Going to 18" rims questions
Wanting to upgrade my '68 Barracuda to 18's since good quality 15's are getting rarer by the day.
It has a rebuilt stock front end, small ball joint spindles, SSBC 153 disc conversion, upgraded sway bar, with factory small block T-bars. Rear has a Strange S60 Dana rear with 11" drums, stock spring location, and sway bar.
I don't like the looks of most 17"/18" wheels. However, I did find some that are meant for suv/trucks and hoping I will be able to go with them. They are only offered in 18x8 but two different backspacing/offsets. One is 10mm offset with a 4.89" backspacing and the other is 35mm offset and 5.87" backspacing.
If I'm correct in my thinking, from all I have read on here, I think the 18x8 with 35mm offset and 5.87" backspacing version is what I need. Please correct me if I'm wrong!
Now, the even more confusing part to me is which size tires front and rear should I run. I'm hoping for sizes that are relatively easy to find at most tire places (this will be a daily driver) and hopefully not look like I'm riding on rubber bands. I know I gotta keep the front under 26" in height since I don't want to permanently modify the fenders if I don't have to. I'm thinking a 245/40 for the front. Rear I would like to have a little bigger tire to fill up the wheel well a bit but have no clue.
I know I still have to measure everything to know for sure but if I get the rim choice figured out I'll be able to figure out the most tire I can squeeze in on the rear. Any input pointing me in the right direction would be appreciated.
So with a Barracuda your biggest issue will be tire height and clearing the front lower corner of the fender. Keeping the tire height below 26" and using as much backspace as you can get away with will help that. An 18x8 with 5.87" of backspace shouldn't be a problem at all for a 245/40/18 up front with respect to everything other than the front lower corner. I know it will fit everywhere else, I just don't have a Barracuda and a 25.7" tall tire is pushing it based on what I've seen on the board anyway. Also, check the specs for the exact tire you want to run, because I have seen 245/40/18's spec'd as tall as 25.9", which probably won't be a good idea for a Barracuda if you don't want to modify anything.
In the back you'll probably need the the +10 offset if your S60 is A-body width. With the springs in the stock location an A-body 8 3/4 with BBP axles gives you about 6" from the face of the drum back to the springs. Does on my car anyway. But that's still not enough to run 5.87" of backspace because you need about a 1/2" of clearance and to account for probably about a 1/2" of tire overhanging the rim. So the 4.89" backspace should work, add that 1" and you'll get 5.89" so it will depend on the dimensions of your S60. That combo would clear the springs on my Dart.
And, don't base your tire sizes on anything other than 67-69 Barracuda's. In the front the lower fender corner is more limiting than any other 67+ A body. In the back, you can use the springs and inner tub as a reference, but the outer wheelhouse on a Barracuda is almost a full 1" larger than a Dart or Valiant. Like the Demons/Dusters/Dart sports the Barracuda's can get a 275 into the stock wheelhouse with the springs in the stock location, can't do that with a Dart.
Sorry, read that backwards at first time I replied. I don't think a 35mm offset with a 5.87" backspace will work.
You likely can't go any more than a 4.5" backspace on the rear and 4 - 4.5" backspace on the front of a stock suspension.
You only have 5.5" from the face of the drum to the leaf spring in the rear.
In the front, with the stock suspension and BBP brakes you can run-
~4.5" backspace with a 15" wheel (brakes and suspension limit the clearance)
~5.6" backspace with a 17" wheel (tie rod ends limit the clearance)
~6" backspace with an 18" wheel (with stock UCA's, the UCA itself at full steering lock and full suspension droop may be a limiting factor)
These are
approximate numbers, different rims sometimes have different hoop profiles, alignment and suspension settings can come into play as well as different brake packages. But with 18" rims the tie rod ends fit inside the hoop of the rim. The only interference I ever ran into with 18's was at full suspension droop and full steering lock, but that was with 18x9's with a 6.1" effective backspacing (they're +35 so technically 6.4" of backspace, but my brakes push the hub face out 5/16", so, 6.1").
In the back it totally depends on which axle you have. An 8 3/4" with BBP axles is about 6" from drum face to the stock springs give or take factory tolerances. A BBP 7.25" or 8.25" is a full 1" narrower, so you lose a 1/2" per side. SBP 7.25's are different again. And of course a SBP 8 3/4 is about 3/8" narrower per side than one with BBP axles. Depending on the axle AND the body style of the A-body you have you might want anywhere from 5.25" to 4" of backspace to center the wheel in the wheel well.
I'm thinking a 245/40 up front and possibly a 245/50 rear to help fill the wheel well a bit more height wise. I think it should be doable if I can get the backspacing right.
I agree, that should work. It will be close on the front lower corner of the fender in the front. In the back, you could run a larger tire if you wanted since you're not running the same front and rear already. A 255/45/18 would fit back there and will fit on those 18x8s with 4.89" backspacing (assuming your S60 is BBP A-body width). Just take that drum face to spring measurement to be sure. You could also use a small spacer if need be, because you have room for more tire to the outside.
