[Nitebird]

On my 1979 Trans Am SE I have the Pro Touring F body solid aluminum bushings set at stock height. I also have the GT front springs on it. However I have 2 inch lowering blocks in the back with stock rear springs.

Whenever I go over bumps my rear suspension lets the tires (255/60/15) rub against the lip of the quarter panel and my exhaust hits the rear end as well when I go over bumps.

I wonder if the rear GT springs that are stiffer will control the rear alot better and not allow the tires to rub and prevent the exhaust from hitting as well?

I tried calling Pro Touring F body but their phone is not working as their message machine is full.

[HWYSTR455]

What wheels are you running? And tires?

3 things come to mind, first, you can roll the quarter lips. Second, you can use a tire with less sidewall 'bulge'. Lastly, you can run a wheel with more backspacing.

On the exhaust, I'm guessing you're talking about the U bend that goes over the tubes? Hits on the front side? You can take a BFH to it and dent it some for added clearance. I got almost 3/4" doing that.

But, to answer your question, a de-arched spring with a higher rate, yes, will prevent as much compression, and possibly eliminate the contact. Won't know unless you try, it's a trial and error thing.

.

[Nitebird]

Originally Posted by HWYSTR455

What wheels are you running? And tires?

3 things come to mind, first, you can roll the quarter lips. Second, you can use a tire with less sidewall 'bulge'. Lastly, you can run a wheel with more backspacing.

On the exhaust, I'm guessing you're talking about the U bend that goes over the tubes? Hits on the front side? You can take a BFH to it and dent it some for added clearance. I got almost 3/4" doing that.

But, to answer your question, a de-arched spring with a higher rate, yes, will prevent as much compression, and possibly eliminate the contact. Won't know unless you try, it's a trial and error thing.

.

I am running the factory stock Pontiac 15x8 snowflake WS6 wheels along with BF Goodrich radial TA 255/60/15 tires.

Alot of people run that wheel & tire combo but I did lower the rear 2 inches and the lip is about 1 1/4 inch above the tire.

And yes I am talking about the U bend that goes over the rear end that is hitting the rearend tube on left and right side exhaust U bends. I dont have any more adjustment to the mufflers either as they are very close to the floor board as it is. I may have to dent the exhaust.

[HWYSTR455]

Look at the specs for the tire you run attached.

Tread width is 9.1", and section width is 10.2". So that 'bulge' is 1.1" wider than what's touching the ground. And then there's squirm.

Rolling the lip gives you about 1/3" more clearance. If you're not comfortable with doing that yourself, a body shop can do it for a reasonable price.

Going to a tire with less section width usually means going to a different wheel, but lucky for you, the YO snowflakes are available, it's just a matter if you like them or not. Less sidewall means less section width, usually.

Yeah, on the U bend, it's not the up/down, it's the forward/back that would help. But in my case, with a 'traditional' dual exhaust (not crossover), I have the same problems with 2.5 tail pipes. You can also use a C clamp, and an impact gun, just put a piece of wood on the rear seat side so it dents the side of the axle tube.

You can always try the new leafs, can sell the originals, or the new ones if they end up not working. Raising it some obviously will help, but if it throws the stance or corner weights off, then it's a move in the wrong direction.

.

[HWYSTR455]

You might be able to go to a 50 series tire too, and keep everything else. Forgot to add that one.

EDIT: Or actually, a 245, that would give you .4" less in the section width.

Here's the complete listing for specs on the BFGs. Obviously, other tires vary too, but you would probably have to change a set.

https://www.tirerack.com/tires/tires...omCompare1=yes



.

[Mike Fowke]

FWIW, I have Global West L3 leafs, Hotchkis (Fox) shocks, a 1" lowering block, and the same wheel and size tire on my '78. I have about the same clearance between the tire and quarter, and I never get any contact with the tire or axle. I also have their front lowering springs and solid mounts. I bet adding the GT leafs would fix your problems.

A rear shock with less compression and a rear sway bar (or bigger one) might help. I ran Koni reds with the stock WS6 leafs. The overall spring rate felt about the same as the current set up, but the WS6 was stock height.

[78w72]

the ptfb rear leafs only lower it 1-1.5". so with stiffer springs & less lowering i would think that would elimintae your issues. a 255/60 on 15x8 snowflakes should easily fit. i had 275/60's on 15x8 snowflakes & the full gt kit, nothing was even close to rubbing.

[Nitebird]

Originally Posted by HWYSTR455

Look at the specs for the tire you run attached.

Tread width is 9.1", and section width is 10.2". So that 'bulge' is 1.1" wider than what's touching the ground. And then there's squirm.

Rolling the lip gives you about 1/3" more clearance. If you're not comfortable with doing that yourself, a body shop can do it for a reasonable price.

Going to a tire with less section width usually means going to a different wheel, but lucky for you, the YO snowflakes are available, it's just a matter if you like them or not. Less sidewall means less section width, usually.

Yeah, on the U bend, it's not the up/down, it's the forward/back that would help. But in my case, with a 'traditional' dual exhaust (not crossover), I have the same problems with 2.5 tail pipes. You can also use a C clamp, and an impact gun, just put a piece of wood on the rear seat side so it dents the side of the axle tube.

You can always try the new leafs, can sell the originals, or the new ones if they end up not working. Raising it some obviously will help, but if it throws the stance or corner weights off, then it's a move in the wrong direction.

.

I wonder if everybody who lowered their cars about 2 inches had to roll their fender lips when running 255/60/15 tires.

[HWYSTR455]

I honestly don't know, but at one point I was going for the most meat I could possibly fit without mini tubs, and rolled mine early on.

I also slightly narrowed my rear, have posted the dimensions here before. Did that when I went to disc brakes, and to get in a range of popular backspacing on wheels. Also ensured the housing was centered. Way it is now, I can go to a 295/305, depending on the brand tire.

That tire sidewall bulge works against you on the inside too, it can contact the leaf, and you have to allow for enough space for tire squirm.

I use the GW leafs too, there is no substitute. They are hands down the best leafs out there, but you pay for it too.

.

[HWYSTR455]

My stuff is slammed, but measuring the rear isn't going to help until I have all the parts in the car, and a full tank.

.

[Blued and Painted]

Glad to see 15" TA radials are available again. Time to start price shopping.

[78w72]

Originally Posted by Nitebird

I wonder if everybody who lowered their cars about 2 inches had to roll their fender lips when running 255/60/15 tires.

i didnt have to roll the lip or hammer the seatbelt bulge at all.... 275/60 BFG.

[78w72]

Originally Posted by Blued and Painted

Glad to see 15" TA radials are available again. Time to start price shopping.

again? 15" TA radials have always been available in the popular 15" 60 & 70 series sizes...