Foxbody Irs Alignment

[sab24711]

hey I have recently installed a cobra irs into my 88 gt. Just did the alignment at a friends shop. We had to enter a 04 cobra so the machine will register the rear sensors. We used that to align the rear, the camber was spot on just had to adjust the toe. My problem is now my right rear tire rubs.

I’m just wondering how others Fox irs owners adjusted their rear ends

 

[90sickfox]

That's the way I've been doing it for the last 10+ years. The fox bodies aren't really exact from left to right. I guess Ford used a wide margin for body alignment specs.

Do you have the correct 45 or 50mm offset wheels on the rear of your car ?

What size tire....and what size rim ?

 

[FoxMustangLvr]

Hmmm, I have not done a proper alignment on my car since my IRS install. Maybe I should do that this spring.

@sab24711 What wheel & tire size are you running? Offset? Have you rolled your fenders?

 

[Mustang5L5]

I need an IRS.

 

[a91what]

Me too.

 

[General karthief]

’m just wondering how others Fox owners adjusted their rearends

Fixed
Now thats ct material right there.

 

[sab24711]

That's the way I've been doing it for the last 10+ years. The fox bodies aren't really exact from left to right. I guess Ford used a wide margin for body alignment specs.

Do you have the correct 45 or 50mm offset wheels on the rear of your car ?

What size tire....and what size rim ?

I have 18x9 45mm offset Saleen wheels for a 10-15 mustang. Running a 245/40r18 tire?? I think, I need to double check that.

Normally the 18x9 have only 30mm offset but I bought a 10” wide rim that has 45mm off set and cut it down to 9” so it would fit.

I might measure the inside of the wheel in comparison to the wheel well and see if I can remove some of the hub face. Try to get the wheel to sit further inside.

 

[sab24711]

Hmmm, I have not done a proper alignment on my car since my IRS install. Maybe I should do that this spring.

@sab24711 What wheel & tire size are you running? Offset? Have you rolled your fenders?

Yes I have rolled the fenders and to the extreme too. Made sure of that before paint/body work. I was driving around without an alignment in my car for a while now. I figured it would be hard to explain to a tech that I need an alignment for a car that’s 26 years old, but make sure you use 03/04 specs when doing so. I gotta say since I have done the alignment It feels so much better, way more predictable, and planted to the road. I think it’s also to note I have lowered suspension, front strut brace, huge front sway bar, and full subframe connectors.

 

[FoxMustangLvr]

I have 18x9 45mm offset Saleen wheels for a 10-15 mustang. Running a 245/40r18 tire?? I think, I need to double check that.

Normally the 18x9 have only 30mm offset but I bought a 10” wide rim that has 45mm off set and cut it down to 9” so it would fit.

I might measure the inside of the wheel in comparison to the wheel well and see if I can remove some of the hub face. Try to get the wheel to sit further inside.

The math does not work out with the wheel offset IMO. 10" wheel +45mm narrowed 25.4mm is now a 9" wide wheel with about +20mm offset. The outer lip of the wheel still sticks out too far in relation to the hub face. The ideal offset for an IRS Fox is 9" wide +45mm and you should be able to tuck a 275 tire with no issues. I have 18x9 +35mm with a 245 tire out back with no rubbing but I had to camber my wheels to make it work.

 

[90sickfox]

That's a sweet idea...narrowing the 10 inch wheel.

245/40 18 should fit....I run the same size on 2012 18s. I also have 265/40s that do work but are a little close on the inside.

Wish they would've built these cars to tighter tolerances. Half inch differences from quarter to quarter aren't uncommon.

 

[sab24711]

That's a sweet idea...narrowing the 10 inch wheel.

245/40 18 should fit....I run the same size on 2012 18s. I also have 265/40s that do work but are a little close on the inside.

Wish they would've built these cars to tighter tolerances. Half inch differences from quarter to quarter aren't uncommon.

The price of doing so sucks but I really wanted that style rims, so had to pay up. The only other problem is I would like to have a spare tire so I need to cough up the money for another rim or find another rim that fits. Btw his website rocks rimsntires.com

 

[sab24711]

The math does not work out with the wheel offset IMO. 10" wheel +45mm narrowed 25.4mm is now a 9" wide wheel with about +20mm offset. The outer lip of the wheel still sticks out too far in relation to the hub face. The ideal offset for an IRS Fox is 9" wide +45mm and you should be able to tuck a 275 tire with no issues. I have 18x9 +35mm with a 245 tire out back with no rubbing but I had to camber my wheels to make it work.

I’m not to sure about that. 20 mm off set would not fit like it currently does. taking a 10” rim and cutting the barrel of the rim 1/2 difference will only change the backspacing of the rim. The Center of the rim to the face of the mounting surface will still hold +45mm mm. If I were to cut from the Center and remove 1/2” towards the face of the rim it will change both the backspacing and the offset.

If you go to this website rimsntires.com
which is awesome. you can scroll down to the bottom and where it says more click the size calculator. Cool site to find rims from other models that have the specs your looking to run.

 

[FoxMustangLvr]

I’m not to sure about that. 20 mm off set would not fit like it currently does. taking a 10” rim and cutting the barrel of the rim 1/2 difference will only change the backspacing of the rim. The Center of the rim to the face of the mounting surface will still hold +45mm mm. If I were to cut from the Center and remove 1/2” towards the face of the rim it will change both the backspacing and the offset.

If you go to this website rimsntires.com
which is awesome. you can scroll down to the bottom and where it says more click the size calculator. Cool site to find rims from other models that have the specs your looking to run.

True, I got that wrong. Can you post a pic of your car with these wheels?

 

[sab24711]

True, I got that wrong. Can you post a pic of your car with these wheels?

^so this is the side that has given me problems. i think im just gonna crank that camber bolt untill she clears.^

 

[FoxMustangLvr]

@sab24711
Very nice!! I would start by measuring the back space of each rear wheel to make sure they are the same. Second, I'd check to make sure your IRS is centered under your car. Your passenger side wheel does look too far out IMO.

 

[90sickfox]

Those wheels do stick out a little further than I'm accustomed to. Reminds me of when I first started doing the IRS swaps.

The biggest issue I've had is being able to fit a decent width tire. The interference is always on the inside for me. If I do a hard tail conversion I'll detail it in my build thread.

 

[Mustang5L5]

How much resistance did you get convincing tech to go by specs for the 04 cobra?

I remember wgen I asked around for custom specs to be done on my car getting total refusal from all shops, which prompted me to DIY.

 

[sab24711]

How much resistance did you get convincing tech to go by specs for the 04 cobra?

I remember wgen I asked around for custom specs to be done on my car getting total refusal from all shops, which prompted me to DIY.

well i tired one shop and after explaining, what felt like forever, what i wanted done they refused to help. so i talked to a buddy of mine that works at a dealer, he told me no problem so we both aligned the car together. we need to ask the mechanic there to help set up the machine. they all looked at us like you know this car isnt an 04 cobra right....

@sab24711
Very nice!! I would start by measuring the back space of each rear wheel to make sure they are the same. Second, I'd check to make sure your IRS is centered under your car. Your passenger side wheel does look too far out IMO.

how do you center the irs? i didn't think it was possible to do so. i guess it has to do with the sub frame of the irs? im confused becasue the irs front sub frame gets mounted to the old lower control arms and the rear get mounted on the frame with with brackets. where does the left to right movement come from? i did take measurement but that was from front to back, to make sure the rear brackets were both in the same place.
i completely agree that the wheel sits further out on the passenger side. if i cant center the rear you think its safe to remove 5mm from the hub face of the wheel to pull rim towards the inside?

Those wheels do stick out a little further than I'm accustomed to. Reminds me of when I first started doing the IRS swaps.

The biggest issue I've had is being able to fit a decent width tire. The interference is always on the inside for me. If I do a hard tail conversion I'll detail it in my build thread.

Ive considered doing the hardtail mount but after measuring and checking over and over again i was convinced i could get away with my current setup. i am looking forward to seeing you try this, im interested what the gains could be. im happy at 9" but more it always better.

 

[90sickfox]

The hard tail conversion should let a 10 inch wheel fit the rear with a little beating of the wheel tub.

Its very hard not to have an IRS centered. The brackets bolt to the side of the rear frame rails. If the rear frame rails are off then the rear will be off.

In my experience the difference comes from the frame rails being welded in by ford a little off....or the quarters being a little off.

Something else that affects how far the wheels stick out is the ride height. The IRS rear actually pushes the whole wheel out as the suspension compresses. When measuring my track width, with the wheels on and springs off, I noticed the tires moved out. Camber comes back in a little when fully compressed.

My drivers side is a tad closer to the wheel arch with 50mm 18in wheels and an 8mm spacer. My quarters aren't rolled....but I have no rubbing. I'm also using stock cobra springs. This is on an '88 notch.

 

[90sickfox]