Ford Shelby GT500 Forum banner
Status
Not open for further replies.

Rear Wheel Fitment

2007 - 2014 
4K views 12 replies 5 participants last post by  Robert M 
#1 ·
Figured I'd start another thread on the subject since I realized I am still rubbing in the rear last night and I'm in search of the perfect offset before I order new wheels. I think my issue may have more to do with my ride height than anything else as I am lower than most on coil-overs. Anyways, on to the details.

Tires: MPSS 315/35/20 The rim protector sticks out about 2mm past the fender, but the tread will tuck inside.
Wheels: 20x11ET59
Suspension: Cortex Watts Link, Steeda Coilovers 250lb front and 200lb rear springs mounted on the axle (did not remove rear shock covers, have a tiny bit of space at full droop)
Mods: Bumpstop relocation with shorter bumpstops that I'm basically sitting on. The only thing I don't like about this mod is the thickness of the plate takes away suspension travel.

Thought the Watts made this go away and I think it has in normal driving, but apparently not when going up a steep drive which I had to do yesterday (incredibly rare in Florida). So now I want to call out everyone I know with a more aggressive setup than me.
@pureshot is running 20x12ET57 with 335/30/20 out back. This puts the inside of your wheel almost 11mm closer to the frame than mine and you have wider tires. If you're not rubbing, can you tell me a little about your suspension? I know you stick out a little past the fenders, no issues bottoming out?
@Catmonkey just changed to 20x11.5ET63 with 325/30/20 MPSC2 out back. The inside on your wheel is a little over 10mm closer to the frame than mine and you also have wider tires. I know you are running 250lb springs in the rear and haven't really tested the setup yet, so anxiously waiting. I also think you removed your fender liners?
@Carsten89 just widened Alcoas to 20x12ET62 with 325/30/20 R888R out back. The inside of your wheel is over 15mm closer to the frame than mine and you also have wider tires. Know you haven't had a chance to test yet, but anxiously waiting.
 
See less See more
#2 · (Edited)
Just a few photos to help visualize.

In the rubbing photo, you can see some text off the tire, so it is worst right around the rim protector on the lower part of the tire.

Starting to lean back to just doing the R888R 305/35/20 and not fighting for the MPSC2 325/30/20.
 

Attachments

#10 ·
I've got the same 1/16" tire bulge beyond the fender lip as you have shown above, that is with 12" Alcoa's and 325/30 Dunlops......



Over the years, since I did my Alcoa widening project (about 6 years ago, maybe a little longer), I found that others, even with 315's were having contact/rubbing issues. There was one specific owner who built out an exact duplicate of Alcoa's, just like mine with the same exact tires for his 2008 and could not get them to fit without contact, he backed off to 315's and still could not get them to work without spacers. We finally came to the conclusion that these cars are not all jigged the same when the body is welded together and some cars have more inward space in the rear fender area, and some have less........

I also have coilovers, Eibach Pro Street-S.

R
 
#3 ·
@Catmonkey, I know I saw in an old thread you laid the 325 and 315 down and put a level across on 11" wide wheels they were the same. Any chance you measured the overall width on the 11.5 wide wheels?
 
#12 ·
No, I didn't. Michelin's specs on the PSC2 for the 325/30 showed a 13" width as measured on an 11.5" wide rim, so I didn't look for confirmation of that fact. If I need to take the rear tires off this weekend for some reason, I'll see what I come up with. But from what I know, that measurement seems reasonable. Since Michelin measures their 295/35-20 on an 11" rim, I did verify that their measurement agreed with mine.

I read this statement on Tire Rack: "The industry rule of thumb is that for every 1/2" change in rim width, the tire's section width will correspondingly change by approximately 2/10"." That's probably true of many 50 to 75 aspect ratios, where you don't have a short sidewall. While it may not be 1 for 1 on a 30 or 35 aspect ratio, it's going to be fairly close. If the rim protector is the widest point of the mounted tire, then it probably will be 1 to 1.
 
#4 ·
Have you tried a rear spacer? Looks like you have room to push out the rear tire some more. Comparing your’s to my old setup that didn’t rub, looks like a spacer would solve your problem.






Sent from my iPhone using Tapatalk
 
#5 ·
Just a thought. Aren't the 315/35/20 pilot SS at 28.7 O.D.?
That is a full inch taller than the 325/30/20 Cup 2's at 27.7 O.D.. I remember @Catmonkey saying he thought the extra height he had on some old 315's may have increased the rubbing. So if you switch to a 325/30/20 at 27.7 O.D. that may make the difference in not rubbing.
I'm sure the experts can chime in and give more info. on this.
 
#6 ·
I'm fully expected some amount of rub on off-camber inclines. I just don't take these fast. It will rub the paint off the inner fender, but I don't see any wear on the tire with my 315s. I just don't think you can avoid some amount of the rear axle twisting and the tire making contact in those extreme situations. You can only go up so much on spring rates before it will be like driving a cement truck. And I agree with Carsten's comment. I think you could go outboard about 1/4" if you have that much clearance on both sides. But then I see another photo and the clearance looks much closer. I think if you wanted to prevent rubbing, you'd need to stay with about a 305 and get it fairly close to the outer fender for inside clearance.
 
#7 ·
Thanks guys, yes, a couple mm spacer would fix it, but I'll be ordering new wheels, so just trying to dial in the offsets. As for the tire height, I definitely think shrinking the overall height will help some and I might need to raise my rear ride height a little, just trying to get an idea of where everyone is at and if they are rubbing. It's not something you feel, but you'll definitely see the marks if you jack the car up.
 
#8 ·
Cat, I figure the tread on the 325 will bring me out just under 1/4" at the top of the tire. I guess I just need to decide if I care about rubbing a bit or want to give up on the MPSC2s until they make some more sizes. Once @Carsten89 gives a road noise report, it may make my decision easier. That said, I've had these tires on for 6 years now with no damage to the inside sidewall of the tire, so maybe I'm just over thinking it.
 
#9 ·
Once @Carsten89 gives a road noise report, it may make my decision easier.

I should be able to take the car out tomorrow, I’ll probably post in my Alcoa thread but I’ll tag you in it so you’re notified.



Sent from my iPhone using Tapatalk
 
#11 ·
Thanks @Robert M, definitely followed your threads over the years too. Interesting point on the factory jig possibility. With your 12" Alcoas did you end up with the 62/63mm offset like most?
 
#13 · (Edited)
I don't know what the offset is/was, it is the original 9" Alcoa offset and then 3" added to the inside for 12". It was all trial and error with me, no one else had done much widening at that time, and instead were buying "other" wheels with their desired offsets. I did mine in a time when people were just starting to mention Eric Vaughn, in fact when I had my wheels widened, I had never heard of Eric Vaughn and had Weld Craft do my original Alcoa widening, it was that long ago. It may have been 8 years ago when I did that widening project.....time flies!

This was also a time when the Super Snake owner world was swearing up and down that the 10" Alcoa's "WOULD NOT" fit the front...........until I did it and posted pictures to prove it with fitment and lock to lock turning..........the rest is history.

R
 
Status
Not open for further replies.
You have insufficient privileges to reply here.
Top