I’ve added a table which tells you what track width Mustang II kits will work best on which vehicles. The list will be updated as I get time to go through the thousands of emails asking “what track width should I use on my ________?”

We are often asked about making a Mustang II crossmember kit for a track width less than the stock 56-1/2”. 56-1/2” is the distance from the rotors wheel mounting face to face. Aftermarket brake kits and rotors can change this 56-1/2” dimension. It’s good to have the brake kit, rotors, wheels and tires before deciding how much the crossmember should be narrowed.

Here are the steps I’d suggest:
Read all the way through this for best results.

Use our 56-1/2” kit, for either stock springs or coil-overs. Coil-overs will provide more spring to frame clearance and make it easier to dial in ride height and ride quality.

Get the wheels and tires that will be used.

Get the brake kit and rotors that will be used. (Might as well get the calipers, too, but this won’t affect the crossmember width.)
Mock up the car at ride height and position the wheels and tires, front-to-back and at the desired track width.

Compare the spindle height (the center of the wheel) to the height of the frame at the bottom. Decide on stock or dropped spindles. See https://shared-assets.adobe.com/ link/17afad9a-b219-4191-7cfb-7ee4bfa6277c/?file=Coil%20Over%20Mustang%20II.pdf, page 6, or https://shared-assets.adobe.com/link/17afad9a-b219- 4191-7cfb-7ee4bfa6277c/?file=Coil%20Spring%20Mustang%20II.pdf, page 6 for info regarding this decision.

Decide on stock length or shortened (narrowed) control arms. The upper arm cross shafts on stock length arms will be about 29-1/2” center-to-center with a stock rotor-to-rotor face width of 56-1/2”. When the crossmember gets shortened, the control arms will move closer together by the same amount. See if there will be clearance issues because of this. Shorter control arms will move the pivot point out by their “shortened” amount, given that the spindle location does not change. Shorter arms will mean a slightly choppier ride. Get the upper and lower arms that you decide on.

Mock up the wheel/tire, spindle, brake kit, rotor, and lower control arm. Put the assembly in position in the fender of the mock-up. The tire should be very close to vertical. Make the lower arm level. This can be done on just one side. Measure from the frame centerline to the lower arm pivot and double that dimension. Or mock up both sides and measure lower control arm pivots center-to-center. Subtract the lower arm pivot dimension from 22-1/4” and you have the amount that the crossmember should have removed from between the rack mounts.

It will be necessary to use a shorter than stock rack. Some machine shops will do this and there are aftermarket companies that make custom-length Mustang II racks. Before making the crossmember shorter, confirm that a rack will be available.