that tire.

Here are some tires all 255/45/17 look how big of a difference there is in section width and tread with just between these 3.

Dunlop SP Sport 9000 94Y SL
255/40-17
10.4" section width
9.1" tread

Dunlop SP Sport 9000 SL
255/45-17
10" section width
9.1" tread width

GoodYear F1 GS-D3
255/45-17
98Y SL
9.9" section width
7.9" tread width

87350IROC

iTrader: (2)

That is very interesting, did you take those measurements yourself? My 245/50/16 Goodyear GS-D3s are 9.9"section and 9.0" tread width. Weird.

ME Leigh

No, those are manufacturers specs off of www.tirerack.com


Heres another
BFG g-force T/A KDW
255/45-17 98Y SL

Section width 10"
Tread width 8.2"

So it varies alot, I think thought that tires of the same size, have the same diameter, which is what really matters. Because all the tires i listed all have the same diam. 26.1"