I think I'm pretty well settled (FINALLY!) on the tire and rim size for my 70 Challenger. The car has a stock E body rear axle. When purchased, the car had 245/60/14's on stock Rallye 14x7 rims all around, a 14" spare, and power drums on all 4 corners. The front control arms and rear leaf spring are staying stock. The "pretty well" qualifier is added because they're still a couple of questions below about how these choices might limit future upgrades. I'm keeping the rear drum brakes (11X3) for now and have changed the front to disc with a basic kit from Right Stuff. While I like having the look of the 17" front / 18" rear, the practical side of me has the choice heading towards using the 17X9 wheels with 5" backspace and 275/40/17 tires on all 4 corners that 72bluonblu is using. I like the ability to rotate the tires around all 4 locations to keep tire wear relatively even, and in a pinch can put the existing spare to work (flat front tire means moving a rear tire to the flat location, then the 14" spare goes on the rear). If I've done the math right, the 275s will be just a little taller than the 245s on the car now (25.7" versus 25.4").
So here are the questions assuming that the 275/40/17s on 17x9s with 5" bs are on the car, keeping in mind that I'd like to avoid having to roll or trim any fenders or remove any internal bracing:
1. Will using 275/40/17s with 17x9s on the front limit my option to use 2" drop spindles at some point in the future?
2. Along the same lines, would there be any fitment issue with dropping the rear axle an inch with blocks if that's something that interests me later?
3. Will there be enough space on the back to upgrade the drums to disc brakes if that's in the future?
BTW, thanks to all the folks that have been posting their wheel/tire info on this thread. It's a lot to read through, but all of the info minimizes the risk of an "oh shXt" moment later for those of us going through this for the first time.
The decision about buying American Racing Torq Thrust II or Cragar S/S wheels will come later.
1. No, I ran 2" drop spindles briefly with my 17x9's. BUT, you don't need drop spindles. If you increase the diameter of the torsion bars enough you can lower the car more than is practical to drive on the street. All you have to do is match the amount of travel the torsion bars use to the amount of travel available at a given ride height. The larger the torsion bar, the less travel that is needed. With the 1.12" torsion bars on my Challenger I was able to lower the car with the torsion bar adjusters to the point that it was just as low as it was with the 2" drop spindles. I actually raised the car up a 1/4" from where I had it because I got tired of dragging things on speed bumps and driveways. Drop spindles cost more money than torsion bars, for the price of most of them now you can get larger torsion bars and good shocks to go with them. Not only will the car "look cool" with the lower stance, it will actually handle better too. The suspension geometry is better without the drop spindles as well.
-also, you mentioned you're running Right Stuff brakes up front. The 17x9 with 5" of backspace is figured for the 73+ Mopar disks. Different brake kits can change the track width, and I don't know what the Right Stuff brakes do as far as changing the track. The Right Stuff brakes appear to just be aftermarket supplied Mopar disks, but I could be wrong on that.
2. Shouldn't be, assuming that your backspacing is correct and the 275's are centered in the wheel wells. The 17x9" with 5" of backspacing should be close with the stock E-body rear and stock spring locations, but remember that I actually run a 68-70 B-body rear and a 1" spring offset. I have a TON
of extra room. I know that 275's will fit on cars with the stock rear and spring locations, but, what I'm saying is measure your car to make sure that backspace will work for you. It should be pretty close, but all these cars are a little different and if you're making it that tight the body tolerances matter. If you do the 1" spring offset you'll want more backspace than 5" with the E-body rear to take advantage of the extra space inboard.
3. Depends on how your backspacing works out. Disks usually add a 1/4" to 5/16" per side, so, you'll need that much "extra" room to the quarter. If your goal is not to buy new rims when you upgrade you'll want to set your backspacing to put your wheels as close the springs as possible with the drum set up, otherwise you might not have the extra room.