How much horizontal motion in the rear from cornering?

[bri-rock]

I'm trying to size my wheels and tires right now. I've read plenty of threads saying that I can manage to cram a 275 tire in the rear without mini-tubing. When I measure the available width available on my car to fit the tire in the wheel well, I get 11.5 inches (if I roll the fenders). With a 275 tire at 10.8 inches, that doesn't seem like a lot of clearance for any horizontal motion of the suspension. I've got 5-leaf springs back there with a Hellwig sway bar. How much horizontl motion can I expect? If the horizontal motion is too much, what would be an appropriate ride height so that the tire never sees the inside of the fender? Like most people on here, I want to be as low as I can with the largest contact patch. Any input is appreciated.

[CHRIZ28]

I think he's talking about the tire being pulled out of the wheel well, or being pushed into it depending on which way the turn is. I've seen pictures where it looked like the tire was being pulled an inch or so. Some other's don't hardly move at all. I figure it depends on tire construction, weight of the car, and suspension. I have no idea how to know what your car will have though.

Chris

[79-TA]

My Trans Am had a very slight rub in the rear. I think the rear end was moving over half an inch to either side. I used my favorite 4 pound clearancing tool to solve the problem.

[bri-rock]

That's gives me something to work with. Thanks, Brett.

[rustomatic]

The best thing I've recently done to the back end of my car is the Maier Racing adjustable Panhard bar. It's completely changed the behavior of my back end in turns (awesome!); it's also almost completely eliminated any sense of inner fender tire rub. It's a pretty easy install (minimal welding), but, oh, you don't have a Ford thing... If you can't find a long-ass adjustable panhard setup, I'd look into a Fays2 Watts link; it's the racer's choice...



For Panhard pics, try Googling the word Falcon in combination with Panhard or Watts link, or just Panhard or Watts link...

[aronhk_md]

Be careful and remember you are doing static measurements. If you are going around a corner the ouside suspension is going to be compressed. How much only you can measure. Only way I can think to do it is take toothpicks and some gum. Cut the toothpick and stick it to the underside of your fender pointing straight down. Play around and corner hard. Check if its still there standing straight down. If its moved or gone, shorten the toothpick and keep playing til you dont dislodge the toothpick.

Do this all with a set of smaller tires and wheels. When you figure how far your body rolls toward the tire it might give you some clue how far up in the wheel well it goes. Keep in mind that wider tires will have more grip and your body may lean even a bit more.

You could try doing the same thing on your spring or shackle with a toothpick sticking out horizontally toward the tire to see if you can measure the deflection.

Might take some big gobs of chewing gum......or maybe clay would work too? Maybe just clay by itself without the toothpick?

[neki67]

I'd look into a Fays2 Watts link; it's the racer's choice...

Haven't had any rubbing problems anymore and a far more stable rear since installing the Fays2 in my 67 Camaro. Also creates a nice place to hang fuel pump and Fuell Pressure regulator and filter onto!

Only real drawback: you either have to go for dumps from the mufflers (+ 6dB) or do some extensive fabwork to try and get tailpipes in.

[Norm Peterson]

I'm trying to size my wheels and tires right now. I've read plenty of threads saying that I can manage to cram a 275 tire in the rear without mini-tubing. When I measure the available width available on my car to fit the tire in the wheel well, I get 11.5 inches (if I roll the fenders). With a 275 tire at 10.8 inches

These are mostly thoughts and not numbers to hang your design hat on . . .

Keep in mind that the 10.8" is at best an approximate number. Actual tire section widths vary a little either way from there, and more importantly will vary along with the wheel width as the wheel goes either wider or narrower than the "measuring width" rim. On wheels that are an inch wider than measuring, that 10.8 becomes something like 11.2". The tighter the fit that you're shooting for, the more critical these "small effects" become.

There will be some lateral tire distortion during hard cornering, at least an inch at the contact patches when you're cornering hard. Less elsewhere around the tire, but still not zero. This distortion tends to be larger when the tires are mounted on wheels that are narrower than measuring width, so using relatively narrow wheels to avoid the 11.2" vs 10.8" issue above may not gain you anything at all as you drive.

Don't overlook the tire shape - some tires are more "square-shouldered" than others.

With a leaf spring suspension, the axle will move laterally as some fraction of however much lateral deflection happens at the shackles, and there's probably going to be a little bending in the leaves themselves (~1/16"?).

I doubt the Hellwig bar is going to help the lateral movement issue much. But a Panhard bar or Watts link set at the proper height to avoid conflicting with the leaves will.

One thing that may work in your favor is that the axle tries to shift toward the inside wheel, which means that it and the outboard tire is trying to move inward and away from the outside fender sheetmetal, which will be moving down due to body roll. Toward the inside of the wheel well is where the clearances will try to close up.

For the inboard wheel, the body roll is up creating a little more clearance and offsetting (somewhat) the axle shift that is toward the fender there.


Norm