I see people saying that a 205 section width tire is roughly 8 inches so an 8 inch rim is the correct size rim. I have some loose 205 50 15 AD08's. Ok they may measure roughly 8 inches across the tread face but from outside of the bead to outside of the bead they measure 6 inches. So it would seem that using a 7 or 7.5 inch rim already stretches the tire quite a bit.

 

205s mounted on a 6.5" rim are rated 7.5" wide that usually contacts the road and the entire thread is about 8.5" however that extra inch is rounded up so overall thats 1" extra width that you get by stretching the tire.

 

Tread width > wheel width

Measuring the distance between the beads on an unseated tire is probably the most useless measurement you could take on a tire. That distance will change based on nothing but the weather.

 

if we talk about it, we legitimize it.

 

Valid point but is there a design reason why the bead width is narrower than the tread width? They could design tires with bead width as wide as the tread. (other than protecting the rim lip by recessing it)

 

So then how are you supposed to estimate if your wheels and prospective tires will work together if you dont have them in hand??????

 

Read dimensions online.

 

and add .5-1 inch to the max suggested wheel width.

 

Would everyone else agree with this method? Better place to ask than club roadster, since they will put a 185 on a 15x9.

 

The manufacturers have a range of appropriate rim widths and I'm pretty sure that engineers figure that stuff out. Maybe they are conservative in their estimates and understate the range but I'm not so sure that running a smaller tire overstretched is the best idea. I understand that most guys here aren't going all clubroadster on their stretching but the track guys are putting more stress on the sidewalls than would occur under normal on road driving conditions.

 

Most 205's are suggested to max 7 or 7.5, 225 suggested max 8 or 8.5.
Still they are fastest on 8's and 9's, without blowing up in our faces.
Manufacturers have a lot of other things than performance to worry about (whining M.netters complaining about scuffed wheel rims etc).

There are of course exceptions where the suggested widths are just perfect, but that's normally not the case for high profile DOT tires.

 

In my experience, radials, will yield their best grip when mounted on a wheel that is equal to, or wider than the tread width. We have tested tires mounted on wheels about 1" wider than the tread and seen no real gains.

Examples of a few popular track wheel/tire combinations:

205 NT01 on 15x8
8.35" Casing measured on a 6.5" wheel(spec from Nitto website)

225/45 NT01 on 15x9 wheel
8.86" casing measured on a 7.5" wheel (spec from Nitto website)

205/50/15 Hoosier A6/R6 have somewhat cantilevered sidewalls
Spec from Hoosier website
8.7" casing measured on 6.5" wheel
8" tread width measured on same 6.5" wheel

The Hoosier 205/50/15, being closer to everyone else's 225/45 in size, is faster on a 9" wheel. The 225/45 Hoosier can be run on a 9 or a 10 and seems about the same either way.

To me, stretched is when the wheel is over 2" wider than the tread.

 

And yet most modern performance oriented cars come with slightly "stretched" tires. Also designed by Engineers. Seriously, there's too many cars to even list, that all come with a tire that is slightly stretched for the wheel. Bimmer M, Lexus IsF, all higher end subarus, etc etc etc.












You get the point.
I think the biggest thing is sticking to that .5-1 "rule" someone stated previously, as the OEM's all seem to be in that area based on everything I've seen.

 

I agree.

 

When I think stretched, I picture this:



And instantly think of clubretard.

Its not that hard to distinguish between "hard parker/retard/dor!fto" and " slight stretch"

 

God, that is so retarded. I can't understand how some people like that. It looks goofy as ----, and the car probably rides and drives like ----, and drags over every bump.

I prefer stretched tire, just not at that extreme. 185/195 on a 7" or 7.5", or a 205 on an 8" wheel is just right. Enough to tighten up the sidewalls, but not so much that it looks like that. 225 on a 9" is what I'd like, but I'm going smaller and lighter with a 195/60 on a 14x7 for cost reasons (extended cost from ruptured tires because of potholes and ---- roads).

 

What about an advantage of side wall stiffness? Wouldn't a stretched tire act like it's sidewalls were stiffer?

 

Nate you talking about the white ricer? Wider rims help sidewall stiffness but not THAT much. Too much negates the affect.

 

I was talking about the exotics that 18psi mentioned. Stretched like that cr car is by no means performance oriented.

 

slight stretch is okay. I'd rock 205 on a 9"