72 340 Duster rear tires rub springs-what gives??

A customer upgraded from factory 14 inch big bolt pattern Ralleyes in the rear to 15X8 Ralleye repops he supplied and ordered from Summit.#56-5812042
He got the backspacing of 4.5".
In theory and on paper this should have worked on this car.
I sold him 2556015 Mickey Thompson's to help fill out the rear wheel well.
Not knowing the car's history or any other modifications,it is hard to say what else has been monkeyed with.
Don't get me wrong,this car is really nice and is a strong runner.
The car was upgraded by a previous owner with disc brakes up front and an unknown 8-1/4 rear axle.
Big bolt pattern all the way around.
At this point,I am only trusting the customer's judgement-it is his car after all and he bought it restored.
Even with the 255's the dang tires rub the leaf springs.
What gives??
Too much backspacing??
15X8 was ordered with the intent to go bigger in tire sizes or go slicks in the future.
I plan on measuring the axle width flange to flange and do a proper backspacing measurement with the wheels off.
I am also going to test fit some mounted cop wheels and Centerlines with 2756015 on them as well.
Ya think that after owning and driving the car for 6 years he would KNOW HIS CAR and HE SUPPLIED THE RIMS.
I really do not want to eat the damaged tires because of this and the measuring hopefully will save grace for me and my shop.
I feel bad about since he trusted my recommendations,plus the owner is a nice guy.

Neither he or anybody else can determine if the rear is a correct A body or a Dakota rear diff until I get the car back in the shop for a closer look.
I had seen many other Dusters with fatter tires and wide rims to a certain extent where no spring relocation or mini tubs were not needed--yet,LOL.
I have been around Mopars almost all my life and this has got me stumped.I never seen such a moderate size tire do that before.
Any help is greatly appreciated.
Thanks in advance.

yes something doesnt sound right with the total width of the rear end.
im running a 74 dart which is stock width of 52 5/8 " and i run 255/60/15 on a 4" back space and i have 1.5 " between the tire and the leaf spring .

Thanks.
I wrote down the stock width you mentioned.
Are your rims 15X7 or 15X8??

My friends duster has a stock width 8.75, springs NOT moved and stock tubs....cop car steels with 275 tires fit...

I had 15x8 chrome modular rims and 255 60 15 with no problems. I think the backspace was 3.5 or 4".

OT,, a side note do you have good prices on MT tires?

With 255 they shouldn't rub leafs, the rear is narrower than it should be if it were stock, he should have checked clearance there before driving car because you only need 1/4 inch clearance there, is he Shure its not rubbing the inner wheelwell? Even if you have more than 1/2 inch clearance with worn springs or bushings it will rub there.

In my experience this combo is the biggest that could be fit PERFECTLY on a 71 Demon with no spring or body modifications. Enough clearance for the tires inboard and outboard with room for growth and side wall flex, no rubbing anywhere.

Mickey Thompson 255 60R15 ET Street Drag Radials 27.00 dia.

Summit Racing 15 x 8 SBP Wheel (4.250 back spacing is the key) Code WVI-61-5754044

205 75R 14 on the front, also 27.00 dia

The cars stance with this combo is right on the money as well.

72 Duster here. Stock spring location. 8.25 out of 75 Dart. 15x8 Wheel Vintiques ralleys. 4.5 BS. 275/60s. Tires are very close to the springs and rub during sharp turns. A 4.25 BS would probably be ideal for my car but i don't think that offset is available in a 15x8 ralley. Did you bolt the wheels and tires on the car or did the customer take them home and put them on himself?

measure twice,buy expensive non returnable parts once.

This doesn't surprise me that they hit. I have a 74 duster with an 8.25" rear end in it. I am running 25560R15s on 15x7 chrysler imperial rims that have 4.5" offset. The tires hit the leaf springs. I have to run 1/4" spacers to make it work. I don't like the spacers but am am looking for other options. On my 1970 340 duster with an 8.75" rear I did the offset shackle and offset spring hanger thing from direct connection (this was years ago). Also the spring perches needed to be moved. This gave me clearance for 28" 10.5 goodyear slicks on 15x8 centerlines with 4 7/8" backspace.

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measure twice,buy expensive non returnable parts once.

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IIRC, the Wheel Vintiques repops were (are?) sold standard as 15x7. The 15x8's were special order and non-returnable. Hope this helps, they were throwing up the warning flag.