I plan on modding my suspension but have just started doing research on it - it will probably take a while to saort everything out. But I need new tires righ now. Will the size of the tires limit me on what I can do with the suspension?

Also, I can see getting wider tires would provide more traction. But what is the advantage in going from a 17" tire to an 18" or 19" tire ( rim diameter) ? Is there any reason to put more narrow tires on the front than the back?

I currently have 275/40ZR17's in the front and back. I'm considering getting some Nitto 555's 315/35ZR17's or some 285/40ZR17's. I could go to a 18" or 19" tire if that is better.

 

Research has shown you lose handling when your rims go too large, I would stay with 18's all around, then use 9.5inch rim in front and 10.5 inch in back, use the same tire on all four, 275/35's would be good or 285's. Nitto's are good tires, the only reason I see to have more narrow tires on the front is to help with the car tracking straight, not finding ruts in the road, if you look at F1 cars they have a wider front track than rear, this helps with handling, I would not try to make this so for our cars. Also I am not sure how radical you want to be with your setup.

 

F1 cars are rear engine cars, and are rear weight biased (more weight over the rear tires). This setup typically requires more tire on the rear for a balanced setup. If you put the same size tire on the front, you can't use it cause you'll lose your rear before you approach the limit of the fronts. So narrower tires on the front decrease rotating mass and increase front steering response (the heavier and larger the tire, the more gyroscopic effect you have resisting turning). In the racing environment, they aren't so much worried about the front tracking ruts. The race tracks may be rough, but they're rarely rutted. And race cars run such extreme alignment specs that the steering is typically very sensitive and twitchy.

On on front heavy, front engine car like ours, you want all the front tire traction you can get. For a street car that's not being pushed, there's no reason to get extreme. 275 or 285 fronts are fine. If you want all the traction you can possibly get, you can go with 315/35R17s on a 17x11" wheel. These will fit the front about as easily as they fit the rear. You may need a small wheel spacer (quarter inch at the largest) and you may need to do a very small amount of grinding on the spindle. There's a 'nub' on the spindle that may rub, nothing that's going to cause any measurable structural weakening of the spindle. A tire this big on the front will have a noticable affect on how the steering feels though. the only people I know of that run this setup are serious Autocrossers. Some even run them on the street. Once you get used to the increase in available front bite, it's hard to go back. If you're primarily a straight line racer though, this would just be a waste of effort.