AlkyIROC

I finally have some pics of my own inner fender modifications.



Whenever someone asks about modifying the inner fenders for bigger tires, I always post this picture. I can't remember who's car it is but it's a good picture to use. Look at this pic compared to my own.



This is the front. You can see I didn't resection the inner panel but I did cut off the extension that drops below the floor level. There's some hammering in there to extend the inner panel where the tire was just starting to rub. You can't see any of it now. A bit of spray paint does wonders. The driveshaft is disconnected because I was doing some centerline measurements.



The back part. Because my diff is set back about an inch, I had tire growth issues. You can see where I cut the lip off the outer fender and ground effect. This left a gap between the inner and outer fender. I hammered and pinched them together then filled the remaining gap with a body caulking. The ground effect is cut off just forward of the mounting bolt area so if you look at a stock one, you can get an idea of how much I had to cut off. You can also see where the bump stop has been cut off and plated over. Those are Ford 11 x 2-1/2" drum brakes. It was the easiest way to install brakes on the 9" and they supply more than enough stopping power. The other side looks similar except that the spare tire indent has been hammered back into the car.



The tire on the right is what I've been using for the last couple of years. MT ET Drag 29.5 x 10.5 mounted on 15 x 10 rims with 5.5" backspace. Putting a ruler across the tread is actually 10". Compared to a normal tires, it's big. On the left is what I hope to stuff under the car over the winter. Those Hoosier tires are old but I'm just using them for measurements. They're 32 x 14 and across the tread is 14". They're mounted on 15 x 15 rims. The height difference is deceiving because the angle I'm shooting the pictures at. They won't fit under the car as it now sits. A back half needs to be done.

nelapse

iTrader: (17)

so... whatcha doing with the old tires

AlkyIROC

Old tires are just about worn out. I squeaked through to the end of the season. There's still enough rubber on them but they're starting to get a little dry. There's a bit of a gash in the tread of the other tire where it rubbed the rear part of the fender. Tech knew about it and agreed with me that it wasn't into the cords so they let me finish out the season on them.

Sonix

iTrader: (1)

What about shoving the new tires further out? (rather then further in to tuck them in nicely, and needing to back half?). I'm just thinking, a race car isn't a show car, is there another reason to tuck them in?

The back-halfing (as I know it), gives more inner room. Does that make your fender wheel mods moot? Also, what is needed for the tire height? Modifying the outer lip of the wheel well? Use 4th gen spring isolators and simply jack the car up more?

AlkyIROC

With the car supported and the diff hanging down, the tires fit. I did that to do some measurements. It's not possible to install the big tires on the car without major surgery. The rear fenders would have to be entirely cut out. Because of the backspacing on the new rims, the tires stick about 10" outside the fenders.

Doing a back half completely removes all the inner sheetmetal that you see. New frame rails are installed roughly in line with the rear bars of the roll cage. Wheel tubs are installed as the inner fenders and new sheetmetal is attached over the frame rails to fill in the rest of the gaps. You don't want tires sticking out. Tuck everything under the fenders for a cleaner look. If I want open wheels, I'll get an altered.

As for more tire height, the back of my car already sits high enough since so much rear weight has been removed. Look how much room I have above the tires already. It's not a height problem. It's the size of the opening from front to rear. If my axle sat in the stock location, I wouldn't have the rear part of the fender rubbing on the tire but the front inner part of the wheel well would need a lot more sectioning.

Sonix

iTrader: (1)

oh, ok. So the tall tires main mod point is the front to back wheel well dimension.
So with the wide tires, you're going to use different backspacing wheels, and you're going to completely back half it? Interesting, you'll have to show pictures of that when it's complete (or during the working stages).

AlkyIROC

Both rims have 5.5" backspacing. I really wanted some with 3.5" backspace but got a good deal on these Pro Stars. Old rims are 10" wide. New rims are 15" wide. With the diff dropped down to fit the new tires on, they still fit fine along the frame rail but have clearance problems at the front inner part if the fender was cut out enough to move the diff back up to ride height. The tires are so huge that most of the tire is outside the fenders. From all my measurements, the diff needs 16-1/2" cut out of it to get the tires under the fenders but I'll probably be cutting up another diff since I could always sell off this one.

Nothing has been started yet other than pulling the tires off and doing a bunch of measurements. Although I have a lot of parts to do a back half, there's still a bunch more I need. I'm currently considering just buying a rear subframe 4-link kit to make the job a lot easier and say goodbye ladder bars. That way I could always sell the diff complete with the ladder bars since it doesn't have a torque arm mount but does have all the other third gen suspension brackets. I would still need the center section. S&W currently has a sale on back half kits until the end of the year although I don't require the entire package.

83 Crossfire TA

iTrader: (2)

I think that those pics make it pretty clear that someone isn’t getting 29.5” tall tires in completely stock wheel openings, much less wheel well.

Moving the axle back about an inch avoided most of the fit problems that people run into right away with the inside front of the wheel well. I’ve been running some 275/60/15 bfg DR’s on 7” (I know) rims which should be about 28” tall and a little over 10” wide a the sidewall bulge (at some point I measured exactly and posted on here, but I don’t remember right now).

Looks like what you gained in not having to screw with the front you lost in having to mess with the back. Do you have any pictures of the passenger side, I’d be much more interested in seeing that. On my car, even with the tires being really worn down I was getting rubbing in the middle of the tread at the back of the wheel well where the spare tire bulge was I get the impression that for some reason this is not as big a problem on the camaros. In my case I’m sure that the problem is worse since most of the time the car has either cut stock springs or eibach pro’s and no rear spring isolators installed (really, the suspension is setup for handling), so it sits probably an inch or more lower then stock.

Those of you that have cut out the bump stop/spring lump and plated over it, where you actually hitting it while you were running? Do you ever hear the spring rubbing that plate? I don’t appear to have any issues with it with the 275 60’s, but when I ran a set of 275 50’s, even with them sticking way out (on a set of t-type rims with 0 offset, should be about like hour 10” rims with 5.5” BS), they didn’t come anywhere close to the inner wheel wells like the taller tires do, but you couldn’t put the tires on with the axle drooping because the tire bulge would get in the way of the bumpstop.

What are you planning on doing under the hood to need all that extra tire?

AlkyIROC

Under the hood is fine, finally! The extra tire is for consistency. Sure I was able to run 9.754 twice in a row a couple of hours apart but it must have been a fluke. A bigger tire means much less of a chance of spinning off the line. I'm sure I'm spinning those 10.5's no matter what I try or how well the track is prepped.

83 Crossfire TA

iTrader: (2)

Anything with the rest of my coments/questions? What happened with the spare tire lump and other issues on the passenger side?

83 Crossfire TA

iTrader: (2)

Ok, I decided to play with this a little bit… this is my formula, with either eibach pro kit springs or pro’s on the front and cut stockers in the back (they sit at about the same ride height). The tire is a 275/60-15 BFG DR (slightly taller then 28” tall), the front is a 215/65-15 (right around 26” tall). Mind you, these are on stock, .5” offset wheels, they’d be like 15x10’s with 6” BS…


Now looking at that it doesn’t look like there should be nearly the problem with fitting the 29.5” tall tire as it looks like from your pictures, especially in the front of the wheel well. The picture is shot from dead on the middle of the side of the car, so you’re seeing a little bit of the tread on the front side of the tire, so the tire is actually a little closer to the back of the wheel opening. Here I added some marks to make things easier to see (you may want to make sure that your browser isn’t scaling images to see things clearly, sorry for the large picture but everything that I tried to make it smaller hid the details). The arrows behind the tire show the outline of the spare tire bulge and it should be pretty clear why it contacts the tread surface of the tire. The cross through the center of the tire are just to help me scale the tire and then put it back in it’s original location.


Finally, here I scaled the tire to 29-1/4” tall (I’ve wondered about 29” tall tires, you mentioned 29.5” tall tires, conveniently, something right in between worked out perfectly wrt to scaling). Interestingly, WRT to the wheel opening it really looks like there is plenty of room in the front, and if you’re going to have any issue with tire growth it would be in the back, so if anything shortening the LCA’s/moving the tire forward a fraction of an inch will probably let you run it without hitting the wheel opening.


Based on that, it really looks like on the right wheel, you could run a 29x9, maybe a 29x10 and even slightly taller by just squaring off the inner wheel well. I know that even with enough offset to fit the tire inside the wheel well, interestingly, it looks like a wider tire gets you into trouble on the outside faster then a taller tire. For example, that 275/60 works fine like it is, but a 295/50-16 (if I remember right with roughly a ¼” offset, I posted here with pics a while back), a slightly shorter but wider tire first has a problem with the fender lip at the top of the tire (probably woudn’t be an issue with stock ride height.

Thoughts?
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Of course, all that depends on cutting out the spare tire lump...

Sonix

iTrader: (1)

oh, just a side thought, look at izcains car.
295/65/R15 tires, which is a 30" tire. Wonder what he has done?
I know these aren't slicks, so WRT to the tire growth issue, it's moot, but it's still a damn big tire, and it doesn't seem like he has front to back issues. Maybe someone can ask him. That's one of the tallest tires i've seen on a thirdgen...

AlkyIROC

There are no other issues with the passenger side except the spare tire bump. Nothing a really big hammer didn't fix.

AlkyIROC

From the looks of it, he raised the back end up to fit the tires on. My car sits level with my tires. If I jacked the back end up about 4 inches, I wouldn't have had any problems either. Same goes with my 32" tires. If I raise the back end up a lot, they could fit but would stick outside the fenders so much it would look like an import with their low pro tires and 8" rims with 1" of backspace. Actually I saw a third gen like that the other day. He had some normal tires on some real nice rims but the had the wrong backspace and the tires stuck way out past the fenders.

83 Crossfire TA

iTrader: (2)

That’s exactly what I’m trying to avoid… Given the choice I’d rather end up with something like that 29.something inch tire but lowered another 1.5” or so, so it would look like:


Of course, I think that would be about the limit of what is really possible and maintaining any kind of reasonable suspension geometry (about 3” drop from the original ride height). It’s just about at that point that the floor pan and wheel wells need to be cut out, the body positioned where you want it and then the suspension and it’s mount points relocated depending no where they need to be then wheel wells and floor pan put back to cover what you end up with.

Makes you wonder why someone doesn’t make a nice, reasonably wide (>10”) 27” tall drag tire. I’d kill for a 255/60/15 or 295/50/15 drag radial (nitto for street use, MT for track use)