tire size fitment on Challenger

[Lotsapins]

I'm currently having wheel woes. I got a set of AR Hopsters with the car and they don't clear good in the front. On a hard turn, if the front drops it will rub the fender lip up in the higher part of the fender. That could end up bending the fender out and causing some damage. Nearest I can figure the wheels are 16 X 8 with a 4" backspacing. Tires are 225-55-16.
I am looking at a set of Foose Legends with these specs.
18x7 4"backspacing and 224-45-18 front
18x9  5"backspacing  and  255-45-18 rear
This is what the tire place recommends, but I want to be sure.
It's a 70 Challenger Convert with stock rear springs that are not holding the rear up any extra. I have the front end cranked up and the rear with air shocks to compensate for the front. I'd like to put stock shocks back on the rear and drop the front with a slight rake (say 3/4 to 1").
Any thoughts or suggestions? Will the tire package I'm looking at accomplish the goal?

[HP2]

They will fit but might have the same interference issues you have now. You are using the same width tire. The drop in aspect ratio offsets the change in wheel diameter so the overall diameter of the package won't change much, if at all. The 1" Narrower rim may pull the tire in an extra quarter inch per side I'm guessing, so you aren't significantly narrowing the overall combo while still retaining a 4" backspace on the new rim. I would go with a 4.5 to 5 backspace for the front tires as well to avoid fender lip interference. With a 16" or 18" wheel, you can get a 5" backspace in there without interfering with any components.

[Lotsapins]

I cant get the wheels with the 4.5 inch backspace. They don't make them in 18 x 7. The tire dealer guarantees fit and no rub problems. Guess I'll try them and hold him to his word if there is a problem.

[Bucks70RT]

From what I have learned from others on this board is your offset on current wheels is wrong. By your spec you have a -12 offset. you should have 0 to +8. Offset is the key to wheel and tire fitment. With your negative offset it pushes the tire too close to the fender. A 7" wheel should have 4" to 4-1/4" back space. That's 0 to +8 offset. I run a 265/40-18 on 9" wheels with +7 offset in front and back. That is 5-1/4" back space. I have not had any rubbing problems. I have stock dimensions on suspension.

[Bucks70RT]

oops. 8" wheel should be 4.5" to 4-3/4" back space. your 8" wheels with 4' back space are -12 offset.

[Katfish]

Agreed, you need 4.5" back space

[72bluNblu]

I replied to your post in the wheels and tires thread with some more detail.

Before you do anything, you need a new alignment. The numbers you posted in your other thread are way off.

In fact, your current wheels should clear with the proper alignment. I have 275/40/17's on all 4 corners of my Challenger, on 17x9" rims with 5" of backspace. With those specs, my front wheels stick out an extra 1/2" further than yours, and mine don't rub. They're even the same height as your current tires. The only difference is the alignment. Well, and my 1.12" torsion bars. But still, I should have a full 1/2" less fender clearance than you. On top of that, my car sits quite a bit lower.

Fix your alignment first, then see if you still need new wheels. -.5* camber, +3* caster, 1/16" to 1/8" toe in.

[Lotsapins]

I replied to your post in the wheels and tires thread with some more detail.

Before you do anything, you need a new alignment. The numbers you posted in your other thread are way off.

In fact, your current wheels should clear with the proper alignment. I have 275/40/17's on all 4 corners of my Challenger, on 17x9" rims with 5" of backspace. With those specs, my front wheels stick out an extra 1/2" further than yours, and mine don't rub. They're even the same height as your current tires. The only difference is the alignment. Well, and my 1.12" torsion bars. But still, I should have a full 1/2" less fender clearance than you. On top of that, my car sits quite a bit lower.

Fix your alignment first, then see if you still need new wheels. -.5* camber, +3* caster, 1/16" to 1/8" toe in.

Pretty much what they had told me at the alignment shop was with the front end so high, they can't get any more caster. The adjustment cams are all the way to their limits. So that being said the spec sheet has the caster in the red. I have bought the 18" wheels and tires and expect them in a few days. I will be taking the alignment numbers you gave and will have it realigned to those specs. I will get the ride height set to what I like and then have them do it. Just a quick question.. When yo showed the caster and camber specs, is it the same for both sides? and it the toe the total toe or is it per side. My guess is total, but I want to be sure. Thanks for the help and I'll be looking forward to the  new feel.   

[72bluNblu]

Pretty much what they had told me at the alignment shop was with the front end so high, they can't get any more caster. The adjustment cams are all the way to their limits. So that being said the spec sheet has the caster in the red. I have bought the 18" wheels and tires and expect them in a few days. I will be taking the alignment numbers you gave and will have it realigned to those specs. I will get the ride height set to what I like and then have them do it. Just a quick question.. When yo showed the caster and camber specs, is it the same for both sides? and it the toe the total toe or is it per side. My guess is total, but I want to be sure. Thanks for the help and I'll be looking forward to the  new feel.   

Huh. Your car must be sitting higher in the front than it looks.

Yes, the specs I listed are basically the same for both sides. You can run some cross-caster if the roads you drive are significantly crowned, but I wouldn't make it more than .5*. The 1/16" to 1/8" toe-in is the total toe.

Also, there's no reason to stop at +3* caster if you have power steering. The more +caster you run the more stable the car will be. Most modern cars run +7* or more, but if your UCA's have the stock bushings you won't likely get more than +3*. If you go to the Moog 7103 offset bushings or tubular UCA's you might get more. If you have manual steering you probably won't want to go more than +3* caster as it gets hard to steer.

I run my Challenger at -.9* camber, +5* caster, and 1/16" toe-in. But I have Hotchkis UCA's on it.

[Grec]

@72bluNblu

I'll note that your car does not have the wheel well trim, which the original poster's car does.

I know that on my car, the stainless trim sticks into the fenderwell further than the lip of the actual fender.

I don't have my car in front of me, but as I recall it was at least 1/4" difference... Not a huge amount, but still... when you're talking tight clearances, could be the difference between rubbing and not.

I had to slightly roll my trim in a spot or two to stop a rub I was getting on full turn

 

[Lotsapins]

If you have manual steering you probably won't want to go more than +3* caster as it gets hard to steer.


[/quote]

It is a power steering car. This car is for sale, but I drive it for personal enjoyment till it sells. With the new wheels, it should clear and be able to sit lower. That will also give me a shot at the different alignment specs shown above. I also have found that I only have these rub issues when the car has the wheels cut all the way and one of the front corners dips down hard. This was a 318 car and I think it has the 318 torsion bars still under it. With the weight of the 440 and a/c I am probably dipping down harder than it should. I will probably try to find some bigger torsion bars for a 440 and stiffen the front up. I don't know what size or part number to use, so if anyone has this info it would be of great help. I should be able to get some + caster with it lowered in the front and with bigger torsion bars and the tire change, I believe it will all come into place.

[Lotsapins]

New wheels and tires on now. Also changed to 780-781 torsion bars (440 & Hemi). Just have to wait till next week to get the alignment right, but it looks like it should be ok. Front end is stiffer now also.

[Lotsapins]

Got it re-aligned today. Here is the new specs.
LF Camber -0.5*
RF Camber -0.7*
LF Caster 2.6*
RF Caster 2.3*
LF Toe 0.17*
RF Toe 0.16*
Total Toe 0.33*

It does drive better and after the torsion bars were changed, my specs were a mile off. They didn't charge me again
although they could have since I had altered the height and changed the torsion bars.
I will drive it some more this weekend, but I think it's good.