Big front tires

[RobNoLimit]

I've seen a few Pro-Touring and Autocross cars with some pretty big front tires. If you throw out body fit as a concern, are there any negatives? I'm talking about 305/315 and even 335. Any thought and/or experience would be great. Thanks.

[tazzz25906112]

Rob you may experience some hunting on hwy driving where the car wants to flow the ruts trucks make in the road.... They say that it is also largely effected by camber setup...

[RobNoLimit]

Hmm, thats makes sense, but I would think that modern caster settings, 7 to 9 deg, may minimize the hunting?

[ProdigyCustoms]

We have done lots of 295s and they do hunt a little. A lot of caster does help but can put a lot of strain on the low speed steering. And now we begin to touch on the compromises of Pro Touring / Racing.

[RobNoLimit]

I currently run 285/35/18 fronts, on 11" wide wheels. I have 335/30/18 on the back. Standard alignment is 1/2* neg. camber, 7 1/2* caster, and 1/4" toe out. I usually have appx 35 lbs + spring load on the pass ft tire (swaybar unhooked), then nuetral the bar with me in it. It drives with one finger, and has no hunt or wander. I'm just wondering, Where is the line on front tire size? or is there one? I was going to swap wheels and try it but the backspace is wrong, and the inner lip hit the steering arm. Also, a swap like this would reduce scrub radius from 3.418 to 2.918. Any thoughts on this?

[Nessumsar]

I would think that there is almost no downside to running the largest possible front tire, all things considered. Especially if (in your case) in doing so you can reduce your scrub radius without limiting turning radius.

[Rod]

do it Rob run a big FATTY tire up front

[RobNoLimit]

I would think that there is almost no downside to running the largest possible front tire, all things considered. Especially if (in your case) in doing so you can reduce your scrub radius without limiting turning radius.

How is your car with the 315's? Have you done much freeway driving? BTW, are you going to Del-Mar?

[rrunner68]

The only time I have any real issues is if the highway is seriously rutted, especially on major trucking roads like 5, 8, 395, etc. When I'm in the slow lane, if it hooks a rut, it sucks. I'll usually drive in the fast lane and move over so the speeders can pass, then jump back in the fast lane. Driving long hauls on trucker roads can get really annoying. But I think that's where Al hit the nail on the head, low profile tires, high spring rates, stiff shocks and sway bars equal out to a less than pleasurable driving experience on crappy roads (California).

[Nessumsar]

How is your car with the 315's? Have you done much freeway driving? BTW, are you going to Del-Mar?

It hunts a bit on the hwy way; but most of that I'm sure can be attributed to the bumpsteer, 5* of caster, and the worn out steering box.

Matt and I will be coming down to Del Mar on Saturday to spectate.

[BuddyP]

Great thread. After seeing ridetechs new tie rod offset kit I started pondering going from an 245 tire up front to a 275. Wondering if it is worth the $$. I haven't bought wheels yet.

[SLO_Z28]

The front tire is unique to every car, and is determined by a lot of things. I will say that the corvette guys are faster with smaller diameter wheels, and tires with less section width in racing. They will be .025-.5% a lap faster with a 275/17 hoosier A6 over the 315/17 hoosier A6, and 2% faster than the factory 315/18 tires. Point being that a car must be engineered as a system. You have to look at things like recripocating mass, scrub radius, ackerman, and overall wieght and wieght transfer before deciding on tire sizes.