if you are planning on going FI, ... i strongly recommend a wider tire than 275...

just my 2¢

 

A 275 works pretty well, but wider is better. On the Term. a 9.5 in rim would fit a 275 well, and a 10.5 would fit a 315 well. I read some of the posts about using a 285 on a 315 ?? That seems like it will have that "barely holding onto the rim" look. Anything over those sizes seemed to look bubbled, and under look like the tire was stretching to fit on there. Either way at high speeds 100+, that is a bad thing. Fitting flush is the best way to go.

 

No they don't work pretty well with FI. I've been running 285s and I still couldn't get traction through 3rd.

 

yes, it does depend on the rim size, and it will also depend upon the Brand tire as to how it will look/perform mounted. If you look at the Specs of whatever tire brand you're looking at (on tirerack for instance), you can see the manufacturers recommended rim widths, as long as you stay within those recommendations, you will be fine.

I would recommend, since you are going FI, to get at least a 10" wide rear rim, and 285+ rear tire. You can easily fit a 305 back there with 285 up front.
I am currently trying to figure out which tires to go with as well.....

 

You need better/softer tires. I had 485tq on the Cobra and they hooked just fine till about 40% left.

 

Will I need larger than the 275's, even if I am running only 7-8 lbs of boost and 370 rwhp?

The tires I want are available in 275 back and 255 front. Also, I am thinking of staying w/ 40's....the ride is better and my speedo will be accurate.

Do I need to go 35's?

 

better to have more grip than not enough grip

go as wide as you can

 

Ummm.... ...Have you ever seen a 285/30/18 mounted on a 18x8.5" rim, or a 315/30/18 mounted on a 18x9.5" rim or driven a 500+whp Z or G with these tires on them at 170+mph? They work great, and I would not trust my life with something that was not safe at these speeds.

Here is some pics.....Doesn't look too wide to me....






Three examples of that tire size...

 

Take a look at the Conti Extreme Contact tires. They are all season, have twice the treadware and cost half as much as the original Mich's. They have the same speed rating as well. I put a set on my 6spd coupe and have put over 40K miles on them so far and the car is still on rails.

 

Ok, chill out buddy we are not comparing ***** size here, just trying to help some one out on a decision. I am very familiar with that kinda speed and power.

Those pics don't look too bad. It also depends on the brand you get too. For example a Nitto 555 315 will fit smaller on a rim than a Goodyear GSD3 315. It looks like you have a good setup, wide meat with not a lot of bubble look.

 

Hahaha, I am not trying to compare anything . Its cool, and yes, the brand (and make) does make a little difference as far as sizes go. here is an example (pics below) these are all the same size tire (315/30/18) The widest is a Nitto NT01, and the narrowest is a Perelli corsa. I have found that the wider tires are the Michellin Pilot Cups and the Nitto NT01's, and the narrowest are the Michellin Pilot sports and the Perelli's

 

Good pics/comparison.