Hey all,
I just put a T-bird Turbo rear end in my 1990 GT and have now gotten confused when looking at wheels. After bolting the new rear end into the car, it is a bit wider than the stock one (which I new going into it). It also seems to stick out a bit to the passenger side (not a crazy amount and I am hoping will go away once the car is driven a little). My initial plan was 17x9s in the rear, but now I am realizing 17x8s might be all I get, which is fine. I currently have 15x7 turbines and apparently the backspacing is 4.875 and offset is +22mm. This offset/backspacing thing confuses the $h!t out of me so I have still not figured out how that calculates, but that's what all the specs say so I'll go with it. My real question is this: What would the specs be of a 17x8 wheel that does not stick out any further, preferably tucks in a little more?

Based on the backspacing of my 15x7s being 4.875, that leaves 2.125" outside the axle flange. SO, I can figure 8" - 2.125 = 5.875" of backspacing. I plugged this into a offset/backspacing chart and came up with an offset of +38mm. Does that even exist? Am I completely wrong on my calculations? Like I said, the whole thing confuses the crap out of me so I could use some help. I have not seen any +38mm wheels for the Mustang so I feel like I messed up somewhere.

Also, I would love to hear from some people who have swapped in the T-bird disc brake rear end to see what they are running.

Thanks a bunch in advance for any help you can give.

 

Too many numbers for me to get my head around... lol

Take a pic looking down the side of your car like this:


This will help us get a feel for the clearance you may have. Also, if your axle got wider, as it appears to have done, than you don't need narrower wheels, just a larger off-set to "move" the wheel inward and more under your fender. The wheel well space has not changed, just the location of the wheel needed to fit within it.

The Fox Body, typically is able to run a 9" wheel with a 245 tire and no problems. A bit more tire/wheel can be installed, but rubbing becomes a bigger concern.

Can you measure the length of the NEW axle and compare it with the original one. I can use this info to figure out how much additional back-space you need to install a 8" wheel.

Jazzer

 

The new axle is 1.5" wider than stock ( 3/4" on each side ). Also, the quad shocks are currently NOT installed due to a slight difference in mounting locations on the new axle. They can be retrofitted in, it would just require measuring/drilling/etc... so I was going to see how it handled without them.

The car is up on stands in the garage so the pics are not as good as yours but I hope they will work. I know they are sideways and I apologize, my phone ALWAYS flips the photos around.

 

http://www.flickr.com/photos/6266091...7680/lightbox/

http://www.flickr.com/photos/6266091...1225/lightbox/

(OK, maybe this will work. Not ideal, but I did manage to rotate them correctly.

 

OK... if you have 3/4" longer axles on each side, this means an additional positive off-set of 16mm. So if the NORMAL off-set for a 9" wheel on a Fox Body is +18mm (5.71" back-space), and it is, then the off-set you need is going to be about +34mm (6.46" back-space).

This is looking like an off-set for an S197, BUT.... you still have 4x4.5" lug pattern, right? You need to look for a 9" wheel with just a bit less than 6.5" back-space and your set

Jazzer

PS. Your links don't work for me, as the page never loads

 

Right on, that helps. I will start looking for those wheels, and with any luck i'll find a set that looks good and doesn't cost an arm and a leg. This is a pain, but I really appreciate the help. I will try to fix the picture issue so you can see where the back tires sit. They are basically right to the outer edge of the wheel opening at the top, wouldn't want them sticking out any further.

 

What you describe is what I picture, in terms of where the wheels sit. I suspect that they may be damaged by the fender if you drive it and can possibly damage the fender with the tires! Sounds as if you have not yet driven the car and think that you should read a little trick of mine BEFORE you do.

Head into Choosing a new tire and look to a section called... "I want fat meats", or some such. I have a paragraph in there to determine wheel clearance to fenders and such to make sure one does NOT rub, when purchasing wider wheels/tires. Your issue is a bit off that mark, but will be helpful to you fo sho

Jazzer

 

Great write-up. I have not driven the car as I am still in the process of installing a new proportioning valve for the new rear disc system. I just put the calipers and pads on today so the car is still up on stands. I can however (and will tomorrow) jack each side of the rear axle up to the bumpstop and check all around for clearance. I will post up my findings. You are a great resource and I appreciate all the assistance.


Just trying this picture thing again:

http://www.flickr.com/photos/6266091...1225/lightbox/

 

You are more than welcome

A little thought on a rear prop valve, as I have one. With the OEM suspension geometry, I would not expect a whole lot more rear braking power, but some for sure. I am curious, does the Fox have a poor front/rear bias in this regard? Typically, the 4-link cannot handle a whole lot of additional brake power without locking up or triggering the ABS system. You don't have ABS, but just some food for thought.

Jazzer

PS. Linky still no worky