2G FWD Tire Clearance ???

[aves911]

I've been playing around with some different wheel and tire combos for my FWD, but before I buy anything I want to make sure that I'm not going to run into any major problems. It is important to know that I am only talking about the front wheels and tires as I am going to be running narrower tires in the back to try and better balance the car.

Pretty much, I know that people are running 245 and 255 series tires without any real problem. With these widths, does the tire stick out of the front wheel wells? If it does, how does this affect the suspension travel up front? i.e. instead of the wheel going into the fender under jounce would it hit the outside lip of the fender? Would that result in an appreciable loss in suspension travel?

I know that you can fit a 10" wheel up front with an offset of 10-20. So theoretically you can run a 275 tire. I do know that will fit, but because the wheel sticks out, would you have to either have to a) raise the car up to allow proper travel or b) keep the car lowered and run stiff springs (600-900lb)?

I would really like some feedback from people with experience with wider tire sizes.

Also to note, I know DG uses 275 tires, my car is not his car, so please don't just reply and say it can be done. I'm looking for opinions on the feasibility of putting together a setup like this.

Thanks

 

[ACM]

With the right wheel offset, rolled rear fender lips and tyre OD, 245 section will definitely clear everything, including on a lowered 2G. I believe 255 may fit as well, though I have not tried them personally.

275/40.17 requires raised ride height and stiff springs, and may require fender modifications as well. The OD is ~25.5"

285/30.18 absolutely requires front fender modification, but if that's done the ride height can remain the same as when running 245/45.16 tyres, as they share the same OD.

You need to be a little more specific about what ride height you have, what spring rates are available and so forth. By altering the ride height you can run any tyre width you want, as to whether the car will work afterwards is another matter. If you are working within something like ESP regulations, there is a very small window of acceptable ride heights before the geometry is compromised - if you run SM and build your own upper arms, you've opened up a much larger window and have a lot more options.


Bear in mind that for the same tread width and OD, the larger the wheel diameter the heavier the tyre/wheel package, by quite a bit. 245/45.16 on an 8.5 rim can weigh as little as 34lbs without spending a lot of money; move to 245/35.18 on a 9.5" rim and you're looking at over 40lbs a corner even with $2k CCWs. And you still haven't put an extra millimetre of rubber on the track.

Charles

 

[aves911]

I'm sorry, I didn't mean to leave information out.

I'm trying to piece together my new set up all at once, including wheels, tires, and the necessary spring rate so I don't spend a lot and find out it doesn't work together. I'm going to be running GC with hypercoils so ride height and spring rate are adjustable. One quick point, when talking about ride height, I am assuming that is the distance from the top of the tire to the fender?

I'm not competing in Auto-X, just for fun ocassionaly, but I'm really building this car for road racing. Again just for fun. So I'm not concerned about really meeting any regulations, just about making a set-up that will work.

I'm only considering 17" wheels for brake clearance. I was looking at for tire combos

275 f on a 17x10 +12 245 r on a 17x9 +35
255 f on a 17x9 +35 235 r on a 17x8 +42
245 f on a 17x9 +35 225 r on a 17x8 +42

My thinking so far is that if a 275 sticks out and I set my ride height so the fender is 2" above the tire. Then I have 2" of travel before the tire hits the fender. Still trying to find data to calculate the roll stiffness of the RM bars so I can find a good spring rate. But from using sway bar stiffness estimates from one of DG's posts I come up with around a 550-600lb front spring to maintain 1.5"-2" max travel on a 2800lb car under 100% lateral load transfer. Does that sound reasonable? And is this how I would go about making sure the tire would never hit the fender when cornering?

I hope that helps,
thanks for replying
-Jacob