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Discussion Starter · #1 ·
Just purchased a 1990 LX convertible and need some help as far as backspacing and rim size. It has a five lug conversion and not sure if the backspacing will be different compared to a standard 4 lug.

Does the backspacing change when converting to 5 lug?
If so, can it be different depending on where the axels are from?

If it is all the same, what is the recommended backspacing for running a 275-40-17 on a 17x9 rim?

Thanks in advance for the help.
 

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Just purchased a 1990 LX convertible and need some help as far as backspacing and rim size. It has a five lug conversion and not sure if the backspacing will be different compared to a standard 4 lug.

Does the backspacing change when converting to 5 lug?
If so, can it be different depending on where the axels are from?
In most cases, the backspacing / offset required up front does not change with a 5-lug conversion. As SNK VNM said, the 5.95" BS / +24mm offset (as used on the original '95 Cobra R wheels) works. I've also seen folks use the 6.12" BS / +28.5mm offset of the later Ford wheels ('03/04 Cobra, FR500, 10th Ann).

However, the requirement in the rear does change depending on what axles were used. You need to find out if it still has Fox length axles, or if they used '94-98 SN95 length axles (which are 0.75" longer on each side).


+24 offset, 5.95 back spacing is very common for a 17X9
Thanks for the reply, would 25mm offset and 6" back space work also?
A 1mm change is not going to make any difference, so yes, a +25mm offset or 6" BS will work.
 

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Discussion Starter · #5 ·
he 6.12" BS / +28.5mm offset of the later Ford wheels ('03/04 Cobra, FR500, 10th Ann).

However, the requirement in the rear does change depending on what axles were used. You need to find out if it still has Fox length axles, or if they used '94-98 SN95 length axles (which are 0.75" longer on each side).
So I guess my question now is how do I determine the axels that were used? Unfortunately the owner prior to the one I purchased the car from did the conversion and he didn't know himself.

The car does have disc brakes if that helps
 

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So I guess my question now is how do I determine the axels that were used? Unfortunately the owner prior to the one I purchased the car from did the conversion and he didn't know himself.

The car does have disc brakes if that helps
What Patrick Olsen said is spot on. Aside from actual measurements of the axle, I'm not sure how to identify them. Some aftermarket axles will have a sticker in the hub, under where the center cap would cover. Sn95 axles might have an abs ring on them depending on several factors.

What wheels are on it now?
 

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Discussion Starter · #7 · (Edited)
What Patrick Olsen said is spot on. Aside from actual measurements of the axle, I'm not sure how to identify them. Some aftermarket axles will have a sticker in the hub, under where the center cap would cover. Sn95 axles might have an abs ring on them depending on several factors.

What wheels are on it now?
See below, nothing on the end of the axel, maybe you can I.D. the rims, any idea? The previous owner didn't know many specifics about the car :-(

Wheel Automotive lighting Automotive tire Sink Motor vehicle
Wheel Tire Car Automotive tire Vehicle
 

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See below, nothing on the end of the axel, maybe you can I.D. the rims, any idea? The previous owner didn't know many specifics about the car :-(

View attachment 1080432 View attachment 1080433
The wheels appear to be an aftermarket version of the 03/04 cobra wheel, in a deep dish version. They likely are 17X10 or 10.5. I suppose you could remove one, check for markings on the back side of the spokes and figure out exactly what size,offset, and back spacing they are, as that info is usually there. With that info, a little research on how to fit those specs on a fox would likely reveal what axles you would have to have to run those wheels.

That being said, if I had to bet, I'd bet you have fox length axles, solely based on those wheels.
 

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That’s an SN95 cobra disk brake setup.

poke your head around the backside and look at the axle brackets where the caliper bolts to the axle. The oem ones will be straight and have a rough cast+machined look to them. Aftermarket ones are steel with an offset that is usually applied via a brake.

edit: see below
 

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Discussion Starter · #11 ·
The wheels appear to be an aftermarket version of the 03/04 cobra wheel, in a deep dish version. They likely are 17X10 or 10.5. I suppose you could remove one, check for markings on the back side of the spokes and figure out exactly what size,offset, and back spacing they are, as that info is usually there. With that info, a little research on how to fit those specs on a fox would likely reveal what axles you would have to have to run those wheels.

That being said, if I had to bet, I'd bet you have fox length axles, solely based on those wheels.
Part of the problem is I feel the offset on the current rims is not correct for the car, even with a narrower tire, the lip of the rim seems to be out as far as the fender lip, so I don't think finding out the current specs is going to help
 

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Discussion Starter · #12 ·

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What do you think these are?
View attachment 1080438

Looks like OEM brackets to me but if you could take a wider angle shot looking in to the axle tube like mine it would give us a better angle on where we need to see.


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Yup. Much clearer.

Same setup as me. Oem Ford brackets and likely 94-98 SN95 axles.

That means each wheel is pushed out an additional 0.75” each side over fox offset. That might be the main contributing factor to why you feel each wheel is out too far in the rear.

Your options are to find a wheel with a much deeper offset/BS or to modify your disk brake setup using the offset brackets I listed a few pages up and a set of axles like these




While changing the axles/brackets is more money, it will make more wheels available to you.


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Discussion Starter · #16 ·
Yup. Much clearer.

Same setup as me. Oem Ford brackets and likely 94-98 SN95 axles.

That means each wheel is pushed out an additional 0.75” each side over fox offset. That might be the main contributing factor to why you feel each wheel is out too far in the rear.

Your options are to find a wheel with a much deeper offset/BS or to modify your disk brake setup using the offset brackets I listed a few pages up and a set of axles like these




While changing the axles/brackets is more money, it will make more wheels available to you.


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Thanks so much Mike, that explains a lot.

So if I went the wheel route, what would the back space need to be in order to properly tuck a 275-40-17 tire?
 

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Check out this thread. Pretty much the same subject being discussed

17x9 wheel sets for SN95 rear axles


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Discussion Starter · #18 ·
Check out this thread. Pretty much the same subject being discussed

17x9 wheel sets for SN95 rear axles


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Love this forum. Thanks again for your help! 🍻
 

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Discussion Starter · #20 ·
Yup. Much clearer.

Same setup as me. Oem Ford brackets and likely 94-98 SN95 axles.

That means each wheel is pushed out an additional 0.75” each side over fox offset. That might be the main contributing factor to why you feel each wheel is out too far in the rear.

Your options are to find a wheel with a much deeper offset/BS or to modify your disk brake setup using the offset brackets I listed a few pages up and a set of axles like these




While changing the axles/brackets is more money, it will make more wheels available to you.


Sent from my iPhone using Tapatalk
I now see what you are talking about as far as limited wheel options. So if I switch offset brackets and axles, I can just use the standard fox body OF/BS then (what SNK VNM originally posted)?
 
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