I decided to upgrade the wheels and tires on my 70 Cuda. Examination of the archives here on Moparts showed that a mixed opinion on whether 275/60/15 would fit well in the stock wheelwells. I wanted to go with 15" rims and the most tire I could fit. I ended up doing something different from what I had seen before and wanted to share what I did in case it ends up providing value to someone else.


Careful measurements of the distance from the brake drum mounting surface to the leaf springs and the wheelwell fender lip showed that the fit with 15X8, 4.5BS and 275/60 would be real close but possible. Of course it was hard to know the exact shape of tire and were the point of least clearance would be. I decided to go with American Racing Torq Thrust IIs.

Once I mounted up the rims and tires on the back I found that I was not completely satisfied with the fitment. The tires did not make contact with anything, but with sufficient suspension compression (perhaps 2") the inner fender lip could make contact with the tire sidewall. Given that my car is mostly street driven, this was a concern to me. In addition, the appearance was also not quite what I was looking for. The tires stuck out a little bit, and were not fully tucked under the wheel wells. I know some run this exact setup and will say that the fit was OK, but to me it was not quite right.

Here, you can see that with enough suspension compression, that there will be contact.

Views of the fitment.

Another view...

The leaf springs on a Cuda are not parallel to the frame rails. With the 4.5" BS wheels in front of the axle there was 1.5" of clearance between the tire sidewall and the spring; behind the axle there was only 3/4" of clearance. Again I turned to the Moparts archives to see if there was clear consensus on how much clearance was needed to be safe. Unfortunately there were mixed opinions on this. In the end I decided that 1/4" of clearance behind the axle after going to 5" BS wheels was not going to be safe enough, again because it was a street car.

Some folks put B-body rears under an E-body to allow for more BS. I may consider that at some point as well, but if I did that I would go with a Dana, and there was no funds to undertake such a project at this time. The other option was to move the rear spring perches on the 8 3/4. That would violate my "nothing but bolt-ons rule", and besides, I was not up to welding, and didn't know anyone I would trust to do it either. I was stumped on how to make this work the way I wanted.

After pondering the dilemma for some time, I finally had an insight that lead to my current solution. There was plenty of leaf spring to tire sidewall clearance in front of the axle, and where I need the additional clearance was solely behind the axle. The wheelwell itself had more than adequate clearance for the 275/60/15. I realized that if I could pivot the leaf spring about the spring perch locating pin, then I might be able to use more backspace without having to cut off and re-weld the spring perches. Based on the stock E-body leaf spring dimensions (22" front segment, 35" rear segment), it appeared that if I moved the front eye of the spring OUT away from the centerline of the car by 1/2", then I would gain 1/4" of additional clearance behind the axle. If I could achieve that then I would have 1/2" total clearance between the spring and tire sidewall.

Moving the front spring segment towards the tire was a bit counterintuitive, but I was hoping that perhaps a front eye hanger from another body style would help. At that point I called the good doctor (DrDiff) to consult on the feasibility of what I was trying to do. He indicated that I could try to use his A-body 1/2" offset front hangers, mounted on the wrong side of the car to change the offset direction, and his E-body 1" offset rear hangers. The thinking was that there would be enough play in the arrangement to use the 1" offset instead of the 3/4" I had calculated. Cass told me that Use of the A-body front hanger required a 5/8" hole, but that was easy to accommodate. The other downside was that the A-body front hanger could not directly provide the stock E-body height; there were two holes for the spring bolt, and one would lower the car by 1/4" and the other would raise it by about 1" (if I remember what he told me correctly). I decided this was close enough to try!

The assemble was straight forward, and I decided to use the upper mounting hole for the eye of the spring. The axle perches easily set down on the locating pins. I could now see that the leaf spring was almost parallel to the centerline of the car. Measurements from the brake drum mounting surface confirmed that all was going to plan. I ordered up a set 5" BS custom offset 15 X 8 Torq Thrust IIs, which took about 4 weeks to come in. I then got the MT ET Street Radials moved from the previous rims to the new ones, and put them on the car. I was much more pleased with the appearance, and just recently put the car back down on the ground on 4 tires. The tires are now nicely located in the wheelwells, and the size is somewhat concealed.

Here is a similar view to compare against the 4.5" BS picture above.

Another view with 5" BS...

Oops, same picture...here is the one I intended.

I run 275/60/15's on a 70 Cuda with Torque Thrust wheels but I chose either 4.75 or 5" back space. Don't remember which. No contact.
I am thinking you must a good 1" tween tire and leaf-spring? I have about 3/4"

Edit after reading your post above. Yes the close spring contact area is the rear segments, I thought about intalling the rear offset hangers to gain clearance, but didn't have to for 275/60/15s. In fact, I think it may be possible to fit 295/50/15's with the offset hangers.

So now you are sitting on a set of barely used 4.5" BS TT's?

DrDiff reminded me to check the pinion angle after changing the height, and to my surprise it looks like I will be fine with use of a simple shim. I assembled everything with a 4 degree shim in place, because I was concerned that the upper mounting position would rotate the pinion too far up. However, I hadn't considered that in lowering the rear of the car, that was improving the down angle of the transmission output. Currently the car has the trans output at 4 degree down, and the pinion is 2 degree down, and I am considering changing the shim to a 2 degree shim but I think I will try it as is for now.

In conclusion, this approach allows a 5"Bs wheel to be easily used on an E-body without use of any cutting or welding. The only consequence is that the ride height will need to change some.

Two other interesting tidbit is the weight of the rims. The original AR TT-II rim in 15 X 8 with 4.5" BS weighed 16lbs. The custom 15 X 8 5" BS rim weighed close to 18lbs. This was more than I expected, but I certainly want a nice strong weld between the two halves. In addition, I didn't know up front that AR was not going to dress the weld in any way. At first, I was sort of upset by this, but with the wheels on the car, I can't really see the weld from the outside.

The full side view above gives a good idea of the new stance. Here is another side view of slightly better image quality.

Boy, I wish my car had that much clearance! With the 4.5"BS, I only had 3/4" clearance behind the axle. With the 5" BS, it would have only been 1/4", which I was not comfortable with. Now, with the 5" BS, I have 1/2" clearance.

Each car is likely different, and the tire will also affect it because the widest point of the tire can be a slightly different diameters from manufacturer to manufacturer.

Yes, I have two TT2 15 X 8, 4.5"BS that had tires mounted, and about 100 street miles. I am still debating on whether to hold them for another project or sell them.

Also, I don't think you can use the offset rear hangers with no change in the front hanger, without relocating the spring perch. That was something I was avoiding doing.

I had considered a 10" wide rim with the 275's, but on my car, there was no way to make that work since the wider rim increases the tire cross-section, which would have eliminated my spring to tire clearance and/or the tire to fender lip clearance depending on the backspace.

There was a post about this in the race section a few days ago. On my '73 cuda with stock suspension, I have the MT ET street radials 295-55-15 on a 15x8 rim,fits fine.

Nice post and good thinking, it's always good to see someone thinking of a new and simpler way to try and achieve something. I've read a LOT of posts on this issue over the years (E-Body tire clearance) and don't ever recall someone pivoting the leaf spring in the way you mention.

IIRC, most people have found they can accommodate 275 or some even 295 without alteration, but it is certainly true that it depends on a number of factors that might differ from car to car.
I'll put this on my list of options to consider when I actually come to spec and buy my wheels/tires - top of the list so far had been a Dr Diff relocation kit (rewelding perches) with stock axle.

Nice one and thanks for posting

Good info, I hope that this one is worthy of the archives for future reference!

Isn't the angularity of the springs (toe-in) done on purpose for handling reasons? I am wondering what effect, if any, there might be from this modification...

Yes, I'm sure there is a bit of variation from car to car. The other factor for me was the appearance. I know some folks are fine with the tire location in the wheelwell with the 4.5"BS wheels, but it wasn't quite what I was looking for.

Yes, I believe you are right; the factory angled the springs to assist with handling. There is likely some affect to straightening out the leaf springs, but I doubt it would be noticeable unless you were road racing. I believe all of the spring relocation kits try to put the springs parallel in order to maximize tire clearance, so what I did is no worse than those solutions.

Yes I did wonder about the factory rationale for the non-parallel springs - was it purely packaging or was there an advantage?

If there was a handling advantage then I'm guessing that it will be more than compensated for by the extra tread width. But it would be good to know.
(But agree that traditional relocation methods would have the same issue anyway)

That certainly is a new approach to fitting rubber. It seemed to be a bit intensive time wise and now with a custom backspace wheel, may not have been the cheapest, nor quickest, method to achive a bolt in fit, but I'm glad it worked for you.

The simpler bolt in method is to move the springs inboard 3/4 to 1 inch, then bolt in the B body rear. While the B body housing does not offer any more wheel well room than the E body housing, their ready availability does make it easier for most guys than cutting and rewelding the perches off the E body rear. However, either of these changes will alter the required backspace to fit the rims, especially since there is a difference in B body housing widths pre/post 67.

For my Challenger, the 3/4" spring move combined with a '67 B body housing allow a 15x10 with 5" backspace install that resulted in a 12" wide tire fitting with room to spare on both the spring and fender side. Entirely bolt in, using off the shelf parts.

BTW, the splayed spring design is a handling benefit that is designed in to all E bodies, post 72 B bodies, and all FJM bodies. E bodies are narrower at the front, while all other are narrower in the rear. What the splayed mount does is put the spring in a position that provides additional torsional resistance to the leaf, hence more roll resistance to the body, and minimizes roll steer by the rear housing moving and altering wheelbase length. The extra tread width doesn't contribute to either of these attributes.

I think the approach I took was an "intermediate cost" route. I considered using a B-body rear but if I went that route I didn't want to put an 8 3/4 back in. The cost of stepping up to a Dana was significant.

Even if using an 8 3/4, you still need the housing and axles from a B-body plus the front and rear hangers. The AR TT2 15 X 10 rims are actually more expensive (around $270) versus the custom offset 15 X 8 (around $250). From what I investigated, going to a B-body rear was going to be more expensive than what I did. Of course the extra expense would allow the fitment of even larger tires but for my car, 275/60 will be plenty.

I do agree that it took a good bit of time and labor to work this out. And I did end up with a set of rims which I didn't use. I can still recover some of that cost if I choose to sell them. It would have been easier if I had the idea in advance. I thought I would share this idea, since it might help someone else facing a similar situation.

I agree that it is not for everyone, but it may be worth considering. For me, it provided the "right" look for the car.

Thanks for the insights on the handling. I'll have to wait until the weather improves to see if I can notice any change in the roll stiffness of the car.

I just stuffed 325 50R 15 NITTO 555R's under my '70 'Cuda with 10 inch wide 5.5" backspaced Ralleys, a b-body rearend, Dr Diff's 1 inch inset hanger kit and Caltrac Monoleafs. It's tight, but nothing rubs through the whole range of travel,and I didn't have to roll the fenders. It fills the wheel well nicely.

...another view. I don't believe anything bigger will fit without rolling the fender and relocating the spring perches inboard a bit more with DrDiffs 1.5 inch kit. He says the rear valance may interference issues with that kit though. I guess I'll just have to get by with these for now.

...and from the front.

Wow! That sure is stuffed. Is this a street car? How much tire sidewall to inner fender lip clearance do you have on rear suspension compression?

jbc426, I am also curious to know if your car is street driven often and how the Caltrac setup affects the feel of the car on the street as well as the track.


This is a very informative thread. I am looking into improving my rear suspension and this information really helps.

holy cow, love the look of the 325's in there!!
more pics of you have any.....definitely a path I'd like to take on my AAR.
Thanks for all the info from all of you guys!

My Challenger with a 3/4" spring kit, 67 B body rear, 15x10 with 5" back space and a 26x10x15 tire. That measures out to about a 305r/50x15 in metric terms.

Love that stance and rake!

Thanks!

what you don't get a perspective of with that shot is how low the car sits. While I haven't measured it, I'd guess the top of the roof to be around 48-52".