Ed M.

OK guys, I've been scouring the Net trying to find information on MAX wheel and tire sizes. I think we need to determine for certain the absolute biggest wheels that can be safely shoe-horned onto the 2005-07 Mustangs.

First, I'd like to determine the *widest* wheels and tires that I can squeeze under the rear fenders WITHOUT any suspension or fender mods. In other words, since I'm not looking to do any modifications to the fenders or the suspension (at this time), what's the widest tire that will fit the factory setup? I want to avoid ANY rub... I don't want the slightest rub or scraping at all. I've heard that people have been going all the way up to 315's in the rear with 20-inch wheels without any problems at all. I know that a (seemingly) factory/stock Shelby I looked at recently had 285's in the rear,* and someone I saw at a local "cruise night" here in NJ had 305's in the rear and 275's in the front of his 2006 Shelby. Going with 285's, or even wider would be pretty sweet looking if it's possible. The "deep dish" style would definitely give the car a much more "aggressive" look. *

I checked out some wheels that Mustangtuning.com was offering just to get an idea, and I don't plan on going with that particular style, but the "deep lip" effect is something I'd like to achieve with my car. I just want to do it right and not make any stupid mistakes.*

I'd like to go with the widest tires possible in the front as well. Again, the widest that will fit the stock factory setup (for now). This is where it gets a little tricky because I've heard that If you go with any width above 255's in the front the car will track and steer awkwardly. This would be unacceptable and probably dangerous! On the other hand, this could all be nothing to worry about - we'll see. In any event, during my internet searches I read of people claiming to have put 275's on 20" wheels on the front of 2005+ Mustangs!*Thoughts? Suggestions? Steeda and Saleen both claim 275s are just fine in stock front wells with stock GT suspension. 285s in the rear. Still need to know the wheel parameters before I can order a set.

It also might be worth mentioning that I eventually plan on lowering the car and adding all the appropriate suspension parts in the future. In the mean while I'm gathering as much information as I can,*I'm searching for spot-on specifications for the optimal offset and maximum front and rear tire widths for both factory as well as for modified setups (i.e. a car that's been lowered). It would be interesting to know the differences and limits for both setups.*

I like the deep dish/low profile look. The specs. I jotted down from a stock 2006 Shelby I seen while at a local cruise night was as follows:

305/25/20's on the rear.*
275/30/20's on the front.

Just throwing sizes around doesn't really help. If people are going to order wheels be it custom or something off the rack, we need to determine the following parameters that will dictate the absolute widest tires for both front and rear of the car:

1. MAXIMUM SAFE BACKSPACING (So as not to interfere with inner fender-well or suspension components)

The easiest way to measure backspace is to lay the wheel face down onto the ground so the backside of the wheel is facing up.* Take a straight edge and lay it diagonally across the inboard flange of the wheel.* Take a tape measure and measure the distance from where the straight edge contacts the inboard flange to the hub mounting surface of the wheel.* This measurement is backspace. We need to determine the safest maximum for both front and back wheels and tires.

2. MAXIMUM OVERALL WHEEL WIDTH.

Measure across the entire wheel from the the inside flange to the outside flange.

3. WHEEL CENTER-LINE

Is the overall wheel width divided by 2.

4. OFFSET (Measured from the rim center-line to the inside face of the mounting hub)

- Wheel Backspace (determined in 1.)
- Overall Wheel Width (determined in 2.)
- Wheel center-line (Determined in 3.)

To get OFFSET subtract wheel center-line from wheel backspace.

In other words: wheel backspace - centerline.

- If backspace is less than wheel center-line the offset is negative.
- if backspace is greater than wheel center-line the offset is positive.
- if both backspace and center-line are the same then the offset is zero.

Another way to look at whether the offset is positive or negative is noticing whether the inside face/surface of the mounting hub (the part of the wheel that touches the brake rotor) sits further back from the rim center-line or in front of the rim center-line.
- If it sits in back of the rim center-line it's negative.
- If it sits in front of the rim center-line it's positive.
- If it sits flush with the rim center-line it's zero.

I'm also curious about how these tire and wheel combos will affect overall ride quality.

Thanks in advance for any information and suggestions you can provide!

--
Ed Magg

StangFreak

Bolt Pattern: 5x114.3 (5x4.5)
Offset Range: 25 to 45
Wheel Size Range: 17x8.0 to 22x9.0
OEM Tire Size (Front): 235/55-17 (235x690 mm)
Max Tire Dimensions: 275x715.0


From Bigwheels.net for 2006 Mustang GT

Infinity

Rear can take an 11.5" wheel with a 325mm tire on an 8.375" backspacing (I'm unsure what that translates into offset, but I THINK it's +70mm)

Front can easily take a 10" width with a 275mm tire on +45mm offset

Ed M.

StangFreak, thanks for the heads-up. I checked BigWheels too and I'm guessing that they list that for liability reasons. The 275s for the rear seem conservative when factory Shelby's are shipping with 285s, so it's hard to tell. And I have personally seen 305s in the rear of a 2005/06 at the time. Not sure which brand wheel though.

Infinity, where do you get your numbers? I ask because they seem a little high. 325's?? Is that even safe? Can anyone else confirm those numbers? We'll need to get the parameters for a wheel that size. If we use 8.375 to be the MAX BACKSPACE without any rub or interference we get this:

Centerline = (11.5/2) = 5.75 inches
Offset = (Backspace - Centerline) = (8.375 - 5.75) = +2.625 inches = +66.675 mm

Positive offset because backspace is greater than centerline.

Can anyone else confirm these numbers? Are they safe? Any wheel-tech. guys lurking in these forums? Hopefully we'll get confirmation either way.

Thanks for the feedback guys. I'm hoping that this thread can help provide accurate information for people looking to see what the absolute widest (and still be safe) tires their 2005s - 07s can handle on a factory config. It will go a long way for people having custom wheels made. They'll need these parameters for whichever company they plan on using.

Basically it should eventually distill down into accurate, readily available specifications that someone can simply look up and say:

"These are the wheel parameters defining the largest (and safest) possible wheel and tire combo I can fit in the rear of my 2005+ stang. It will give you a whel that is "x" inches wide and a tire that is "y" millimeters wide" . Ditto the front.

Remember, there can be absolutely ZERO body/fender rub during hard cornering or while taking turns on less than perfect pavement etc. and there can be no interference with any brake or suspension components either.

--
Ed

Infinity

I got the numbers from what I've seen on the cars actually being used. I have seen in person, 10.5" rears with 315/35's, with 1.5" lowering- +45mm offset. NO clearance problems. The 11.5" rear was from a guy on the Corral, and he gave me the backspace measure. I'd like to try the 11.5 or a 12 with the 345/25/20, but the wheels would be $$$$$$. I think the biggest problem people are having is they're not using enough offset, thereby placing tires too far out. It seems everyone automatically recommends a blanket +45mm offset, when that number would be different depending on the width of the wheel itself.

StangFreak

Tire sizes on Big Wheels are conservative. If you look at some of the wheels they sell, they are as wide as 10 inchs with a max tire size of 295 mm. For a no hastle fit, that's as large as I would go.

Ed M.

Infinity, I did some quick math and determined that a wheel with a (positive) 2.625-inch offset (66.7 mm) would yield a wheel with an outer lip of between 2.5 and 3 inches. Can anyone else confirm that? Does that sound right? Can you have that large of a lip (deep dish effect) on the 2005+ Mustang real wheel wells?

--
Ed

Ed M.

I think if we knew the absolute MAXIMUM amount of (safe) backspacing for the rear of the 2005s+ (I have a 2007) we could determine the rest of the wheel parameters. Anyone know what Ford uses on the 2006 Shelbys with regard to the backspacing? Is there any more to be had? Perhaps Ford was conservative.

--
Ed

Infinity

I know for a fact that the 10.5" +46 mm fits with a 315/35/20. The Axis GT-R was made specifically for these cars. Using that as a guide, and the guy that has them claims 2+ inches of rear clearance, we can work a little bit from there.

I never figure by lip size as that is in some ways determined by the style of the wheels themselves. Again, though, there is a severely lowered car on the corral running 11.5" wheels with the 8.375" backspacing. I'll find a link to the thread. http://www.corral.net/forums/showpos...68&postcount=8
I PM'd him afterwards for the information.

Ed M.

OK, that's a start. I'm more interested in exactly where that 2-inches of clearance *is*. Is it toward the inside fender well or the outside?

305's seems pretty nice. I'm guessing with the 11.5s he's already at the limit with what will safely fit. Maybe he'd be kind enough to share his information with us and fill in the blanks wrt our wheel parameter questions. Still with that 11.5 wheel I see very little wiggle-room. It would be interesting to know if there is any rubbing or scraping during turns and cornering; especially while there is suspension travel over uneven surfaces. Let's put it this way... If he has those wheels then taking measurements is all we'll need. We'll also need the clearances for either side - i.e., both the outer tire-to-fender lip and the inner-tire-to-wheel well.

--
Ed

Ed M.

Well, In case anyone is interested, I did a little research and one CarCraft article from March of 2000 recommends between 1/4-inch and 1/2-inch subtraction when measuring for backspacing in order to avoid the contact points.

What they are saying is that if you measure the distance from the face of the mounting pad to the first contact point in the wheel well, you need to subtract about a 1/2-inch for clearance and another inch for tire bulge and suspension flex/body-roll. That's amounts to an inch-and-a-half LESS than the total backspacing - mounting pad face to contact point in fender well. I just might invest in a tool to measure it myself or maybe i'll just rig something up. The same clearance should apply to the outer lip of the fender as well. That would suggest roughly 3 inches subtracted from the overall wheel width measurement.

basically what it's saying is that if your total fender well width is 15-inches measured between its surfaces, inside and outside at its closest points then the maximum wheel width would be 12-inches. there will still be 1/2-inch clearance on either side of the tire. 1/2-inch between the tire and inner fender-well contact point and 1/2-inch between the tire and outer fender lip.

Does that sound about right?

The front might be a little trickier because going with a tire that's too tall and wide still might scrape on stuff while turning into a driveway or onto a ramp or turning in general while on a less than ideal driving surface. This is due to suspension travel/cycling. Anyone else note any different findings?

--
Ed

Infinity

That sounds reasonable. And I agree, the front will be a bit trickier to measure. But, our own Official_STyle runs a 10" front wheel, with 285 width tires, and +45mm offset. We need to get him involved for some measurements. Lest we not forget, if the car is lowered, there may be some contact points come into play that aren't an issue on a stock suspension.

1 COBRA

You might like to research the relation between the combination of a heavy car with wide tires and hydroplaning.

Anyone who has ever experienced being on an interstate highway or expressway when pouring rain will confirm keeping a car under control is not only a challange but very frightening.

You can become a drifting expert real quick. I know I did.

Ed M.

OK, now we are getting somewhere. I just received an email from Greg Smith over at Weld Wheels and he stated the following:

"7.88" is the limit to account for tires up to 305mm section and leave
room for the sold axle to articulate plus bushing deflection."

That means 305 appears to be the "safe" limit on a 10.5" wheel. that's a half-inch shorter than the 8.375" of backspacing previously listed. Unless Weld is being conservative. I think what I'll need to do is rig up a contraption and take some measurements myself - unless someone here has already done it.

--
Ed

Ed M.

So, what do you guys think, are these conservative limits? I was hoping for some feedback from people that have already been through this so we talk about it here. It will provide a place to get quick and hopefully accurate information.

--
Ed

Infinity

They are conservative. I know several who are running 315's, and one who has 325's (drag wheels only, so I doubt it gets much side-to-side). IDK if I'd trust Weld to be the experts- they sent someone a set of wheels that were "made" for the S197, and it took them approx. 1 year to finally send him the spacers so the wheels would actually fit.

I've seen a measurement tool, it was on e-bay. I'll try to find it again.

vc4life

Infinity dont forget that car has the 3D carbon body kit which has fender flares so that wheel might have less back spacing or might not tuck the stock fender

Infinity

True. He's put 11's on the rear of some others, but I couldn't find the pics. I'll check again.

Here's 20x10 all around- still looking
http://www.corral.net/forums/showpos...44&postcount=1

http://www.corral.net/forums/showpos...59&postcount=3

Found it

http://www.corral.net/forums/showpos...48&postcount=1

The guy doesn't like to give ALL his information- hell, he sells the stuff. But, he does answer questions if you ask. That, and he's made some beautiful cars. I wonder if a 345/25 will fit on the 11.5" wheel? That'd be stock height in 20", and a 345/30/19 is available, and would be stock height. I just don't know if we have THAT much space!?!?

06blkmustanGT

**** 11.5 here i come. anyone got any info on offset and backspacing?

Infinity

8.375" BS, I don't know exactly what that translates to in offset. It seems to be about +62mm, but I'm looking for a calculator to get an exact number.