335 30r18 wheel back spacing on gen 3 coupe

[Rsnake]

My coupe should arrive mid December and trying to get some wheel ordered as I know forgestar wheels can take a long time to receive. Looking at the f14 and trying to figure out back spacing to run a 335 30r18 in the rear on 12"wheels and 275 on 10" wheels in the front. I don't want to run a spacer and hoping someone has run this combo. Thanks

[Logan]

I have been working on wheel setups for quite some time. Forgestar, Rotiform, Rota, Rays/Volk, etc. The minimum offset on the wide Forgestar Super Deep Concave (SDC) wheels is +6 mm. I am currently thinking 11” front and 12” or 13” rear wheels. Don’t have my body on for measurement yet, just working with the inboard clearances for now. Here is some of the data I have collected over the past year or two.

FFR Snap-On/Logano Coupe Forgestars:
Front: F14 DC 18x10+6 (planned for 11” wide but hit deadline for filming)
Rear: F14 SDC 18x12+6 w/40mm spacer, effectively -34 offset

FFR Snap-On/Logano Coupe-R Volk ZE40:
Front: ZE40 18x11+15, Toyo R888 295/30R18
Rear: ZE40 18x11+15 w/25mm spacer. Toyo R888 335/30R18

FFR Coupe generic street/track fitment:
Front: Halibrand 18x11+12. Toyo R888 315/30R18, near limit for front tire size
Rear: Halibrand 18x11+12 w/20mm spacer, effectively -8 offset. Toyo R888 335/30R18

Forcefed1 Coupe; forum member:
Front: F14 DC 18x10+30. Toyo R888
Rear: F14 SDC 19x12+6. Toyo R888 335/30R19. Without spacer, tire rubs frame under even light loads.

Surfdog57 Coupe-R street setup; forum member:
Front: Halibrand 18x9+24. Toyo R888R 275/35R18
Rear: Halibrand 18x11+12 w/2” (50.8mm) spacer. Toyo R888R 315/30R18

Surfdog57 Coupe-R track setup; forum member:
Front: Advan RSDF 18x10+15. Tire size 275
Rear: Advan RSDF 18x11+15. Without spacer, tire rubs frame

[Rsnake]

Thank you Logan! I wil let you blaze the trail and figure out what's needed. I am planning on 335's in the rear and I am assuming you are also. I just don't like the idea of spacers, why add another failure point.

[Logan]

Between some racing friends and I, we have ordered enough custom wheels by now to have developed a spreadsheet to work with fitment data...lol. Typically, I try to work out the inboard clearance first, to fit as much wheel/tire as possible to the inside. Then see how much room is left to the outside/fender, and fill that too. This is all relative to the wheel-to-hub mounting surface, and involves highly precise measurements on offset/backspacing, the use of spacers, wheel deflection under load moving relative to the chassis and suspension, tire deflection relative to the wheel, shock travel arc location, etc. Using spherical bearings in place of rubber or polyurethane bushings means I can get even tighter tolerances since I don't have to leave excess room for components to flex within their mounts.

I prefer to press extended wheel studs into the hub, and use slip-on spacers which become clamped between the wheel and hub with the lug nuts, as opposed to a bolt-on spacer which has its own set of lug nuts to bolt to the hub, then a second set of lug nuts and studs in it to bolt the wheel on. No foul experience with that type, but they're another point of failure, as you've said. And many believe not up to the abuse (bending moment from lateral loading) of racing. However, if you need more than 25-30 mm of spacer to get the fitment needed, bolt-on is typically the only option.

I'm actually trying to get the maximum wheel size possible for a set of racing wheels, like 11" with 315 up front, and 12" with 345 rear. Then I'll get a second set for street use. Something like 10" 275 front and 11" 315 rear.

[Rsnake]

Logan,
Blaze the trail and let me know what you come up with. I appreciate it.

[Papa]

I just stumbled across this old thread and would like to see if anyone has any updates on the best wheel size for the Gen 3 Coupe that would let me run a wider wheel vs using a wheel spacer.

Using FFR's 18" wheel specs as a starting point:

- Wheel width = 11"
- Offset (ET) +12mm
- Backspacing = 6.46"

I think I can fit a 12" wheel with 0 offset (6.5" backspace) and have the wheel sit at the same place on the inner surface while pushing it out an inch toward the fender edge.

https://thefactoryfiveforum.com/attachment.php?attachmentid=213312&d=1746287108

Has anyone done this?

[JimStone]

Check out the Coupe Wheel Repository if you haven't already

https://thefactoryfiveforum.com/showthread.php?41600-The-Daytona-Wheel-and-Tire-Repository

[dsjrocha]

Also, don’t forget to consider the rear end setup. It’s still a toss-up between IRS and the 8.8 and whos running what setup. I’m not sure if the flanges sit in roughly the same location for all three variables. With the 8.8, you also have to factor in SN95 vs. Fox-length housings, which differ by about 1.5 inches flange to flange, SN95 being wider.

I just ordered a set of custom wheels for my Gen 3. Got the fronts mounted yesterday and they fit great. I'm still waiting on the rear tires to arrive so I can fit the rear, it's looking pretty tight, so we’ll see if there’s any rubbing.

For reference, I ordered:

Front: 19x9 ET +5

Rear: 19x11 ET -10

[Rsnake]

I am running 335 30r18 with 18x12 5.75" BS on the rear and 275 35r18 on 18x10 5.25" BS on the front.
The fit is about perfect except I did need to clearance the rear diag bar as the tire would rub. No more rubbing and looks great after some trimming
If I did it again, I would go with 315's as more tires are available and no issues out of the box. 19's look the best but if you are going to autocross and such I would go 18's.

[MSumners]

Just received my 19’ f14’s yesterday, used information here to hopefully run no spacer and minimize or eliminate rubbing but we shall see, will get them mounted up and post some pictures soon although it’ll be a bit longer to get the body on for a real eval.