[stevemopar30]

I currently have 14x8.5 rims and 235/60r14's tires in back. I want to go to a 15 inch wheel and want the widest possible rim and/or tire for the "beefy" look. Does anyone know the widest rim and tire I can go with and what the backspace would be??

[Hans]

I have 15x8 rims with 265/50/15 tires in the back but when I drive over a bump in the road the wheels hit the fenders...as I have high jackers in the back that's no problem for me, but I don't know what kind of that you have. I don't know how it would be if the car is stock.

[dave-r]

A 15x8 with 265 or even 275 tires will fit under the rear arches but you need to get the offset right. Your best bet is to get under with a tape measure but I think a 4.5 inch backspace is enough.
I do not think you will need to cut the wheel arch lip either.

Measure it yourself first though!

As far as handling goes. A 275 is at the limit of what you can fit on an 8" rim.

Hans. Yours must not have enough back space on the wheels.

I tried my 295/50/15 rubber on an 8" wide wheel and I had just a quarter inch between the rear leaf spring and the tire wall and the wheel arch lip needed cutting off. The tire looked far too wide for the wheel though.

I then went to a 10" wide wheel with 5.5" rear spacing and the tire was a better fit on the wheel but the tire wall was now hard up against the spring.

That was when I decided to move the rear springs in by 3/4" each side.

[mike]

Will a 15x8 rallye wheel with 4.5" backspace and 15 60 275 tire fit under the wheelwell of a 70 challenger without cutting at all. I'd like to know absolutely for sure since I will be mailordering this. Also, where can I get the correct trim ring for this? All I see available is a 7".

[Mike]

How difficult was it to move the rear springs to accomodate 10" rallyes. Were there any other mods besides that? Also, where did you get the trim rings to fit?

[Mike]

Does anyone know what 17" wheel/tire combo will fit under wheelwells without cutting the lip? Still would like to have a nice deep dish and have the height of a 15 60 275 rear tire.

[dave-r]

It will be a tight fit mike. I have seen 275s on 7" wheels that looked kike they fit ok without cutting the lip but it will be a close call and I can't tell you for sure if the 8" whell will clear it.

You can only get trim rings to fit 7" wheels. You can use these but you have a gap at the back (see my car).

Moving the rear springs involves a little fabrication and welding.

[dave-r]

I have a bit more time now so I will go into more detail on a couple of points.

When I said a 275 tire could fit under the rear arches on a 8" wheel I was talking about a 50 series tire and I think it will fit - just - but you will need to get under and measure things yourself to be sure.

To work out the tire diameter use the Excel spreadsheet on my web page. Putting in the 275x15x60 size it comes up with 28" diameter which is quite big. If you change the wheel size to 17" on the spreadsheet you will see that you need a 50 series tire to get about the same diameter.

To move the rear springs in 3/4" each side I used offset spring hangers. MP make hangers for this purpose but the E-body offset front hangers are for use with the shorter Super Stock springs which are A-body size.

So to do this on a Challenger with normal length springs you need to use A-body front spring mounts. The hole for the E-body spring bolt is in the wrong place though so you have to weld it up and drill new holes. I drilled three to give me some adjustment of the rear spring height which was a bit of a brain wave that came in handy later.

The MP offset rear e-body hangers are a simple swap from the original ones.

Then you have to cut off the original axle mounts and weld new ones in the correct position. I bolted everything up first checking that the axle was centered and adjusted the pinion angle before welding the axle mounts in place.

[Joel]

Dave, I don't have a clue to things when it comes to tire sizes and terms. I know, I know, I SHOULD know these things, but I don't. Could you tell me what the three digit and two digit numbers on the sidewall of the tire means. Dave, why did you have to weld the new axle mounts in the correct position twice. Also, do you have any pictures of when you made these suspension mods, before, during, and after?

[Mike]

Hey Dave, thanks for the info. I'm going with a 275 60 15 because of the 4:11 gears in the rear. That size tire is what I have right now but they are on reverse offset wheels so the car's ridin' high and I need to get it low. The tall tire size supposedly lowers my rpm especially on the freeway. I don't want to change the gears because the combo of 4:11's and a 440 big block is a great rush. Any suggestions? I do like the 17 or 18 inch look of torq thrust's but would settle for a deep dish look rallye without mods. I really want to clear a tall tire in the rear without cutting the wheelwells or doing the spring mods.

[dave-r]

Joel.
The three digit number is the width of the whole tread in mm. One of the other numbers is the wheel size i.e. 14" or 15". The other two digit number is the aspect ratio of the tyre. Or if you like it is the hight of the sidewall. This is described as a percentage of the width of a tyre. So a 60 series tyre has a side wall height that is 60% of the width of the tyre. A very low profile tyre would have an aspect ratio of 35 or 40 which would be 35% or 40% of the tyre width.

No you only have to weld once but you have to make bloody sure it is right first! I don't have photos either.

[dave-r]

Mike.
By changing the tyre height you are changing your final gear just the same as swapping gears in your axle. So to say the car is a blast with 4.10 gears and 275/60s is exactly the same as using 275/50 with 3.91 gears (within a couple of mph). I think you will just have to measure carefully and cross your fingers. If you want 17" wheels with 40 series tyres you should change the gears in your axle to something less wild or you will have no top speed at all.

[Joel]

Thank you Dave. I knew that the two digit numder had to do something with the percentage of the tire itself, something more like the percentage of how much of the tire is touching the ground. Yeah, I have tall tires on my car now. With the combination of 2.76 gears and the height of a 70 series tire, I won't have a lot of initial acceleration, but have alot more top end.

[Joel]

Dave, I looked at my Mopar Performance catalog and the MP website, but there is no mention of rear offset E-body hangers. I am a bit confused.

This thread has been very handy because these are some of the future changes and additions that I will make to my car. I want to get all the details correct before I take on the the actual project so I won't run into too many unexpected time delaying problems. Everybody knows that a car that is down longer than need be, is no fun.

[dave-r]

P4120076 is the part number I have for the rear shackles but my MP book is older than you!

[Joel]

It has to be over 21 years old, Dave! Thinking about ordering a new catalog?

The part that has the closest number to that in the suspension section is P4120077 rear spring FRONT hanger sets for A-body. From what you said, you ordered a OE E-body rear spring rear hanger bracket and a A-body offset rear spring front hanger bracket for normal springs, yes? If MP does not carry OE E-body rear spring rear hanger bracket sets anymore, where can I get a high quality reproduction set of rear spring rear hanger bracket sets?

[dave-r]

Just looked at the date on my MP book and it is not as old as I thought. Just 10 years old. Almost new!

I ordered my offset shackles just three years ago so even if MP have stopped making them a large outlet might still have some.

The PNs I have are;
P4120075 for A-Body and P4120076 for E-body.

Front hangers are;
P4120078 for E-body (but only if you use the shorter SS springs) and P4120077 for A-body which you can modify to use on your Challenger with standard length springs.

[Joel]

Thank you very much Dave. I will stick to the regular rear springs, thank you. I want to kept the suspension with some ride in it, meaning I want to have a some what smooth ride but to have as much rigidity as possible without loosing the ride quality that I enjoyed so much. I will keep in touch with you about the subject. Thanks again!

[Tim Ellison (Tim)]

Dave,

Did you get much wheelspin off the line when you were running low 12's? I was thinking of going to Hoosiers, as my current 60ft times are measured in seasons, but you're running 2 seconds quicker than me on BFG street Radials. I can fit 295x15x50's under no problem with my snazzy Bedford CF arches, and the rear gearing would be near identical to the existing Kelly's.
Plus, BFG's are about 1/3rd the price of Hoosiers.

[Dave-R (Roppa440)]

Here is the best timing slip for the car on BFG Radial T/As;

60ft = 2.020
330ft = 5.270
1/8et = 7.938
1/8mph = 91.98
3/16et = 10.178
1/4et = 12.206
1/4mph = 112.17

As you can see it is not a great 60ft time so yes I guess the wheels were spinning. But not as much as during the 13.7 I ran at York where the wheels were still smoking at the 1/8th mile mark!

[Tim Ellison (Tim)]

My 60ft times were in the 2.4- 2.7 second range, so that would be a decided improvement. I know torque/ horsepower and suspension set- up need to be factored in, but it's a step in the right direction. Did you drop your pressures much?

[Dave-R (Roppa440)]

Not at all. In fact normal street radials often grip better with higher pressure up (to a point). I think on that day I was using 30 psi.

[Tim Ellison (Tim)]

Thanks Dave.

2.0 seconds is going some for 'streets'. You must have weight transfer well sussed. Gives me something to aspire to.

[Dave-R (Roppa440)]

I have also got a fair amount of power on tap (on a good day!) and i am pretty sure that helps a fair bit too!

[Tim Ellison (Tim)]

Aha!
I knew you fella's were holding out on me.

[Tim Ellison (Tim)]

just looking to confirm some details before I fork out on a set of shiny new wheels:-

Bolt spacing should be 4.5 circle, front and back?

For the rears, I'm keeping my scabby old Kelly Supercharger N50's (295 x 50) for now, but looking to fit either 10 x 15 wheels with a 4.25 backspace, or 8 x15 wheels with a 4.5 backspace. I dont have to worry about tyre clearance against the outer arch lip (nasty glass arches), but I need to make sure they clear the leaf springs.
I'm going for 15 x 7's on the front.

What I don't know is:-

What is the correct backspacing for the front wheels?
What is the correct size/ type of wheelnuts? I have a collection of odd- sized rusty ones on at the minute, and want to get some new spangly chrome ones.

Help, guidance and opinions gratefully received.

[Dave-R (Roppa440)]

Bolt spacing is 4.5 yes.

The safest way to do this is to measure the back spacing and width on the wheels you have now and then get under the car with a tape measure and SEE how much you can go and in what direction.

I feel an 8 inch wide wheel is too narrow for a 295 tire. If you go to 10 inch wide I think you will be very close to the spring with a 4.5 backspace but without seeing that make tire on the wheel I can't make a judgement on how close it will be. My guess is it will be OK. A 4.25 backspace would be safe for sure but then you will be right out under where the stock wheel arches were. That may be OK for you but, again, without seeing your car or it's modified arches I can't tell for sure.

The wheel studs are half inch wide I think? The thread will be UNF. Don't you have anything to measure with?

Get yourself under there with a tape measure lad. Then if it works out wrong you can't blame me!

[Tim Ellison (Tim)]

Hi Dave,

In a masterstroke of forward planning, the car's currently at my brother's bodyshop having some welding done. He's gone on holiday, and locked the car safely inside. Otherwise I would have been underneath with my junior geometry set and have it all figured out by now. Ahem!

Having thought about what you've said, I'm inclined to go the 8x 15 with 275's route (4.25 backspacing). It'll fit under the car, and I can lose the arches, plus picking up on a comment made elsewhere on the MB, going to a smaller tyre width but using new tyre technology may yield better 60ft times. While I'm under there, it's probably a good time to replace the the leaky old air shocks with some gas adjustable units. Summit do a set at low prices. This will also hopefully help the rear plant a bit better.

To balance up the handling, I'm thinking 215's on the front to replace the current 185's. I don't think the extra weight will make a signicant difference in ET's, but I may be able to go round corners faster than 15mph.

[Dave-R (Roppa440)]

Sounds like a good plan to me.