1991 Mustang GT SN95 5 Lug Conversion, Wheel Sizing and Offset Questions

DHatton

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Hello,

I am planning to purchase 94-95 Spindles for my 91 Fox GT Vert, and looking to buy Fox-Length rear axles.

I'm installing Cobra front and rear brakes, and removing the quad shocks, and replacing the front and rear control arms for aftermarket tubular control arms.

I'm thinking of going for a staggered tire setup, and I want 17x8.5 wheels in the front, and 17x9.5 wheels in the rear.

The question I am asking is what offset should I go for for the front and rears?

The guys who are selling me these parts say I should go for ET30 offset for the front and rear, but I want Enkei RPF1's, and the rear wheels in 17x9.5 only come in ET18 or ET38.

Could I use the SN95 Axels and run ET38 offset in the rear?

I would like equal track width in the front and rear, and I don't want the wheels to stick out of the fender, but would prefer them to stay in line with the fender.

I am also going to buy adjustable coilovers, and will probably lower the car around 1 inch, depending on my tire setup.

Please let me know, I am new to modifying cars and need some help.

Thank you!
 

KRUISR

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Apr 16, 2015
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The best way to know would be to test fit the wheel you would like. Saying that, here is my thoughts based on my current wheel setup.

20220526_230157.jpg 20220526_230219.jpg 20220526_230706.jpg

My wheels are 18x9 with a 24mm offset. I am also using a 5/16" wheel spacer (8mm). I have fox length axles as well and I rolled the fender lip when I was doing body work before I painted the car. So what is shown in the pics would be equivalent to an 18x9 with 16mm offset with no spacer.

You want to run a 17x9.5 with an 18mm offset on fox length axles. Those rims would put the rim edge approximately 4mm (5/32") further out than I current show in the pics above. The level in the third pic is vertical based on the bubbles and is touching the outer fender edge.

If you used the ET38 offset rims with 94-98 axles you would be almost the same position (only 3mm - just under 1/8" - more outward than my set up shows)

Just my thoughts, hope it helps.
 
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Warhorse Racing

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Are you planning on using this car for performance driving (autocross or track)? If so, there are a few things to consider...

A staggered wheel/tire setup adds understeer to a car that already has understeer. It's not an ideal setup for performance driving.

Choosing the proper bushings in your control arms is important, especially for the rear UCAs/LCAs. You want a 3-piece poly bushing in those positions. Steeda & J&M make UCAs/LCAs with 3-piece poly bushings.

These cars generally handle better when they sit higher than most people think looks good. Lowering the car too much will make it handle worse.

I prefer to keep the quad-shocks in place. Your stock quad-shocks are probably bad. An inexpensive pair of quad-shocks will be fine.

My 1992 GT autocross car has 96-04 spindles. 03-04 Cobra brakes and a 1998 Cobra rear axle. I use 18x9" +30 offset wheels with 245/40/18 tires. My fenders aren't rolled, cut or flared and that setup fits fine. You can see how the wheels/tires fit on the car in this video. There are also many other helpful videos about suspension mods on my YT channel.


View: https://www.youtube.com/watch?v=t3HGcnscKdg
 
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DHatton

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May 22, 2022
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The best way to know would be to test fit the wheel you would like. Saying that, here is my thoughts based on my current wheel setup.

20220526_230157.jpg 20220526_230219.jpg 20220526_230706.jpg

My wheels are 18x9 with a 24mm offset. I am also using a 5/16" wheel spacer (8mm). I have fox length axles as well and I rolled the fender lip when I was doing body work before I painted the car. So what is shown in the pics would be equivalent to an 18x9 with 16mm offset with no spacer.

You want to run a 17x9.5 with an 18mm offset on fox length axles. Those rims would put the rim edge approximately 4mm (5/32") further out than I current show in the pics above. The level in the third pic is vertical based on the bubbles and is touching the outer fender edge.

If you used the ET38 offset rims with 94-98 axles you would be almost the same position (only 3mm - just under 1/8" - more outward than my set up shows)

Just my thoughts, hope it helps.
Hello, thanks for the reply.

Unfortunately I cannot test fit any wheels at the moment, the car is in the garage so I would have to ask my mechanic to do so. The SN95 Spindles and the fox length axels have not been purchased yet, so I can only mount stock wheels to my car.

If I use the ET38 offset rims for the rear with Fox length axels, would they fit without requiring fender rolling?

I want 9.5 inch rears, but if it requires fender rolling I would rather have a less wider wheel.

If the ET38 rims with 9.5 inch width fit, what offset should I run in the front to keep the track width the same as the rear?

I'm happy to run spacers if the rear wheels are too sunk in compared to the front wheels.

If its still too much hassle, should I consider 17 x 9 rears with 35 or 45mm offset, and 17 x 8.5 with 30mm offset?

Hope you can understand where i'm coming from, I just want the widest rear wheel setup without fender rolling, but still want to keep the track width for the front and rears equal.

Thanks again!
 

DHatton

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May 22, 2022
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Are you planning on using this car for performance driving (autocross or track)? If so, there are a few things to consider...

A staggered wheel/tire setup adds understeer to a car that already has understeer. It's not an ideal setup for performance driving.

Choosing the proper bushings in your control arms is important, especially for the rear UCAs/LCAs. You want a 3-piece poly bushing in those positions. Steeda & J&M make UCAs/LCAs with 3-piece poly bushings.

These cars generally handle better when they sit higher than most people think looks good. Lowering the car too much will make it handle worse.

I prefer to keep the quad-shocks in place. Your stock quad-shocks are probably bad. An inexpensive pair of quad-shocks will be fine.

My 1992 GT autocross car has 96-04 spindles. 03-04 Cobra brakes and a 1998 Cobra rear axle. I use 18x9" +30 offset wheels with 245/40/18 tires. My fenders aren't rolled, cut or flared and that setup fits fine. You can see how the wheels/tires fit on the car in this video. There are also many other helpful videos about suspension mods on my YT channel.


View: https://www.youtube.com/watch?v=t3HGcnscKdg

I live in London so there's alot of city driving, and I want my car to be my daily. I do plan to do launches, and to keep the car fast, hence why I was inquiring about wider rear tires.

I don't think I will take it to the track, but I also want the car to perform better than stock, especially in the handling department.

I don't plan on lowering it or slamming it, but I do want to purchase adjustable coil overs as once I fit the tyres that I choose I can adjust the ride height so the wheel sits well.

If I run 17 x 9 wheels in the front and rear, would the quad-shocks still be able to fit? Also, would 17 x 9 wheels rub in the front? I heard that 8.5 wide wheels are the maximum width you can run without putting spacers.

Thanks for helping me out, will check out your YT channel.
 

KRUISR

5 Year Member
Apr 16, 2015
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If I use the ET38 offset rims for the rear with Fox length axels, would they fit without requiring fender rolling?
You would be 22mm (almost an inch) inward from what my pics show. I would be concerned with rubbing something on the inner fender or shock ( I have not looked at mine lately to know how much clearance I have to compare).

If you are running different width rims front and rear, what is your reference for track width - inside edge, centerline or outside edge of tire?
 

KRUISR

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Apr 16, 2015
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If I run 17 x 9 wheels in the front and rear, would the quad-shocks still be able to fit? Also, would 17 x 9 wheels rub in the front? I heard that 8.5 wide wheels are the maximum width you can run without putting spacers.
Depends on the tires you are using.

My wheels are 18x9 ET24 all around. I have a 255/35/18 in front and a 275/35/18 in rear. I have coil overs in front and needed a spacer to not have the rim rub the coil over.

20220129_104729.jpg
Driver front with spacer, otherwise bottom coil rubbed on inner rim lip. Because I am using a tire that is shorter than stock (25.2" diameter vs 25.8" OEM) I don't get rubbing on inner fender like my 245/50/16s used to.

20220524_194917.jpg
pic from this past weekend
 
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Warhorse Racing

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Feb 10, 2019
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I live in London so there's alot of city driving, and I want my car to be my daily. I do plan to do launches, and to keep the car fast, hence why I was inquiring about wider rear tires.

I don't think I will take it to the track, but I also want the car to perform better than stock, especially in the handling department.

I don't plan on lowering it or slamming it, but I do want to purchase adjustable coil overs as once I fit the tyres that I choose I can adjust the ride height so the wheel sits well.

If I run 17 x 9 wheels in the front and rear, would the quad-shocks still be able to fit? Also, would 17 x 9 wheels rub in the front? I heard that 8.5 wide wheels are the maximum width you can run without putting spacers.

Thanks for helping me out, will check out your YT channel.
It's not hard to get the car to handle better than stock. There are lots of different levels to modifying these cars; it all depends on how far you want to go. My Fox isn't heavily modified compared to others and it handles pretty well.

There are a lot of things that factor into whether or not a wheel will fit. And, because no two Fox Body Mustangs were built exactly the same, it can be hard to be 100% certain that the wide setup someone else uses will work on your car. If you check out willtheyfit.com, you can calculate the difference between your current setup and the wheels/tires you are considering. It will give you a sense of how much closer to the strut/quad-shock/fenders your new setup will be.

Coil-overs up front might create a clearance issue, depending on the backspacing of your wheels. I don't use coil-overs on my cars, but I suspect my current setup would hit coil-overs up front.

If you purchase a quad-shock that looks like the OEM version (no cover on the piston), you can flip the quad-shock to create more space for wider tires in the rear.
 

DHatton

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May 22, 2022
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You would be 22mm (almost an inch) inward from what my pics show. I would be concerned with rubbing something on the inner fender or shock ( I have not looked at mine lately to know how much clearance I have to compare).

If you are running different width rims front and rear, what is your reference for track width - inside edge, centerline or outside edge of tire?
My reference for track width would be the outside edge of the tire; basically even width from the fender to the wheel for the front and back. Hope that helps.
 

DHatton

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May 22, 2022
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It's not hard to get the car to handle better than stock. There are lots of different levels to modifying these cars; it all depends on how far you want to go. My Fox isn't heavily modified compared to others and it handles pretty well.

There are a lot of things that factor into whether or not a wheel will fit. And, because no two Fox Body Mustangs were built exactly the same, it can be hard to be 100% certain that the wide setup someone else uses will work on your car. If you check out willtheyfit.com, you can calculate the difference between your current setup and the wheels/tires you are considering. It will give you a sense of how much closer to the strut/quad-shock/fenders your new setup will be.

Coil-overs up front might create a clearance issue, depending on the backspacing of your wheels. I don't use coil-overs on my cars, but I suspect my current setup would hit coil-overs up front.

If you purchase a quad-shock that looks like the OEM version (no cover on the piston), you can flip the quad-shock to create more space for wider tires in the rear.
In regards to how far I am willing to go to upgrade my suspension/wheel setup. I'm planning on doing a full suspension build with tubular K-member, tubular front and rear control arms, and adjustable coil overs. I've also considered getting the North Race Car Brackets so I can fit a larger tire in the rear.

I also wanted to ask if 17 or 18 inch wheels fit better, or perform better. I'm still having a hard time deciding.

I am also not sure about the quad-shocks being a necessity; if I remove them or flip them to make space for a wider tire, I heard that it doesn't effect wheel hop if you have aftermarket control arms + coil overs, is this true? If my setup allows the quad-shocks to remain, do you know any good brands?

In your opinion, do you think equal width front and rear tires are good enough for the street? I'm starting to have doubts about staggering my tires.

Thank you!
 

Warhorse Racing

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Feb 10, 2019
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I like helping people improve the handling of their Mustangs, but I want to state emphatically that I don't endorse aggressive driving on the street. Finding out how capable our Mustangs can be is a lot of fun, but it should only be done in a safe and controlled environment.

You mentioned that you are new to modifying your car. You are bound to make some incorrect adjustments as you dial in your setup. Pushing an incorrectly adjusted car on the street can lead to injury or death. I strongly encourage you to find a local car club and attend some autocross or track events. I'm not trying to be rude. As an instructor, my first priority is safety.

I've spent the last few years trying to show people that they don't need coil-overs and an aftermarket K-member to make their Mustangs handle well. I don't deny that those parts will absolutely improve the performance of a Mustang. My experience tells me that the gap is not as wide as most people think between a coil-over setup and an OEM-style spring setup. Many people will disagree with me on that (and I hope they add their advice to this thread).

Because I don't daily-drive my cars, and because I don't have experience with using coil-overs on the street, I might not be the best person to help you with that part of your build.

I prefer 18" wheels, but many people prefer 17" wheels. Overall tire diameter does impact the performance of your car, so you will have to determine which size works best for your specific application.

The quad-shock debate has been going on for years. I've driven cars with them and without them. I prefer to have them in place. Many people will disagree with me about quad-shocks being effective. Koni makes quad-shocks that don't have a covered piston; they are pretty expensive.

I wouldn't use a staggered setup on a 79-04 Mustang for safe street driving or for autocross.

I hope this info helps.
 

DHatton

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May 22, 2022
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I like helping people improve the handling of their Mustangs, but I want to state emphatically that I don't endorse aggressive driving on the street. Finding out how capable our Mustangs can be is a lot of fun, but it should only be done in a safe and controlled environment.

You mentioned that you are new to modifying your car. You are bound to make some incorrect adjustments as you dial in your setup. Pushing an incorrectly adjusted car on the street can lead to injury or death. I strongly encourage you to find a local car club and attend some autocross or track events. I'm not trying to be rude. As an instructor, my first priority is safety.

I've spent the last few years trying to show people that they don't need coil-overs and an aftermarket K-member to make their Mustangs handle well. I don't deny that those parts will absolutely improve the performance of a Mustang. My experience tells me that the gap is not as wide as most people think between a coil-over setup and an OEM-style spring setup. Many people will disagree with me on that (and I hope they add their advice to this thread).

Because I don't daily-drive my cars, and because I don't have experience with using coil-overs on the street, I might not be the best person to help you with that part of your build.

I prefer 18" wheels, but many people prefer 17" wheels. Overall tire diameter does impact the performance of your car, so you will have to determine which size works best for your specific application.

The quad-shock debate has been going on for years. I've driven cars with them and without them. I prefer to have them in place. Many people will disagree with me about quad-shocks being effective. Koni makes quad-shocks that don't have a covered piston; they are pretty expensive.

I wouldn't use a staggered setup on a 79-04 Mustang for safe street driving or for autocross.

I hope this info helps.
Thanks for your advice; just to clarify this car will be for street driving, but I'm not going to do burnouts at stop lights or hoon the car around. I want better handling since the car doesn't have ABS, i'm not the most experienced driver, and UK roads are subject to worse weather conditions than the US as a whole.

I understand your point of safety, and I agree. My interest is to have a good handling car, as I feel it would keep me more safe, and there's a less chance of my car going on a mustang crash compilation.

I'm getting my mechanic to install everything for me, and I have advice from the parts store to see what will fit in addition to asking questions on the forum.

I'm probably going to go for 17 x 9 wheels in the front and rears, since I can make the offset equal and ensure easy fitment; I don't think .5 inches will make much difference in performance, and honestly the staggered setup is cool, but I would rather prioritise handling and ease of installation without overly modifying my car.
 

Warhorse Racing

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Feb 10, 2019
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Thanks for your advice; just to clarify this car will be for street driving, but I'm not going to do burnouts at stop lights or hoon the car around. I want better handling since the car doesn't have ABS, i'm not the most experienced driver, and UK roads are subject to worse weather conditions than the US as a whole.

I understand your point of safety, and I agree. My interest is to have a good handling car, as I feel it would keep me more safe, and there's a less chance of my car going on a mustang crash compilation.

I'm getting my mechanic to install everything for me, and I have advice from the parts store to see what will fit in addition to asking questions on the forum.

I'm probably going to go for 17 x 9 wheels in the front and rears, since I can make the offset equal and ensure easy fitment; I don't think .5 inches will make much difference in performance, and honestly the staggered setup is cool, but I would rather prioritise handling and ease of installation without overly modifying my car.
I'm glad to hear that you don't plan on driving aggressively on the street. In my opinion, the key to building a Fox Body to be a capable and safe street car is to eliminate the "factory-installed" flaws. Get the car neutral with adjustable shocks & struts and a larger rear sway bar; don't lower the car too much (less than 1", especially up front); and settle the nervous rear end with good UCAs/LCAs. Make sure your rubber bushings, tie rods and ball joints are in good shape. And approach any mods with the understanding that oversteer and understeer aren't always a tendency of the car/setup, they are often driver-induced.

When you choose tires, make sure they have good ratings/reviews for driving in wet conditions. No amount of suspension upgrades will make certain tires work well in the rain.

There are many different opinions about how to modify these cars. People tell me I'm doing it wrong all the time. Keep asking questions and don't feel pressure to make every modification under the sun. A properly adjusted Mustang with fewer mods will perform better than an improperly adjusted Mustang with more mods.
 

Willybill32

But at least it's tight!
Jul 16, 2019
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I have 17” pony wheels from LMR.com on my ‘86 GT, 8” in the front and 9” in the rear. Rear tires are 275/40X17. I installed new Bilstein quad shocks and reversed them for tire clearance. I also have approx. 1” lowering springs installed and have no clearance issues.

Bill
 

DHatton

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I have 17” pony wheels from LMR.com on my ‘86 GT, 8” in the front and 9” in the rear. Rear tires are 275/40X17. I installed new Bilstein quad shocks and reversed them for tire clearance. I also have approx. 1” lowering springs installed and have no clearance issues.

Bill
What tires are you running in the front?

Everyone says if you run 245/40/17's with 17x9 wheels in the front, you'll get rubbing and have to roll the fender or run spacers...I'm happy to run 17x8 wheels in the front if I don't have to modify anything (apart from the 5 lug conversion etc.)

I plan to keep the ride height the same for now.

Thanks for your input.
 

Willybill32

But at least it's tight!
Jul 16, 2019
422
194
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Lexington, KY
What tires are you running in the front?

Everyone says if you run 245/40/17's with 17x9 wheels in the front, you'll get rubbing and have to roll the fender or run spacers...I'm happy to run 17x8 wheels in the front if I don't have to modify anything (apart from the 5 lug conversion etc.)

I plan to keep the ride height the same for now.

Thanks for your input.
My front combination is 17x8 with 245/45x17 Nitto tires. I haven’t noticed any rubbing.

Bill
 

Mustang5L5

Put lubricant all over the balls
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17x8 all around.

235/45/17 up front, 255/45/17 rear. 94 spindles up front and 94-98 sn95 axles out back. On coil-overs. Minor rubbing on the rear fender lips.

I believe these are 5.72” BS, +30 offset. You could use an online wheel offset calculator to use this as a baseline and calculate your desired wheels.

I could fit 245/4517 up front. I’ve tried it and it works. Next set of tires.

CBB6BFE8-A559-40AC-8A28-9DA7F5AA7AEE.jpeg
 
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DHatton

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May 22, 2022
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17x8 all around.

235/45/17 up front, 255/45/17 rear. 94 spindles up front and 94-98 sn95 axles out back. On coil-overs. Minor rubbing on the rear fender lips.

I believe these are 5.72” BS, +30 offset. You could use an online wheel offset calculator to use this as a baseline and calculate your desired wheels.

I could fit 245/4517 up front. I’ve tried it and it works. Next set of tires.

CBB6BFE8-A559-40AC-8A28-9DA7F5AA7AEE.jpeg
Nice car, is it lowered with your coilovers?

I'm planning on keeping the wheels size the same front and back (17x9), but I'm still not sure whether they would rub or not.

With your setup and fox length axels, do you think I would get rubbing with 275's on the rears on a 17x9 or 17x8 wheels?

Would I be able to run 17x9 wheels front and back, with 245 front's with no rubbing issues?

I don't plan on lowering the car yet or getting coilovers as unfortunately I've ran out of money.
 

Mustang5L5

Put lubricant all over the balls
Mod Dude
Feb 18, 2001
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Yes, front MM coil-overs in that pic, with conventional springs and adjustable height arms out back.

With the 235/45/17 up front, i have no rub, even lowered. However with 245 i have slight rub but livable. I'd rather have the extra rubber up front for braking
 

DHatton

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Thanks for the info; I was envisioning a very similar setup.

For the MM coilovers, were they divorced or true coilovers? Would I also need to get new front control arms and a K-member? What spring rate and amount of coils would you recommend, and what are you running?

Are you also running aftermarket shocks + struts? Some MM coilover kits I see on their store are only compatible with Bilsteins, Koni's etc.

For the 245 front rub, would a couple of steering rack limiters fix this? I'm not sure how much it would affect the turn rate to fit the fatter tire.

Thanks for taking the time to reply.