The 68 Barracudas have huge rear wheelhouses, that I personally have fit up to 325/50-15s into. Yes into, and dropped the car back close to factory ride height or a lil lower. However, most of the time, she is running 295s.
I had started with 235fronts and 245rears, (both 14s) with a P-valve from a 73>75 Dart. But the 245s were a poor match to my 367. There were a lot of unscheduled spin-outs. So Next up were a used pair of 275/50-15s , which were not much better.
Next up were another pair of used tires, this time 275/60-15s. Meh, they were used and already hard, so again, I just burned thru them. But I did notice with these, that I tended not to spin out as frequently.
Finally I had had enough.
I moved the springs and narrowed the rear, to put on the 295s. That was a hit! These now made controlling the rear end waaaay easier, and no more wipe-outs.
The 325s I made fit, just to parade around with at the car shows, and to run a few trips down the track with.
Most of these tires are so much bigger than the factory tires (D78s IIRC), that the factory proportioning don't mean a thing.
I decided to explore that, by gutting the P-valve, and she now runs equal line pressure front and back.
On the front are the capable KH 4-pots.
The rear now has 10" brakes and I swapped out the rear Wheel cylinders several times, for each tire size; so, not sure what is back there today, might be 1 inchers.
I swapped out the big M/C for a 15/16th which I much prefer the feel of. and I run a big F-body-type booster.
So, I can tell you this;
when I stomp the brake pedal now, it's like I imagine throwing out parachute would feel like, after jumping out of a plane; and with very little front-end dive. and the car now wears out rear shoes between 2 and 3 times as often as the fronts. and no, there is ZERO tendency for the rear to come around. I can stomp the pedal in mid-turn with confidence.
What's my point?
1) Well, what size street tires are you planning to run? That's gonna help you make these decisions, and if you ever change rear tire sizes, I highly recommend to revisit your brake-bias.
2) if yur installing a 360, I highly recommend at least 275/60-15s. else it will be very difficult to keep the back in the back, especially with a 750 DP carb, unless maybe you have an early-shifting automatic with a very low stall. ...... but who does that, lol.
3) if you have a 318, well for the most part, they will never have a preponderance of torque, so you may get away with less tire, and that means, less rear brake, unless you manage to have a lotta front brake, which will require more than 235s, which will require you to massage the fenders and or, cut them to make room for turning.
On the street, I find 235/60-14s to be adequate with the 295/50-15s; they seem to be a pretty good match for eachother.
Whatever,
Happy HotRodding.
