28" Tall Tire

[gtrclark]

I checked the https://thefactoryfiveforum.com/show...ire-Repository and it doesn't look a single person is running a 28" tall tire.

Are there clearance issues, or are the 26" tall tires just the norm?

Pretty sure the car here is on a 315/40 rear (27.9" tall) and to me the fit looks amazing: https://stanceworks.com/2019/03/aest...lass-champion/

[Blueblood]

I have 27.3” rear tires and they are very close the one of the braces behind the seat. 28 inch tall tires may fit with some clearance modifications. My tires are also only 9.3” wide so a wide tall tire will definitely require some cutting and welding.

[Logan]

You may be aware, but the design of the Gen3 Coupe chassis tubing that forms the rear wall of the cockpit, particularly the short angled 1" square tube behind the seats, is poorly designed from a tire fitment perspective.

I'm sure the Finite Elemental Analysis (FEA) determined that to be a great location for that tube to increase overall rigidity, which I am all for, but for a racecar it is simply in the way of fitting large tires. Due to the how the tube is angled in 3D space, the tire fitment is more of dynamic puzzle to solve. For example, you can run a tall tire if you want but it will have to be pretty narrow and spaced/pushed out to be flush with the fender in order to have clearance to the chassis. Alternatively you can run a wide tire if you want to, but it needs to be shorter in height/smaller diameter, and also spaced out as far as possible in order to clear the chassis. A tall and wide tire such as a 28" drag racing slick would just not fit without modifying the chassis. Speaking of which, I have notched the offending tubes on my Coupe-R (pictures in my build thread), but know that this is only marginally better than cutting the tubes out entirely as it from a strength perspective. Other builders have modified their tubes in similar ways seeking better tire clearance.

Ride height plays a crucial role here too, since the relationship of geometry in this area means that as you increase ride height, the distance to the tube increases at a different rate. To fit the largest tires, higher rear ride height is better, but measuring your own car is the only way to be 100% confident in your specific setup. If you're pushing the limits running super close clearances like myself and some other folks, remember to take into account the lateral tire deflection, speed-induced diameter increase, suspension settings at full compression, bump stops, etc. You can run with your tire 1/16" from the tube under all those conditions, but it takes a lot of measuring to figure those out.

PS. I wrote the repository, and I added as many peoples setups as I saw data posted for, but it is by no means comprehensive. There could be people out there running 28" tires that aren't on the forums, or FB groups, that I have no way of contacting. So while it may be a limited data set, it is still very helpful since the vast majority seem to be running 25.5-26.5" tires anyway.