How to fit really big rear tires on an E body.

[gomopar440]

Someone PM'd me asking how I was going to be able to fit those 345's under my Challenger. Since it was a rather long reply post I figured I might as well make a public post out of it to share the info. That way everyone else can also see what it takes to go big.

Ok, are you ready for a legnthy auto shop class?

On the Challenger (and 70-74 Cuda) the first thing to note is you will not be able to minitub them as far as you would on an A body or B Body. On an E body the rear sub-frame rails are narrower at the front than they are back by the bumper. On an A or B body these rails go straight back. This means when you move the stock inner wheelhouses inward it will contact the frame at the back edge first and limit how far you can move it over. I was only able to get the inner wheelhouse moved inward an extra 1.5" on my Challenger. To go any further inward will require moving the rear of the frame rails inward until they're straight like the A's and B's. Then you can use any aftermarket wheeltub for the inside half of the wheelhouse. If I had to guess, I'd say you could get another 2-3" buy moving the frame rails and using aftermarket tubs. If you did this though you would remove the support stregnth for your rear bumper brackets. Not something I would normally reccomend doing if you plan on driving the car on the streets.
Here's a link for how to actually perform a minitub job.
http://www.bigblockdart.com/techpages/wells.shtml
Just remember that the frame rails are different like I mentioned above. Everything else is pretty much the same.

I just replaced the quarters on my Challenger and took the opportunity to trim the wheel opening lip down to about 1/2" wide. The aftermarket quarter panel and outer wheel house stampings had lips on them that were about 1.5" wide. So after trimming, I gained another inch of clearance for the tires there. After all the new metal was installed and the wheelhouse moved over and welded in place I measured the width of the wheel opening. I had right about 15" but you have to remember to subtract the  .5" for the lip at the wheel opening. That leaves me about 14.5" to fill with rubber minus clearances. The 345's are about 13.6" which would be a very tight fit. Backspacing will be critical to make that work. However, since I cant locate any 345's, I've decided to go with the next closest tire I could find. 335/35R17 which is about 13.1" wide. That leaves me with more breathing room for tire clearance and looks like it would be a better choice at this point.

The other major item to address is that the leaf springs will now be in the way after moving the inner wheelhouse over. The only real way to get them completely out of the way is to use a 3" spring relocation kit like MP offers. The offset front spring hangers wont be able to clear the new wheel well and will render your effort to widen the opening useless. So... don't even bother doing the minitub unless you are willing to also do the spring relocation. The spring relocation kit has a C-chanel shaped piece of metal that replaces a bend in the subframe. You haveto cut the bend out of the frame and weld in the C-chanel in it's place. Then you have to figure where the spring should go and drill holes for the front spring eye bolt. You can drill a few holes in different locations for some adjustability if you want but just remember, THIS PIECE IS NOW A PART OF THE FRAME STRUCTURE. So, don't get carried away. Ok? I plan on drilling two sets of holes. One for stock height and one for lowering the car about 1" You will also have to weld on a new spring perch onto the axle to keep it in line with the spring. Here's another link specifically for how to relocate you springs.
http://www.bigblockdart.com/techpages/springs.shtml

Ok, now I've given you the info on how it's been done before by others and myself. The rest is up to you. It's you car and you're responsible for any changes you decide to make to it. Good luck!

If anyone is interested in checking out my Challenger and the progress so far heres a link.
http://www.moparnuts.com/forums/showthread.php?t=3636
Enter at your own risk, it IS on Moparnuts after all...

[tactransman]

Yep .. been there.... done that.

[gomopar440]

Nice! How big of a tire were you able to fit under there after moving the rear frame rails and inner wheelhouse?

[tactransman]

13/13.5 Mickey Thompson. I think a 14 would fit with the perfect wheel offset but I did not want to cut it that close.

[gomopar440]

Did you have a stock E body width axle under there? If so how much backspacing did you end up using?

[tactransman]

I have a '69 B-body 8 3/4  housing and axles. It moves the tires in about 3/4 inch on each side. I went with 10 X15 wheels with 6 1/2 inch back space. I need to get 12 inch wheels with 7 1/2 inch back space though because the 10 inch wheels are really not wide enough to plant the tread flat on the ground.

[gomopar440]

Did you end up replacing the whole rear frame rail sections or just the horizontal part right under the trunk floor? You got me thinking about trying it that way on my other Challenger.

[tactransman]

If you look at the full trunk picture you can see where the weld is on both sides of the 2X3 square tubing by the wheel wells. That is where the frame starts to spread and get wider as it goes back. I made it come straight back. You will have to modify the bumper bracket bolt holes.On the front Mopar hanger kits you run a rod  that fits snug through the original leaf spring hanger and through the the hole in the Mopar kit hanger then weld the new hanger and then remove the old stock hanger. That way you don't change any mounting positions(as long as it was right from the factory) and your rear end is straight in the car.