Talk to me about coupes with 15" wheels

[JohnK]

I'm in the very early stages of contemplating a next build, and top of the list at the moment is a coupe build. I'm picturing a period-correct(ish) look with 15" wheels, 427W with an Inglese EFI stack and turkey pan, etc.

There will, of course, be some modern elements like IRS, T56 trans, Motec traction control, Bosch motorsport ABS, air conditioning...

I have many, many questions (!!). Here are just a few of them.

- When I search online for photos of coupes with 15" wheels, every single photo I've found has Trigo FIA pin-drive wheels, which tells me that they're not gen 3 coupes. Has anyone here built a gen 3 coupe with 15" wheels? If so, please share photos!

- There is a particular stance/look that I have in my mind that I want to achieve that mimics the original Daytona coupes, like this. What would be the best tire sizes to achieve this? I'm guessing a 295 in the rear is too big. Are 275's the way to go?



- I know that the conventional wisdom is that pin drive is not possible on the gen 3 coupe with IRS. "If money were no object" (not saying this is the case, but hypothetically speaking), how would one go about putting 15" Trigo FIA pin drive wheels on a gen 3 coupe with IRS? On the front, would custom spindles be an option? Or can I simply account for the 3/8" pin drive adapter by going with a slightly narrower tire (225 vs 245)? This would be in keeping with the overall look in the photo. On the rear, it looks like I might be able to simply machine 3/8" off the Mustang spindles where the hub bolts on, to account for the thickness of the pin drive adapter, and then have custom shorter half shafts made? Or can I simply go with 275's on the car and not worry about the added 3/8" of the pin drive adapter?

Thanks!

[JohnK]

...and just for fun, here's the inspiration. All 6 of them!

[Jeff Kleiner]

Many with IRS on a Gen3 wind up going with a 1 inch or thicker spacer to move the tire and wheel outward since the standard FFR configuration has the tucked in pretty far. For this reason I don't think the thickness of a pin drive adapter will be an issue. I assume that you are aware that the standard 2015 and up 13" rotors don't fit inside of a 15" rim however FFR has an option to use 11.65" rear brakes. I can't imagine that a 295/50-15 will cause an issue. I saw a Gen3 that had pin drive in front with donor Mustang spindles and the geometry was a disaster! I think it could be accommodated with the FFR spindles but it will probably require offsets that will preclude showing much dish to the wheel due to the thickness of the adapter. Plan "B" might be to use the #12508 pin drive width lower control arms in conjunction with short sleeves in the UCAs to bring the spindles in both top and bottom. That would also require shorter tie rods/ends for the rack.

Good luck!

Jeff

[JohnK]

Thanks Jeff!

- Yes, my plan at the moment would be to use Gordon Levy's Wilwood package for 15" wheels.

- That's great to hear about the rear fitting 295's even with the pin drive adapter.

- On the front, in theory a custom offset could work. I haven't called Vintage Wheels but their website says that the 15" FIA wheels are one-piece cast wheels so offset options are limited. Not sure if they have an offset that would work. I did see the photo you've previously posted of the front suspension with Mustang donor spindles and I agree that this is a disaster. Definitely don't want to go that route. Pin drive width lower control arms with shorter sleeves in the upper control arms could be an interesting option.

I appreciate the input.

-John

[drewr]

I’ve got a coupe with 15” wheels and a 3 link. I have 1” spacers on the back. I have Mikey Thompson Sportsman S/Ts 235/60R15 on front, 295/50R15 on back. IMG_2766.jpgIMG_2752.jpg

[JohnK]

Thanks for that! What's your ride height set at in those photos?

[drewr]

About 4" in front, 4.5" in back. I have a sloped driveway and didn't want to worry about scraping with all the in and out while I was driving it for shake-downs and licensing. I'm doing body work now so the stance may change a little as I"m getting it dialed in.

[JohnK]

I've been poking at this a bit more over the last day, and thought I'd post some additional information I've found to this thread. To my original question: "how would one go about putting 15" Trigo FIA pin drive wheels on a gen 3 coupe with IRS?" It seems that the answer is that you can't. The main reason for that is that the FIA wheels are one-piece cast wheels that are only offered in a backspace of 3.7". If I assume that the FFR 15" wheels are a "known good" fit on the coupe, and those specs are:

Front: 15x8; 5" backspace (+12.7mm offset)
Rear: 15x9; 5.48" backspace (+12.19mm offset)

When I compare this to the FIA wheels, which are 15x7.5 and 15x9.5 with 3.7" backspace, I get:



This shows the FIA wheels sticking out 21mm further in the front and 57mm further in the rear, not taking into account the 3/8" thick pin drive adapters. With adapters, that's 2-5/8" additional protrusion in the rear, per side. That might be doable with a narrowed solid axle, but not feasible in any sort of practical way with an IRS.

BUT...

Vintage wheels also carry a Halibrand style wheel that's a 2-piece wheel and can be custom built to different backspace/offset specs. I could, in theory, go with a rear that's built to the FFR specs (15x9, 5.5" BS) and with the 3/8" pin drive adapter it would stick out 3/8" further than the FFR wheels. As Jeff mentioned, lots of folks run spacers to bring the wheels further out on the coupe, so that would work fine. On the front, I would need a 15x8 wheel with 3/8" more BS than the FFR spec, and it would bolt right up without any changes required to the standard width front suspension. The only consideration there is what would that front wheel look like with that much backspace.