IRS and 15" Wheels

[CobraboyDR]

Before Courtnie left she made it clear that neither pin drive wheels or 15" rims are compatible with the new IRS.

Can you guys explain specifically why this is so? I'm not challenging but want some edumacating on the subject.

And are there any reasonable workarounds?

Thanks so much!

[GoDadGo]

The IRS set up uses the Ford Mustang IRS Rear Knuckles from the 2015-thru-2017 model years and likely beyond.
The size of the brakes and size of the knuckle is was designed for 17-thru-20" wheels and only the base V6 wears the 17's.
Those parts simply don't fit inside a 15" wheel; however, Gordon Levy of Levy Racing may have a solution.
Hope this help and try reaching out to Mr. Levy because he is an expert on these cars.
You can see the parts at the site shown below:

https://www.americanmuscle.com/frpp-irs-knuckle-kit-1516.html

[edwardb]

As mentioned, the new Mustang brakes and Factory Five available Wilwood upgrades only fit 17-inch and up wheels. So a 15-inch wheel solution isn't available from Factory Five. But Gordon has developed Wilwood brakes that will fit, and I've seen at least one build completed with them. But pin drive won't be so simple. With the required pin drive adapters, the suspension track needs to be narrowed. That means shorter control arms, axles, etc. Plus whatever affect it might have on suspension geometry, chassis clearance, etc. Factory Five has not chosen to support this option. I suspect due to the low sales volume combined with the brake/wheel limitations. Due to the revised suspension and higher unsprung weight (plus rules issues in some cases) pin drive typically isn't desirable for competition either.

[CobraboyDR]

As mentioned, the new Mustang brakes and Factory Five available Wilwood upgrades only fit 17-inch and up wheels. So a 15-inch wheel solution isn't available from Factory Five. But Gordon has developed Wilwood brakes that will fit, and I've seen at least one build completed with them. But pin drive won't be so simple. With the required pin drive adapters, the suspension track needs to be narrowed. That means shorter control arms, axles, etc. Plus whatever affect it might have on suspension geometry, chassis clearance, etc. Factory Five has not chosen to support this option. I suspect due to the low sales volume combined with the brake/wheel limitations. Due to the revised suspension and higher unsprung weight (plus rules issues in some cases) pin drive typically isn't desirable for competition either.Thanks for the input.

Could not wheel backspace make up for the thickness of the adapter? Or am I missing something?

[CobraboyDR]

The IRS set up uses the Ford Mustang IRS Rear Knuckles from the 2015-thru-2017 model years and likely beyond.
The size of the brakes and size of the knuckle is was designed for 17-thru-20" wheels and only the base V6 wears the 17's.
Those parts simply don't fit inside a 15" wheel; however, Gordon Levy of Levy Racing may have a solution.
Hope this help and try reaching out to Mr. Levy because he is an expert on these cars.
You can see the parts at the site shown below:

https://www.americanmuscle.com/frpp-irs-knuckle-kit-1516.htmlThanks for the info, muchas gracias. I'll drop Mr. Levy a note.

[edwardb]

Could not wheel backspace make up for the thickness of the adapter? Or am I missing something?

I'm at the end of my knowledge on this subject. I don't know. I only know that historically for the FF pin drive option the suspension parts are different and FF chose to not offer them for the newer IRS setup. I understand the desire for authenticity, but IMO the 5-lug halibrand style wheels with the covers looks pretty OK and everything is pretty straightforward. These are 18's on the FF Anniversary Roadster prototype. Looks similar on the other wheel sizes.

http://i867.photobucket.com/albums/ab234/edwardb123/Factory%20Five%2020th%20Anniversary%20Mark%204%20R oadster/Misc%20Pics/IMG_3220_zpswkk3yjwi.jpg (http://s867.photobucket.com/user/edwardb123/media/Factory%20Five%2020th%20Anniversary%20Mark%204%20R oadster/Misc%20Pics/IMG_3220_zpswkk3yjwi.jpg.html)