Infinity

Found a conversion. The 11.5" wheel would have a +54mm offset. There's a formula at the Mickey Thompson site.
http://www.mickeythompsontires.com/t...p?bulletin=s10

06blkmustanGT

well someone needs to be the guinea pig and give it a try (i wish they made bullitts in that size)

Infinity

I should have the $$$ by spring, when I plan on new wheels anyway. It's too late to get the nice ones now.

Ed M.

As I posted earlier in this thread, I ran the numbers and got this:

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 (after conversion)

Or about 67 mm (positive offset)

That's using the math found on this page:

http://www.rsracing.com/tech-wheel.html

Anyone else care to run the numbers again? Since the M/T site didn't give too much detail, I'm inclined to use the calculations from the above site.

--
Ed

Infinity

Ed, I don't think your numbers are taking the mounting pad thickness into account. Or...maybe mine aren't. Your numbers make sense. Do offset/backspacing figures include the mounting hub, or do they just figure from wheel center, making some of the numbers possibly inaccurate?

06blkmustanGT

i believe that its measured to the base of mounting hub not sure though

Infinity

I think we're making this too difficult. 10.5" +46 fits for sure. If we want 11.5", we must add 1/2" metric (~13mm) to the offset. So, about 60mm would be fine, which also comes close to the same figure Ed had above. If only 5mm makes a difference, then we were too close to the edge anyway.

Ed M.

Hi guys, I've been looking at the images again that appear on the web page (I posted the link above). It looks like they are measuring from the back side of the wheel. From what I can tell they are doing the following:

- To get an absolute accurate measurement they are placing the wheel face-down
(the part you see when it's mounted on the car)

- With the the back bead/flange now facing upward they are running a straight edge
across that bead/flange backside (the inside part you don't normally see)

- They now take a ruler and measure the distance from where the mounting surface
of the hub is (i.e., the surface that contacts it's counterpart surface on the disc)
up to the straight edge and reading the measurement.

This makes perfect sense because it can effectively eliminate any concerns for hub thickness. It's measuring to/from the back-side of the hub, it's mounting surface. At least that's the way I read it.

The centerline will always be the total wheel width divided in half (or by 2) - whatever.

I ran the numbers again and they seem to make sense. I'm still getting a +67 millimeter offset with that particular backspacing of 8.375 - inches.

If you click on the link above and look at the last wheel cross-section diagram toward the bottom of the page take note that the right side is what would be facing outward and the left side is what would be facing inward toward the centerline of the automobile itself.

If 11.5-inch wide wheels can be used then the following questions must be answered:

1. How much space remains on BOTH the inside and outside of the wheel? We'll need two
measurements:

a. The distance between the inner flange/bead of the wheel and the nearest contact point
in the inner wheel well area. Note that we aren't even taking into account the tire just yet.

b. The distance between the outer flange/bead of the wheel face and the nearest contact point
on the inner lip of the rear fender/quarter panel. Again, as above, we aren't taking into
account the tire just yet.

2. Will this leftover space (along with a mounted tire) be sufficient to avoid any rubbing while
the car is experiencing heavy lateral forces such as cornering and the like? Does it take
into account the fair amount of bushing deflection that these forces impose?

It is of the utmost importance to make sure there will be ZERO contact - not only because it's dangerous, but because it can ruin the wheels, the tires and your car. Besides, it would sound horrible too.

Remember, these measurements are to be taken on non-modifide cars. Only STOCK fenders and quarters!

--
Ed

Infinity

Now, where to find a donor wheel or blank to test with. I'd even be happy to chip in a bit of money to get this information. None of the custom wheel companies have been very forthcoming with any information. I've tried CCW, Iforged, HRE, and GFG. None will work with me to find this info. But they're ALL happy to build wheels at $1200+ each

Ed M.

Aren't there manufacturers of special tools for determining exactly what we are looking to accomplish? I know I can rig up a contraption using some angle-iron and some threaded rod, but would rather buy a nice accurate tool if something exists.

--
Ed

Ed M.

Has anyone seen or used this before?

http://store.summitracing.com/partde...5&autoview=sku

--
Ed

Infinity

That's the thing I'd seen on e-bay that I was looking for. Seems a bit expensive for what it is, but I think it would accomplish what's needed here.

I e-mailed Percy's HP to see how wide the tool can measure. It will do 30" diameter, so we're covered on that end.

Ed M.

Looks like we are covered on Width too

http://www.jegs.com/webapp/wcs/store...tegoryId=11615

The question is... What's the MINIMUM clearance allowed between contact points? We can use that and even allow for a bit more clearance to be on the absolute safe side. Anyone know how much deflection there is on the new Mustang GTs with factory components?

--
Ed

Ed M.

I just took a really quick measurement of the rear fender well. I measured from the fender lip to the inner wheel-well wall and measured about 13-inches. Can anyone confirm that using a regular tape as I did? Just curious that's all. Anyway, 305s would put the overall width at exactly 12-inches and I seriously hope that includes any tire bulge or deflection because that means that there would only be about a half-inch clearance to either side - and that's assuming that the distance in clearance will be the same on either side of the tire.

Thoughts? Personal experiences? What do you guys think?

--
Ed

Ed M.

Well, I ordered the tool from Jeg's. It should be here by this Wednesday. I'll take some measurements this Saturday and post them here. Anyone find out anything new? The thread got kinda quiet.

--
Ed

Glenn

http://www.carcraft.com/techarticles.../photo_01.html
some reading while we wait till wed

Infinity

Been outta town. I gotta catch up soon.

Ed M.

Well guys, I received the tool. It was 80 bucks shipped to my door. After first inspection I'll be honest, it seems really cheap and flimsy. Perhaps I'm being a little too hard on the manufacturer. What's more, it's made from plastic for crying out loud... Sheesh. Doesn't seem too precise at all - that is if you go by the markings on the thing. I'm still attempting to figure out how to use it. The numbers on the thing seem to be meaningless. Seriously.

At the moment I'm attempting to ascertain the difference between the observed measurement as represented on the tool itself, and the actual measurements when I lock everything into place and measure it with a tape or rule. So far I've noticed that they "stepped" the tool to provide an offset for brake calipers (guessing). That's not a bad idea except they forgot to "square" the foot that attaches to the tool's plastic hub so the inner mounting flange surface (the part that presses up against the rotor) can provide an accurate point of reference on the slider adjusting arm. It's off by between 1/2" and 3/8".

So far the only thing that can accurately be measured with this thing is the "overall" (wheel + tire combo) width that will fit. You just have to ignore any of the markings on the thing and just use a tape to measure the distance from one end to the other. Just seems like they could have done a much much better job if they really wanted to - especially for the price. I'll try it out nevertheless. Oh, and don't even get me started on the directions that came with the thing... Absolutely horrible.

Here is how I plan to attack the situation:

1. I'll work backwards and try to determine the maximum *tire-and-wheel* width first. In other words I'm going to attempt to come up with a measurement that will be considered the absolute max width of a mounted tire + wheel.

2. I'm going to use the tool to measure the absolute width of the wheel well from contact point to contact point. This will provide an initial point of reference and at least tell us how much room we have available.

3. I'll then subtract 1/2" from either side. This measurement will be the mounted (tire + wheel) width accounting for any bushing/tire/suspention etc. deflection. This is saying that we'll provide 1/2-inch of space on either side of the tire before it comes into contact with anything.

3. We'll need to see what wheel + tire combo is available that will give us the "overall" section width we are looking for, but again we need to know what the section width would be with the tire mounted on the wheel. Once we know that we can then figure out the other parameters. We'll need to determine the proper backspace and offset before ordering the wheel.

The key is to figure out just how much space we have available and allowing 1/2" on either side of the *tire*. Does anyone believe that 1/2" is too little to allow for tire clearance?

--
Ed

SUBZERO

Sorry guys, slightly off topic, but since you all seem to know a lot more about wheel fitment than I do, I figured I would ask my question here.

Will 20x10: rear and 20x8.5" front fit the 05+ cars with a 40mm offset all the way around? This is the highest offset I can get in the style of wheel I want to order. I don't plan on using any larger than a 315/30 series tire on the rear and more than likely 255/35 on the fronts.

06blkmustanGT

40mm offset will work in the front but needs 45+ in the back. and 315s will bulge a little on a 10 inch wheel so they will stick out a tad more. and the only available option for 315 on a 20 is 315/35 (little taller sidewall)