Front Tire Rubbing Issue

[scott524]

I have been trying to find a Thread that answers my questions and have been unsuccessful. Instead I decided to start a new Thread and I apologize for any redundancies.

I just completed my build of a MARK III and I am just awaiting paperwork to make it street legal. I have been driving the it around the neighborhood in the meantime and have been having some front tire rubbing issues. I have performed an initial front end alignment using a SPC Pro-Series FasTrax Camber/Caster Gauge and plan to adjust accordingly after I've been able to get it on the road more. The car is basically 1991 Mustang GT donor car with a 4 to 5 lug conversion. Ride height is set at 4.5" measured from the 4" frame tubes at all four corners.

Here is the tire/wheel setup I am running:
- American Racing Torq Thrust Wheel 17”x8” Vintage
- 4.5" backspacing
- 245/45 ZR17 95W Nitto NT 555 tires
- The tires stick out about 1/2" outboard from the fender on the front (equally on both sides)

I called FF prior purchasing this tire/wheel combination and FF informed me I should be ok and may have some issues with rubbing if I were to hit a bump while turning. Unfortunately, the rubbing is happening when I hit a bump going straight.

I've read on the forum about wheel/tire combinations and I seem to be within the norm for tire size. My only concern is the 4.5" backspacing (FF recommends nothing greater than 3.75" up front). Is my problem the backspacing or can this issue be mitigated with alignment or suspension adjustments? Any help would be greatly appreciated as I would prefer to keep the same tire/wheel combination.

Thanks.

Scott

[Jim Schenck]

Scott,

The recommended backspace for that size wheel should be 5.5 inches, 4.5 is going to put the wheel outboard by around an inch. If you are set on using those wheels you could convert to a pin drive front setup, shoot me an email at Jim(at)Factoryfivedotcom and I can help you figure it out.

[CraigS]

Two other thoughts: 1- I am not sure about your MkIII but some of the FFR frames had two sets of holes for the LCA where it bolts to the frame. If yours has these, move it to the inner pair of holes. This will require shortening the UCA. There are two options there. a- buy shorter sleeves or, b- drill new holes for the UCA also. This is assuming that you are mounting the UCA on the near horizontal mounting plate and haven't done an SAI mod. I assume no SAI mod since you mention Fox spindles. My MkII has two sets of holes for the UCA but just one set for the LCA so both of these have been done at various times. 2- Crank in a bunch of negative camber. Yes it wears out the inner edge of the tire but at the 2000-4000 miles per year we usually drive these, it's not that big a deal. Oops, number 3- Install stiffer front springs. I suspect your car came w/ 450 to 550s. 650 to 700 will have only a small impact on the ride.

[Mark Dougherty]

With the donor front a arms you cannot move them inboard
they will hit the 2x3 down tube
BUT
If you purchase a pair of FFR front lower A arms
you can then move them to the inboard set of holes, realighn the car and you are all set.