275-40-17's sidewall flex
 

I run 275 40 17 RA-1's for my track days and feel like there is too much side wall flex. Does anyone think that moving down to 255 width will loose much if any grip? It is .7" shorter in diameter.
If there is less sidewall will there be a better contact patch? I've yet to test with a pyrometer so I'm not sure what kind of contact patch I'm getting with the 275's. The better gearing from the smaller diameter couldn't hurt either (it will be kind of like the 3.9 final drive :) )

thoughts?

pressures
 

I run the same size not ra-1 but firehawks and I start out at about 35/36 psi cold and end up about 40/42. I don't sense flexing except when cold but that quickly changes.

Dave- Are you running 275's all the way around or are you just referring to the rears?

All around.

on what width rims? I run 17x9s, and when I switched from 255s to 275s, I noticed a huge grip improvement for autocross (Kuhmo Victorracers). On the racetrack though, not as noticeable.

Seriously you need 45 psi minimum in the RA-1's, at least I do.

Like 2003z said, I think it depends a lot on the wheel size. If you're running them on a stock 17" wheel, I doubt going to a 255 will result in much less grip, if any. The way the 275s bulge on that small of a rim, I doubt it will change much. If you're running say a 9" wheel, where a 275 is almost square, you might lose some going to a 255. I wouldn't lose any sleep over it, but if the car will feel better with a shorter sidewall, it might be worth it for that reason alone.

One thing to consider is tire wear. Supposedly the 275s wear a lot better than a smaller tire. While there isn't a huge difference between a 255 and 275 (in some cases), if the tire wear goes up, it's the battle of cost vs. performance. I autocrossed on 245s and a set of fronts lasted about 5 events, even with flipping them. And that's autocrossing!

I'm using 17 X 9.5's all around. I guess I'm just used to my old car with 235 40 17's with ultra low profile. I'm proably not loosing much if any grip, just don't have the turn in response I thought I would get. I'll have to have someone take my picture mid corner to see what it looks like under load.

The RA-1 is not the stiffest tire either... I ran a 255/40/17 Bridgestone RE540S which felt much stiffer (better turn in) than the 245/40/18 RA-1. I felt like the 255/40/17 is too short though.. especially with the 3.9fd.

The Yokohama A032 is known to be a pretty stiff tire as well... but in a car as heavy as the Z33 almost everything feels soft:o

Hey Jason weren't you running 255 RA-1's at t-hill last week? I'll have to go for a spin.

Yea- But I'm currently running a staggered set up- 255/40/17 in front and 275/40/17 in rear. The next track event will probably be ClubZ 2 day event in Jan. You're more than welcome to take my car for a couple of laps.

Carter Thompson, who placed 6ths at nationals last year (behind all the S2Ks), runs Hoosiers (275s on 17" sized wheels (7.5" front, 8" rear). He never said a single word about sidewall flex that I ever saw.

I think the hoosier side wall is much stiffer than the RA-1.
I actually think it is tread squirm that I am feeling (got them full tread for the winter rainy season). Now that I've got a couple events on them they are feeling much better. I forgot how much tread squirm is on the toyos when you get them unshaved.