Need help with proper backspacing..86GT W/Cobra brake upgrade

[RBRANDX]

Ok, I know someone should be able to help me out with this one..My 86 GT had been converted over to the 13" Cobra brakes using 95 GT spindles and the North Racecars rear brackets. The stock length Fox body axles were retained, leading me to this question....What do I need to do/what wheels/backspacing will I need to: A. get a 275/45/17 tire on the rear ( without rubbing, obviously) B: even out the stance. The front wheels are sticking out slightly more than the rears, due to the SN95 spindle/stock length axle combo.

To give as much information as possible about the car, the current suspension setup consists of FRPP "c" springs, Tokico shocks and struts ( blue ones), rear quads removed, maximum motorsports ride height adjustable LCA's, FRPP heavy duty UCA's, stock front and rear swaybars, and UPR c/c plates. I am running 95 GT "three spoke" 17" wheels with 245\45\17 tires and all four corners.

The wheels I have been considering are either the anthracite Bullitt wheels, 03-04' SVT Cobra wheels, the 10th Anniv. Cobra wheels, and finally the FR500 wheels.

I hope this is enough info....I want to order some wheels and tires by the end of the day, so your help is greatly appriciated! Thanks!

 

[RBRANDX]

Anyone...

From the reasearch I have done since I posted this, I am hearing that in order to run a 9" wide rim in the rear I should have the correct length axles....My main concern is getting the front and rear track width as close to even as possible but without having any clearance issues with the 275 rear tires.............HELP!!!

 

[1991vert]

SUPPOSEDLY the sn95 spindles keep the stock track width. i will be running 18x9 rims and a 275/35/18r tire. hopefully all goes well. if rubbing occurs, i guess you could use a spacer

 

[Reed]

The front track width in Fox cars is slightly wider than the rear track width to begin with. Go with 94-95 axles if you have the money to spend, you will be able to fit the 9 inch wheels no problem, especially with the quads removed.

96-98 axles will work and look fine with 17x8 wheels. I am not sure how much further a 9 inch wheel would sit out but the 94-95 axles should look fine.

 

[1991vert]

The front track width in Fox cars is slightly wider than the rear track width to begin with. Go with 94-95 axles if you have the money to spend, you will be able to fit the 9 inch wheels no problem, especially with the quads removed.

96-98 axles will work and look fine with 17x8 wheels. I am not sure how much further a 9 inch wheel would sit out but the 94-95 axles should look fine.

get ready to roll the fenders

 

[Redfire 05]

I don't know if this helps or not, but I went with the ranger axles, for the stock track width, and 98' Mustang GT split rims (17x8) with 275/40 17s on my 86' GT and the fit is perfect. So if you can find out what the backspacing on those rims is you can calculate the backspacing you will need, because the SN95 axles increase the track width by 3/4" if I remember correctly. I suppose I could measure the backspacing on those rims tommorrow after work if you need me to.

 

[Reed]

get ready to roll the fenders

Yeah, yeah, but no other suggestions right?

Anyway, I did some research and 91's right, I was talking crazy before. Stay with your stock length axles if you're going to be running one of the Ford 9 inch wheels. I believe all the ones you listed have a 6.25" back space. Using the wheel alone will increase your track width by 0.66" per side or about 1.32" overall. If you go with a Ford 8 inch wheel (like the Bullitts) they have a 5.72" back space. They will increase your track by 0.19" per side or about 0.38" overall. 275s should still fit and your ride height adjustable LCAs should help you out some if you get in trouble. Anyway, hope that's not too crazy this time and good luck!

 

[RBRANDX]

Thanks for all the good info guys! So here's the plan..... I am going to go ahead and order the 275 tires for the rear and just go with the 17x8 wheels that I have for the time being. I have heard that technically you should have a 9" wheel to run a 275 tire, but if you guys are doing it with no problems...why would I be any different??

Redfire, I believe the stock 98 wheels you have and the 95 wheels I have are the exact same size, right? And since you have the exact same brake setup as I do, what did you have to do to get good pedal feel? I am using an sn95 booster and master cylinder and just can't seem to get the pedal fel just right...it feels like there just isnt as much "bite" as there should be...let me know how far out you adjusted the pushrod and how you have your adj. prop. valve set up. Thanks!

 

[Redfire 05]

Redfire, I believe the stock 98 wheels you have and the 95 wheels I have are the exact same size, right?

Probably, but I'm not sure.

And since you have the exact same brake setup as I do, what did you have to do to get good pedal feel? I am using an sn95 booster and master cylinder and just can't seem to get the pedal fel just right...it feels like there just isnt as much "bite" as there should be...let me know how far out you adjusted the pushrod and how you have your adj. prop. valve set up. Thanks!

Actually I still have to fool with the brakes some because the pedal is to stiff. I'm using the SN95 master cylinder and booster like everyone said you should, but it doesn't feel great. In fact no matter where I adjust the rear brake bias to my rears stll lock up first. However, I think you can adjust the rod length on the front of the brake booster to change the pedal feel, but you have to remove the master cylinder to get to the rod. So I still haven't done it yet.