Wide Body Wheel & Tire Specs.

[Ed07]

Ok, so I'll be installing a full CorteX suspension on my 2007 GT real soon—front SLA w/coil overs, sway bars etc, rear coil overs, watts, torque arm. . .

 

Once that is done, the next mod will be a Wide Body Kit for the rear. Which will probably happen next spring. Now, after talking with Flip over at CorteX, he says that with their rear coil overs—depending on the configuration—allow fitment of 11" wheels with an 8.25" backspace without issue. I know he prefers 18s for the handling characteristics but I plan on going with 19s or 20s for looks.

 

The Wide Body Kit says that the rear wheel specs will be a 13" wide wheel with 6.75" of backspacing. What I would like to know is if anyone with I wide body kit would be kind enough to measure the street-side clearance between the quarter panel lip and outward face of the tire.

 

How much room did the folks at Shelby allow? On my GT stocker with 235/55/17s the clearance seems to be about 0.6". Ideally, I'd like the tire to come right up to the quarter without any protrusion and about an 3/16" clearance.

 

Does anyone have offset/ET wheel specs for the 13" wheels (w/345/30/20s) that Shelby recommends?

 

I'm wondering just how wide a wheel/tire combo the wide body kit would [theoretically] allow.

[ageishecker]

Without measuring I can tell you there's not quite enough clearance. On suspension compression the lip touches the sidewall. Others have reported the same thing.

[Ed07]

That's why I'm asking. . .

 

It shouldn't be that difficult using a couple of straight-edge squares. Like I staid the stocker allows for 0.6" clearance, but that still doesn't tell the whole story.

 

On my stocker GT, the tire specs are as follows:

 

1. Tire size: 235/55-R17

2. Offset (ET) of between 32-42 mm. (Mine is 42 mm)

3. Rear Fender Gap (top of tire to rear quarter pane lip): between 2-5/16" [2.3125] and 2-3/8" [2.375] (or between 59 mm and 61 mm if you prefer)

 

4. The distance (i.e., the tangent line) relative to the tire face/sidewall occurs at roughly between 4-5/16" [4.3125] and 4-9/16" [4.5625] (or between 110 mm and 116 mm)

 

That tells me that on a bone-stock Mustang GT with similar specs, the rear suspension would need to compress a distance of at least 110 mm before rubbing on a tire that protruded more than 0.6" (give or take) from the factory rear quarter panel. The stock configuration would clear completely.

 

That brings us to the question of just how much rear suspension travel Ford provides the S197 before bottoming out. Does the suspension even cycle more than 3/3.5"? I'm inclined to believe that the CorteX suspension will mitigate a lot of this. The rear coil overs package really nicely, and allow for 8.25" of backspace on a factory axel housing.

 

As far as fitment with the CorteX my guess is that Filip is being conservative with the 8.25" backspace. It allows a rim of the following specs:

 

285/40-R18 on a 10.5" wide rim/wheel with an offset (ET) of: 63 mm

 

* Though I'm told (perhaps with some minor mods) a 305/30-R20 fits beautifully with an offset of: 62 mm

 

I'm wondering if the 8.25" is with the bump-stop still in place? Removing that will certainly provide even more clearance. And the coil overs used won't have the shock dust cover as on the stock GTs.

 

All that said, I'd still like to get some rough measurements from folks that actually have the wide body configuration.

 

Looking at some of the photos on this link indicate that there seems to be no issue with street-side rub, though the photos could be deceiving. Hopefully other will post-up some front-on shots or above shots with measurements etc.

Edited May 1, 2016 by Ed07

[Ed07]

Just figured I'd bump this topic to see if anyone can provide the measurements. I suppose I could email someone at Shelby America directly. Don't know if I'll get a reply though.

[ageishecker]

You may have a hard time finding anyone with a 2007 widebody. Any measurements from my 2013 are probably irrelevant.

[Ed07]

It's likely that the measurements for a 2013 are in fact irrelevant—unless its the same kit for all s197 models; in which case I would just be curious about the distance from the inner wheel well seam/partition to the outside fender lip. Like I said, I'll try and work out the maths using my 2007, as well as the backspacing distance Filip from CorteX provided. So if you happen to get some spare time, I'd greatly appreciate any data you might be able to provide

[ageishecker]

The kits are completely different. Look at photos of both and you'll see.

[Ed07]

You're right.

[Ed07]

So no one with a Wide Body kit for 2005 to 2009 Mustangs?

[HyperStangs]

I hate to throw a wrench in your plan, but adding the wide body kit to a CorteX suspension car is like putting lipstick on a bodybuilder. CorteX builds the absolute BEST suspension on the market, BAR NONE! But your entire suspension is based around the stock wheel offset, by moving the tires essentially out in one direction, as opposed to widening them both inboard and outboard, you're taking away virtually every positive aspect the CorteX suspension affords you. In fact, from a performance perspective, the wheel/tire setupon a wide body , keeping all other aspects of the car the same, is the WORST think you can do! It looks cool, I'll grant you. But cars that utilize wide body modifications START with extending the control arms, making room for inboard tire clearance, changing the wheel offsets to keep the pivot points centered in the wheel, and THEN develop body panels that accommodate the new modifications. You're looking at inboard bearing issues, scrub radius problems, less responsive steering, TONS of extra unsprung weight, just to name a few. I would venture to bet that a CorteX equipped car running 10's at all four corners would beat a CorteX equipped wide body car running Shelby wide body wheel specs all day long and twice on Sunday. BUT, if you rally want the wide body wheel specs, I not only have them I can get you the wheels... but I'd hate to do it.

[Ed07]

 

But your entire suspension is based around the stock wheel offset

 

Guys run wider wheel/tire combos all the time. I get a sense that you're misunderstanding a few things.

 

I am absolutely *not* going to be running stock wheels with stock offsets! And if you really think I'm going to be using some off-the-rack wheel with questionable offset, then you got it wrong.

 

 

 

But your entire suspension is based around the stock wheel offset, by moving the tires essentially out in one direction, as opposed to widening them both inboard and outboard, you're taking away virtually every positive aspect the CorteX suspension affords you.

 

​Well, I've already spoken to Filip and as I understand it, the offsets are going to change *anyway* if I go with a wider wheel. Apparently I can safely go 305's on a 11" wheel with 8.25" backspace with zero issues because of how the rear coil overs package, and that will work perfectly on the CorteX setup. I'm not going to just bolt in some unproven suspension, and then sit at home and chop up my quarter panels for the wide body kit. There's been plenty of planning. And if you're telling me that all else being equal, simply adding just the rear wide body kit to a car with a full CorteX suspension is going to have adverse effects, forgive me for being a little skeptical since the overall width gained in the rear is what, 3 inches per side?

 

​I know that Shelby sells rear wheels with the following specs:

 

20" wheels that are 10.5" wide with a 50 mm offset (7.7" backspace). Coupled with 295/30 tires and there's zero issue—and that's for stock/unmodified rear suspension.

 

The rear CorteX suspension allows for even MORE backspacing: 8.25". That' an additional half-inch (0.05") clearance, and that makes sense given that Filip said the Cortex suspension would allow for an 11" wheel. The trick is to estimate the offset of the 11" wheel while keeping the front face of the wheel+tire no more than 0.5" outward because that's about the limit the wheel can be pushed outward "sterrt-side" without rubbing issues. . . That tells me an 11" wheel with offset ranges of 48 mm (min) to 56 mm (max) will be just fine on the rear with CorteX setup. You could bump the tires up to 305s and still remain safe.

 

The only thing the wide body kit allows for is an increase in wheel width *outward*, and that street-side increase amounts to 3-inches per side. I'm guessing that we can figure that out as well.

 

The max tire is going to be 345, and the increase in wheel well space from the wide body kit will allow for a 13" wheel. If the wide body kit extends each rear quarter panel outward by 3 inches, a 20" wheel that's 13" wide running 345s will be safe with offsets between 15 mm (min) and 30 mm (max). Playing with wheel width even more, I suspect that (mathematically) you might even be able to squeeze 13.5" wheels underneath the rear once the wide body is installed. I'll play with the numbers more.

 

In the mean time, I'll contact Filip over at CorteX, and get his take.

Edited May 29, 2016 by Ed07

[Ed07]

UPDATE:

So if the wheels for the 2005-2009 wide body are recommended to be: 13” wide with a 6.75” backspace that means the offset is going to be between -7 mm and -8 mm

With potential (theoretical) offsets in the rear of: + 31 mm (using the CorteX coil overs) which will leave an additional 1.4” tuck easily clearing the street-side lip of the rear quarter panel, but would look like crap tucked way inward like that.

Same wheel and tire with a 0 (zero) offset would yield a 7” backspace (more than enough for the CorteX coil overs. and leave about a quarter inch (.25”) tuck to clear the street-side lip of the rear quarter. Which would probably be ideal and nearly identical backspace-frontspace with an offset of -14 mm on those wheels yielding equal frontspace-backspacel. The only problem is that the front face of the tire would protrude about a half inch outside the quarter and rub. so 1 -3 mm or -2 mm offset would probably be the absolute limit to avoid rub.

Other folks are welcome to check the maths. . .

Edited May 27, 2016 by Ed07

[HyperStangs]

I think you're misunderstanding actually. The wide body does NOT widen the wheel around the thrust line and the proper pivot point. Yes of course people run wider wheels... the Cortex suspension does NOT allow for more spacing inboard on the rears. The shock mounts in the exact same place. We have custom mounts to move the bump stop that allow more room but there is only about 1.5" to play with. I run 11.5 in the rear and its all I can do to keep the wheel mounted in the correct offset and under the fender. Nearly ALL of the wide body wheel moves OUT. This is one reason it creates even more push. Please call Filip. He'll explain that the 315 combo at all four corners is optimal for performance. He'll also tell you the wide body conversion is all about the look... nothing else.

 

EDIT: Just for frame of reference, my car on the left is a full CorteX equipped GT500 (W/L and T/A) and race JRi coil-overs. We built one-off wheels to maximize the tire while maintaining the correct geometry. This is a subject I'm very familiar with. The car on the right is the HyperStangs Hellanor, a 1500hp BMR equipped wide body (rear only) which we designed. It was initially going to be a full wide body, but the front geometry could not be corrected properly with the Shelby spec wheels. We opted for 10.5 fronts and 285's. A HUGE rear bar would help transfer weight in the back to offset some of the meat on the back, but with almost no slop angle this car would not be nearly the canyon carver as my car.

Edited June 5, 2016 by HyperStangs

[Ed07]

 

I think you're misunderstanding actually. The wide body does NOT widen the wheel around the thrust line and the proper pivot point.

 

Help me out here, when you refer to “thrust line” what are you referring to? My understanding is that the “thrust angle” needs to be ZERO otherwise the car will track weird. It is the angle relative to the centerline of the car running front to back. That isn’t going to change here. The “thrust line” is the *direction* the car will track relative to the center line of the car *if the thrust angle is set to something non-zero*. The S197s are solid axel cars so usually proper adjustments are made during an alignment. Cars with independent rear suspension are a different animal, but they’ll [hopefully] be set correctly but the alignment shop as well. What other “thrust line” are you referring to that I should be concerned with?

 

the Cortex suspension does NOT allow for more spacing inboard on the rears. The shock mounts in the exact same place. We have custom mounts to move the bump stop that allow more room but there is only about 1.5" to play with.

That is fine. I was just posting what Filip had originally told me—that the rear wheels could have up to 8.25” of backspace. Is this incorrect? That was my starting point.

 

Nearly ALL of the wide body wheel moves OUT.

Yes, but I’m working with what we already know about bone-stock s197 Mustang rear wheels and fender well clearances.

 

Please call Filip. He'll explain that the 315 combo at all four corners is optimal for performance.

Yep, the s197 seems to like a square setup. I’m not racing the car though.

 

He'll also tell you the wide body conversion is all about the look... nothing else.

Yep, I agree. If I’m not mistaken, I even believe Shelby says the same thing. I don’t think they mention anything about improved handling.

 

We built one-off wheels to maximize the tire while maintaining the correct geometry. This is a subject I'm very familiar with.

 

Ahhh, now we’re onto something. I believe I already mentioned that when the time comes, and if i opt for the rear wide body install, then the wheels will be custom for the car. But let’s back up. . .

I was only doing some spitballing with the numbers I had available. If you go back and look, I was using a very *conservative* 11” wide rear wheel in my calculations. If you scroll up you see that a wheel that is 11-inches wide with a 58mm offset (ET) will provide a backspace of roughly 8.25” and only move the tire and wheel about 0.7” outward toward street-side over the stocker setup. If you’re telling me you crammed an 11.5” wide wheel underneath the rear quarter without rub, then that tells me that depending on the tire height, it’s probably okay for the rear tire to protrude outward from the well slightly because it will never hit or there is more inner backspace clearance available.

Checking your numbers. . .

You’re running 315s but Im going to guess it’s either 315/30/20s or 315/35/18s (probably keeping close to stock height) on 11.5” wheels

With a 58mm offset the wheel and tire combo will protrude an additional 0.9 (almost an inch) further street-side over the 235/55/17 stockers and have (roughly) an 8.5” backspace.

And make no mistake, I appreciate all the feedback. Very good information.

Edited June 7, 2016 by Ed07