I bought a used set of 315's to slap on my chrome ZR1 rims... and I guess time took it's toll. At ~20psi we saw som cracks forming on the shoulder, so the 315 set was a wash. Just as well, the used set had some rubbing on the other shoulder due to it's being run on a Z28 (narrower wheel well lips).

As a substitute for now, I had some new 275/40ZR17 Eagle F1's I had laying around put on the front rims, and the 285/40ZR17 Eagle GSC's that were up front (on the 17x9.5" rims) are now mounted on the 17x11" rims out back.

1) Yes, they look "stretched" a bit out... but mean.

2) Yes, they handle GREAT...

hate to say it, but Porsche may be onto something with their wheel/tire choices. I think 295's would look a bit better, but then again, the 315's that I had mounted looked killer as well. The 285's are a bit too much of a stretch for me, but they do feel great.

I'll run the 285's for a while, and once I get my spare pair of 17"x9.5" ZR1 rims chromed (and 275 Eagle F1's mounted), I'll be looking for some proper 315's... read my other post for the brand/model... you may be suprised.

 

Can ya post any pics of the 285's on the 17X11 wheel. Curious to see how the look.

 

I'll see if I can post some in a few days. She look's great, but they do look a bit stretched out.

305's would probably look fine, the 315's looked great (when I had them mounted), but I wouldn't go any bigger.

The Michelin Pilot Sport's come in 315 and also 335/35YR17. The section width would be ~13.0" on an 11" rim (the tire is rated for use on rims 11" to 12") ... but the 315 is 12.6" on an 11" rim... not much gain in section width, and much less sidewall stability with the 335. Although you do get a 26" tire, instead of the stock 25.6" giving you about 1.5% less gear ratio. (no big deal.. you [i]almost[/] go from 4.11's to 4.10's )

The Dunlop SP Sport 8000 has a similar 315 or 335 option. The 335 is rated for more load, and has a larger diameter (26.1", again about 1.5% gear loss) but the section width is listed as only 12.4", smaller than the Michelin Pilot sports' 315! Go figure.

Perrilli PZero Asymetrical tires are available in 335/35ZR17 aswell... however the section width is a huge 13.4"! I doubt that would fit even a Pontiac wheel well without some fender lip rolling. Diameter starts to climb a bit as well with 26.2"

Last one worth noting is the Kuhmo Ecsta V700. They come in 275's and 335's... nothing inbetween (wierd), but the 335 is 13.1" section width (on 11" rim), while the diameter is 26". Probably a good tire to look at for DOT-legal racing, but the treadwear (like most competition-only tires) is fairly limited... treadwear: 50. I bet it holds like glue though!

Personally I'm waiting for the 315 Nitto 555R-II which should be out by 3rd quarter...

* If you want a big number on your sidewall, go with the Dunlop 335's, otherwise I'd imagine the "massaging" would have to be fairly significant.

* For best grip I'd stick with a 315, but compound would probably have more to do with this than the stated section width or tread width. (as you can see above, we're talking about marginal differences between sizes and brands, I'd wager that contact patch area actually varries less that that as well).

* For best horizontal transistions, I'd probably stay to a 305 if possible, but again, compound and sidewall stiffness is probably more important than how "stretched" the tire is. I'm set against anything beyond 315 though... if I need more tire, I'll be buying 17x12" or 18x12" rims instead.

I know it sounds vague overall since the Make and Models seem to determine the tire qualities more than the size does, but for Goodyear GSC's I can tell you that:
a) 285's physically fit on 11" wide rims

b) they are very responsive in lane changes and other horizontal transitions

c) they felt MUCH softer/spongy (laterally) when mounted on my front 17"x9.5" rims... personally, if I was in charge of Goodyear, I'd have no problems re-labeling these as 295's and moving the smallest recomended rim width up from 9.5 to 10". They felt a bit too squishy on 9.5" widths for my taste (although they did bite real nice when braking hard). The Goodyear F1 275's that replaced them up front seem to do much better, although I'm not sure if it's totally due to the slightly smaller tread, or the fact that they are F1's (although the F1's are rated 300 tread wear, while the GSC's are only 220, so you'd assume they're harder rubber and would transition better I dunno).

d) they are cheaper than 315's

 

Steve did you ever take any pics? I'm curious to see the results before doing it myself. Thanks.

 

This is a case where there's a discrepancy between conventional appearance and some measure of actual performance (transitions, in this case). Consider that the perception of appearance is tied to what you see on an everyday basis - pretty much OE or similar combinations, which tend to be on the narrow end of the rim width:tire width range. If you really want that extra performance, knowing that it's there should eventually be enough to shift your opinion of the appearance. The only downsides appear to be some difficulty in getting the beads to seat and a rather less than soft ride.

You've actually stiffened the support for the tread both laterally (force) and in terms of moment about the steering axis (which relates the slip angle at the contact patch to how much further you have to steer the wheel than the math using overall steering ratio predicts to get it there). The increased stiffness means that the natural frequency has gone up, which you read as "more linear".

Most (if not all) 275/40 tires carry the manufacturer's approval for mounting on 11" rims, and you can probably fudge that by another half inch or so (though you might have some difficulty getting any warranty honored). A 285 is nearly half an inch wider yet, so I'd guess that a reasonable safe upper limit on rim width that you can physically stretch a 285 onto is at least 12". Remember that each half inch of rim width beyond the width of the rim on which the tire's nominal measurements were made increases the section width by about 0.2" (5 mm) and the unloaded section height decreases by 0.025". Another rough guide for maximum rim width is an inch to an inch and a half bigger than the measured tread width (this is somewhat dependent on the sidewall height).

There's a tolerance on all tire dimensions. While I'm not sure what it is, I've heard the figure 7%, though that figure was without reference as to whether it was +7%/-7%, a 7% total range width, or something else. Anyway, that should help explain the different section width measurements.

By now, you might have guessed where my tire & rim combinations tend to end up - at or 1/2" beyond the maximum widths generally listed for a given tire size.

Norm

 

Norm,

I ran 275 Kumho Victoracers on my 11" wheels for a short time for the same as Steve. I already had the tires when I got the wheels. They worked well and looked awesome. When I laid the tires on top of each other the rubber of the tires never contacted each other. The rim "bead" stuck out further than the tire by a good bit.

However, when I finally put some Kumho 315 tires on there the handling difference was phenomenal! Our F bodies should have come with this tire/wheel combo from the factory.