Offset kit allows a 10.5" section width tire.
On a Dart that may be true, but a Duster it's
not. You can fit a 12" section width tire on a Duster/Demon/Dart Sport using a 1/2" spring offset if you do a little trimming on the quarter lip (1/2" or less). The Dart body style loses a full 1" of wheel clearance compared to the Sport body cars (Barracuda's too). I have 295's on my Duster on 18x10's, just a 1/2" offset and a little trimming. No relocation, no mini-tub, with an offset and a little trim I have just over 13" from spring to quarter. Plenty of room for a 12" section, especially with 18's and the shorter sidewall they bring.
My goal is the fit a 295 tire under my 72 Duster with 68-70 Body rear with springs relocated an trim wheel wells an a deep offset wheel(6.5-7 inches)I've been researching as much as I can an seems that I need a 68-70 B body rear but came across a super nice earlier b-body that was in a 70 charger but turned out to measure narrower than 68-70 specs at 54 1/4 ... My question is whats the widest tire you have been able to fit with the 5/8 difference?.... I was trying to get away with spacers but should I be concerned if I have to use a spacer alittle over 1/4 inch ?
You can still fit a 295 in there, you just need to adjust the backspacing to match the new width of the rear axle, that's all. The space between the offset springs quarter lip doesn't change any, only the width of the wheel mounting surface. The 68-70 B body 8 3/4 rear axle is 60 1/8" wheel mount to wheel mount, the 65-67 B-body 8 3/4 rear end is 59 1/2". The 54 1/4" measurement it just the bare housing.
Anyway, that 5/8" difference is for the whole axle, you're dividing it between two wheels, so, all you need to do is knock 5/16" off your backspacing compared to a 68-70 B body rear. If you're working in offset, it's 8mm. So, on my Duster I run 18x10's with 38mm of offset (7" of backspace) and 295/35/18's with a 1/2" spring offset and about a 1/2" trimmed off the quarter lip. That's with a 68-70 B 8 3/4.
If I wanted to use a 65-67 B 8 3/4, I would just need 18x10's with a 30mm offset, the backspace would be 6-11/16" (ish
), that would put the wheels exactly where they are now. All of these cars are a little different, on mine I have
zero extra room to my springs and a little bit to the quarters with the flange trimmed back. So I would be looking for an 18x10 with 27-30 mm of offset (6.6-6.7" of backspace) if I didn't want to run a spacer.
Spacers aren't that big of a deal, I try to keep them at a 1/4" thick or less just because you generally need longer wheel studs once the spacer gets that thick. But really a 5/16" spacer isn't a big deal either as long as you have proper thread engagement on the lug nuts. Which means you could run the same exact rims as you would have on a 68-70 B rear and just run a 5/16" (or 8mm) spacer. Heck that might even come in handy if you switch to rear disk brakes later, they widen the track width about that much.
And just in case you were to find an A-body 8 3/4, if you do the 1/2" offset and BBP axles you'd be looking for 18x10's with about 8mm of offset (5.8" of backspace). Give or take a few mm or a couple tenths.
