315’s on fox body rubbing

[Warhorse Racing]

This info might help you make the decision between swapping to Fox axles to keep the 315s or changing rims/tires...

All Fox Body Mustangs came with "factory-installed" understeer. That means the front tires lose grip before the rear tires lose grip. When you install staggered wheels and tires, you ADD understeer. I'm not sure what size tires you have up front, but, even if you were able to fit 275s up front, a 275/315 setup isn't ideal. If you have 255s or 245s, the understeer will be even worse.

This comes into play for performance driving, but also when making evasive maneuvers when daily driving.

If you've made mods to the car to get it "neutral" (negative camber up front; larger rear sway bar), a staggered setup will essentially erase the benefits of those mods.

In your case, stiffening the rear suspension isn't the best option. While it is common to reduce traction in the rear (ADD oversteer) to balance out a car that has understeer, you will be adjusting to a limit of traction that is further IN than stock. Basically, the car might be closer to neutral, but it will lose grip sooner when you push it. Your goal is to get the car neutral with the limit of traction as far OUT as possible.

Stiffening up the rear shocks will also increase "throttle-induced" oversteer, which means you won't be able to put the power down coming out of turns. You'll be taking away the benefits of having 315s. Limiting rear suspension travel will also increase "throttle-induced" oversteer.

I completely understand that people love the look of a staggered setup on these cars. But, I always try to make sure they're aware of the handling issues a staggered setup creates.

I have 18x9" rims with 245/40/18 tires on my 1992 GT autocross car. It has a fair amount of suspension work, but it has a solid rear axle, and it doesn't have coil overs. I adjusted the suspension to make the car neutral. That setup has proven to be faster than cars with larger tires (and faster than a few s550 Mustangs) on an autocross course.

From a handling standpoint (performance and daily driving), I think you'll be better off with a square setup.

 

[1hot87gt]

Qa1 adjustable rear coil overs. Turn them up to a high setting. Limits travel of suspension which doesn’t make for the best ride, but it should solve your problem.

These are my 315’s on 17x10 SC replica wheels. No rubbing.

 

[1hot87gt]

I should add there is a lot of other stuff going on there. First of all Bilstein quad shocks which are very narrow. ARP long wheels studs so I could run a Baer 1/2” wheel spacer. And like I said the QA1 coil overs set on 6 I think which really limits the amount of rear travel downward. Very close to the coil overs, quad shock and exhaust pipe on the inside but all fits and didn’t have to take a hammer to the car or roll the fenders. Overall pretty happy with it.

 

[1hot87gt]

 

[2000xp8]

I have qa1 adjustables in the rear.
I experimented with the settings (not to prevent rubbing, as i said function shouldn't suffer for form) and that is where i got my vomit worthy reference.
I think mine are 10 or 12 way. At one point it rode so bad i didn't even wait until i got home, i pulled into a parking lot and dialed them back.

You also must take into consideration what hard cornering will do. Again, i prefer not to give up function. The rear can move like 2 inches under load.
It's the original reason i purchased a panhard bar to limit side to side travel.

 

[mark007]

As usual I dig into a thread with good info too late. I'm trying to get my foxbody suspension lined out againafter many years in hibernation, but seeing right now I may have made an error. I see what Warhorse is saying about understeer/oversteer in relation to staggered wheels, but I too am running a staggered setup. 265 upfront and 315 in the rear. I was just on the phone with MM Tuesday inquiring about a Torque Arm and Adjustatble rear sway bar to help me achieve a more neutral balance for mixed driving. If what Warhorse is saying is correct, I may have just set myself up wrong before I even hit the street. These two were the last pieces of the MM catalog that I needed. Won't know if this all correct til the driveline and interior go in. I don't have the luxury to go to foxbody mustang axles, as the Lincoln Mark VII has longer axles to begin with. In the pic below I'm running a 1/2 inch spacer to get the tire to sit as it sits now. I have Koni adjustables in the rear, set on a soft setting. My MM panhard bar does it's job keepig things from rubbing for the most part. Old pic before the tear down 8 years ago.

 

[Rdub6]

There are many performance cars coming from the factory with staggered set-ups. So with the right parts I’m sure it’s possible to get it set up correctly.
I guess a staggered set-up on stock suspension is where it causes issues?

 

[mark007]

There are many performance cars coming from the factory with staggered set-ups. So with the right parts I’m sure it’s possible to get it set up correctly.
I guess a staggered set-up on stock suspension is where it causes issues?

Just imagine today's R&D program on yesteryears Foxbody line. Totally different chasis and suspension.

 

[CarMichael Angelo]

Reducing wheel width is the bandaid approach to fixing the problem.The fix is to get the right length axle and gain back the correct wheel spacing. As long as you are running an axle that is too long for the section width of the vehicle, you can expect that a wheel/tire combo of any substance is gonna rub. Restricting the rear end travel to keep it from hitting a tire that is in a direct interference path with the wheel lip is a preposterous solution to preventing that.
As stated,..that solution harkens back to the 70’s, where there was always “ that guy” running a pair of Air shocks inflated to max lift, with a pair of hideous N50-15’s on a Keystone Klassics stuffed on the rear, hanging out about 3” on each side
Lookin all kinds of stupid an sht.

 

[Rdub6]

 

[Mustang5L5]

Looks like a cat in heat

 

[Warhorse Racing]

I'm going to respond to multiple posts, and hopefully add some more helpful info...

Many modern performance cars come with a staggered setup, because they are designed to function best with that setup. Mid-engine and rear-engine supercars are a perfect example. Mustangs come with understeer because Ford believes that is a safer tendency for the driver to have to deal with. The first mod most people make when autocrossing newer Mustangs that come from the factory with a staggered setup is to install a square setup. There are multiple reasons for this, but dialing out understeer is a major one.

The limit of traction (front and rear) is something you control with your suspension mods, suspension adjustments, and driver inputs. Chassis mods are important too. It's very easy to make our Mustangs handle better, but it's also easy to make them handle worse. Making the suspension too stiff is the most common way to make these cars handle worse.

Adjustable suspension components are key when trying to compensate for a staggered setup. The bigger the difference between the front and rear tires, the harder it is to get the car to handle its best. I'm adding a video that covers how I adjusted the suspension on my 1992 GT autocross car. The Steeda adjustable rear sway bar has been discontinued, but, depending on how you intend to use your car, a 25mm rear sway bar, Panhard bar, or Watt's Link can be used to move the limit of rear grip further out.

If you have any questions, please ask.


View: https://www.youtube.com/watch?v=9HiS-t4_O_w&t