Finally new tires

[Gabe]

I vaguely remember reading somewhere that Ford had intended the early-year S197 GT500 to run a 'square' tire setup, but couldn't get that arrangement to meet some internal standard or other. I don't think any mention of tire size or wheel dimensions was made, but I have a sneaking suspicion that it might have been 255/45-18's all around, likely on 9" wide wheels.

Adding half an inch to the wheel width would have still permitted the use of 255/45's up front, and opened up the possibility of running 285/40's out back (essentially the same diameter).

A lot of speculation there, but keep in mind Ford's very conservative philosophy in choosing tire sizes at the time ("regular" GT's didn't get anything beyond 235-wide tires in 17" initially, according to a MVMS document).


Norm

Yes. Originally the 2007 GT500 was set to have 255/45/18 tires all around.
Carroll Shelby drove a prototype and told Ford the car needs more rear tire.
So the car got the staggered sizes, 255/45/18 front and 285/40/18 rear.
I don't know anything about the width of the wheels on the prototype Mr Shelby drove, I'm only assuming it was production-spec, so 18x9.5"

They're visible pretty well in this video, and they seem like black versions of the 2007-2009 GT500 stock wheels:

Gabe, did you ever check to find out if they cleared the front strut when at full lock turn without the 5mm spacers? Also when you added the spacers, did you need to get longer wheel studs? My understanding is wheel spacers 5mm and above require longer wheel studs

I'm still running factory studs, even with the 1/4" spacer (I measured it, it's 1/4").
I've autocrossed on this set-up, driven up to ~130 mph, and just plain enjoyed a wide front tire for about 3-4 years now, about 15-20k miles.

I'm not sure I understand what you mean by clearing the strut when turned.
The wheel turns WITH the strut, not toward it.
Personally I've never noticed any difference in clearance there, whether straight or turned. Not sure I really checked though.
I know I put a bunch of miles on the set-up without the spacers, and there were no signs of contact anywhere on the tires or the wheels, so I thought I could safely assume "no contact".

After testing fitting one of the rear tires up front, the good news, it does fit. The bad news, it does not clear the front strut assembly when at full lock turn. Therefore I would not recommend running 285/40/18" tires up front without first adding spacers.

Well, one thing to remember is that every tire model is different.
The Goodyear Eagle F1 runs wide, Nitto 555R runs narrow.
The picture below is a Nitto 555R 305/40/18 tire on the left and a Goodyear Eagle F1 285/40/18 tire on the right. Both are mounted on the same 18x10 wheel.
There's almost no difference in width. Which probably is the main reason that I was able to run the Nitto 555R in that same 305/40/18 size on the FRONT of my '13 GT, and even autocrossed with them on, with no rubbing (second picture below).

 

[Smokievol]

I'll try out the 280/35/19 at the tire dealer on the fronts to see how they work. Plus the 275/35/19, which should works. Still looking at going with 275 on fronts and 285 on rears, may change all 4 to 275.

 

[Smokievol]

Great Video to watch, Plus I can't believe those two tires are so close in actual size with the specs they have I can see where the 285 will work upfront with Nittos being that much more narrow. After looking at those pics, may change to a square 285/19 set up.

Maybe 305 in the rear???

 

[Gabe]

Great Video to watch, Plus I can't believe those two tires are so close in actual size with the specs they have I can see where the 285 will work upfront with Nittos being that much more narrow. After looking at those pics, may change to a square 285/19 set up.

Maybe 305 in the rear???

Not on 9.5"-wide wheels.
A 305 really wants a 10.5-11"-wide wheel, otherwise you'll get sidewall bulge and a decreased contact patch.

 

[06 T-RED S/C GT]

Yes. Originally the 2007 GT500 was set to have 255/45/18 tires all around.
Carroll Shelby drove a prototype and told Ford the car needs more rear tire.
So the car got the staggered sizes, 255/45/18 front and 285/40/18 rear.
I don't know anything about the width of the wheels on the prototype Mr Shelby drove, I'm only assuming it was production-spec, so 18x9.5"

They're visible pretty well in this video, and they seem like black versions of the 2007-2009 GT500 stock wheels:

I'm still running factory studs, even with the 1/4" spacer (I measured it, it's 1/4").
I've autocrossed on this set-up, driven up to ~130 mph, and just plain enjoyed a wide front tire for about 3-4 years now, about 15-20k miles.

I'm not sure I understand what you mean by clearing the strut when turned.
The wheel turns WITH the strut, not toward it.
Personally I've never noticed any difference in clearance there, whether straight or turned. Not sure I really checked though.
I know I put a bunch of miles on the set-up without the spacers, and there were no signs of contact anywhere on the tires or the wheels, so I thought I could safely assume "no contact".





Well, one thing to remember is that every tire model is different.
The Goodyear Eagle F1 runs wide, Nitto 555R runs narrow.
The picture below is a Nitto 555R 305/40/18 tire on the left and a Goodyear Eagle F1 285/40/18 tire on the right. Both are mounted on the same 18x10 wheel.
There's almost no difference in width. Which probably is the main reason that I was able to run the Nitto 555R in that same 305/40/18 size on the FRONT of my '13 GT, and even autocrossed with them on, with no rubbing (second picture below).

View attachment 72567
View attachment 72568

Very awesome find on the video and very informative Gabe. Anyhow what I meant to say was when turning the wheel full lock, part of the tire would make contact with the inner wheel well next to the strut tower. Therefore my mistake for not clarifying accurately lol. Also the clearance issue was with the stock Goodyear Eagle F1 for which you did confirm runs a bit wider, so perhaps that was also a contributing factor behind the clearance issue? At any rate, It appears the Continental Extreme Contact Sports are the only tires I'd be interested in that are available in 285/40/18" sizes. Otherwise, I may end up considering Firestone Firehawk Indy 500's in 275/40/18 instead

 

[Aerofinz]

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