Wheel Fitment…One More Time

[GT53]

Hey All….Here we go again with the “What Wheels Will Fit” discussion.

I know this topic has been out there for quite some time, but in researching “aftermarket” wheels and tires for the Roadster I’m more confused than ever. I opted NOT to go with the FF Halibrands. Nothing against them but I want something a bit different. I spoke with a few of the manufacturers that have been mentioned on this forum and was told generally that they don’t know if a specific wheel will fit, or what modifications might be necessary to make them fit, which doesn’t help me at all.

I have the spec sheet from FF in front of me so I am aware of what “The Book” says regarding wheel specs but questions remain.

I opted for the Wilwood brake kits front and rear on an IRS and I am planning on 18” x 9’s on the front and 18” x 11’s on the rear. (Tire options as well???)
So my questions are these: With regard to offset, are the numbers (24mm front, 12mm rear) a hard number or is there a range that will work? And, the same question regarding backspace. Is 6.00” / 6.46” a hard number for front and rear?

In short I have found a few options that come close to the “spec” numbers but virtually nothing that meets ALL of the numbers, so before I shell out the dough I’d like to get “educated” as best I can.

If any of you that have a MK IV with IRS and Wilwoods can shed some light into the dark recesses of my tiny little brain I would certainly appreciate it.

Much obliged in advance for all the wisdom on this forum.

Greg

[Hoooper]

The answer depends on your tire choices. For example, I am running the FFR specs on my wheels, with 275/35R18 up front and 315/30R18 out back with IRS. In the front, the tire rubs the F panel slightly on full lock and just barely clears the fender. Out back, the tire just touches the coil spring on full droop and just barely misses the body under compression. If you run wide tire options youre pretty limited. If you go for skinnier tires, shorter tires, or tires that arent as square as my R888Rs (which I dont think are all that square) you would have slightly more flexibility.

[BradCraig]

I don't have all the answers, but I will say that the FF 18" backspace and offsets work really well as far as fitment in the wheel wells\brake clearance\etc and I would not stray too far from those specs. There are a lot of folks on here (and builders) that can likely give you input as to what works. May want to also post in the Builder group on FB.

[CaptB]

For those situations that the tire rubs, does the FF Metal "Fat" F panels help?

I'm running 15" wheels so my Wilwoods are smaller than what can be ran in the bigger wheels but I didn't know if the "Fat" F panels would help out here.

https://www.ffmetal.com/FatTireFpanels.html

[JohnK]

I have 245/40R18's on the front (on FFR wheels) and with the FF Metal Fat F panels I was able to remove all steering rack limiters and still have enough clearance that the tires don't rub at all.

https://thefactoryfiveforum.com/attachment.php?attachmentid=107367&d=1558050124

[CraigS]

I can't think in offsets but I can think in back space-BS. I agree w/ BradCraig that the FFR specs are close to absolutes. You can run more BS but you may need to install a wheel spacer. At the front don't worry about hitting the aluminum panel. It would make a mark on the panel but do no damage to the tire since it is hitting a flat surface and it happens at parking lot speeds. At the front hitting the fender flare in front of the tire as the steering is turned to full lock is the more common problem if the tire/wheel doesn't have enough BS. Overall I would stay within 1/4 inch of the FFR specs. Look at these;
https://www.americanmuscle.com/buwh1-9404.html
and these
https://www.americanmuscle.com/dedibuwh.html
These are 17s that I happened to save links for. You can find 18s also and if you match the BS specs you will be fine. There are many different styles and colors of wheels that fit. And they are relatively inexpensive since they fit Mustangs.