Bulitt

Well I have an 08 Z51 with the Pfadt bushings. Following a Z06 today at VIR I am still experiencing too much body roll compared to how flat he was. My car has been lowered @ 3/4" all around. I was only running 30 lbs cold in the tires so I think going up to @34 cold will help.
Do the run flats make that big a diff in side wall deflection? Will a shock upgrade like Bilstein's help with this issue???

burners

Body roll has everything to do with spring rates and sway bars (relative to cornering force). So you won't roll very much if you reduce the traction enough to avoid generating enough lateral G to lean the car. I don't think you want that. You are going to need bigger sway bars and/or stiffer springs. At least those are the things that you can change the easiest.

95jersey

yep what he said...bigger sways are the cheapest upgrade that will help, but bottom line is stock springs even Z06 are too soft for serious track duty

Black C5 Z06

Yeah. And if you're going to change shocks and springs, might as well go ahead and get coilovers

LS3FORME

hypercoil springs front and rear for track use 1100

pfadt coil overs 1700

pfadt sway bar kit. 900

gm T1 kit?

The pfadt can be use without the leaf springs.
The lgs' can be use without the leaf springs? Price.
Penske are like 3000 plus.

I would think the adjustable hypercoil track springs would be the cheapest bang for the buck.

Some one should do a suspension setup matrix.

gkmccready

Nobody makes "adjustable" springs so far as I know.

I love my HardbarUSA Dual-rate Penske coil overs. With the Hardbar set up it really doesn't seem like I need to move away from my stock swaybars. I have Pfadt Pfatty swaybars and pillow blocks in the garage that I tried earlier before going coilover -- they are nice pieces.

Remember, just changing springs will leave you unbalanced as the shocks won't be valved for the new spring rates...

Jahan

Someone more familiar with your suspension geometry should chime in, but lowering the car may have negatively affected your roll centers, either their static position, or how they migrate during cornering. You might be able to improve the problem just by optimizing your ride height.

Also, I'm not sure what bushings you are referring to . . . just the swaybar bushings? Or a complete set? Either way, stiffer bushings can quicken the steering response, which introduces higher lateral momentum and inertia, which in turn increases bod roll for a given suspension set-up. Increasing your roll stiffness will help too. Bigger bars is the easiest way to do this without negatively affecting too many other attributes.

rustyguns

LS3FORME

http://www.vansteel.com/index.cfm?fu...&SubGroup=1951

Adjustable race springs, not shock tube springs, but the cross leaf springs, with height adjustment.

ghoffman

OK, very, very simplified math model, with many assumptions but illustrate the basics. The body roll is generated by a moment arm (torque) that is from the CG to the roll center. The acceleration vector (sideways force) acts through the CG and the bigger the acceleration vector (i.e. more tire grip) the more "body roll moment" you will have. So, to put some rough numbers on this lets assume you can pull 1 g with your tires and the car is 3000 lbs and the moment arm is a foot (probably not, but the math is easy for this example) this gives you 3000 Ft/lbs of torque that is making the body "roll". Now, since the car is like 6 feet wide, and the moment arm here is 1/2 of that or 3 feet, you have 1000 pounds of force that has to be reacted in something, or here it is the 2 wheels on 1 side. If the spring rate of the wheels (not the same as spring rate) is 250 lbs/in, you would have 500 lbs/in for the 2 wheels reacting 1000 pounds which makes the side roll 2 inches. If you doubled the spring rate, you would have 1 inch of body roll. The sway bars add stiffness in roll, and help initial turn in, but at the limit of tire adhesion, they hurt you because they are trying to lift the inside tires off of the ground and 4 tires grip better than 2. The shocks (really more properly called dampers) do nothing in a steady state situation, but add to these forces in transients like turn in, corner exit, bumps etc. If you wanted to maximize some skid pad numbers on a billiard table smooth constant circle, you would not want the sway bars at all, and would not need shocks either. However, the real world has bumps and you are not always in a perfect circle. The wheel rate that you want for bumps and to control dive under braking, and squat under acceleration, is not the same as what you want for cornering (if for no other reason, than the car is about 2x longer on wheelbase than it is wide, so the moment arms are different). This is why you need a sway bar, to add sideways stiffness, and shocks to dampen the transients for smooth transitions in and out of corners, etc. Cars with soft springs and big bars feel good, but have lower overall cornering capability because they are trying to lift the inside tires. Examples of this are Miatas, which feel great on the street but do not really generate big cornering numbers. We try very hard to run the smallest bars possible while having correct spring rates to react the forces while allowing compliance on the bumps both for keeping the tires on the road (note my repetition of this theme, tires need to be on the ground to work!). In addition, since bumps are by the definition transients, the dampers add forces to react bumps. Some shocks have very little bump damping, and basically linear rebound damping so that they can be both harsh on the street and not good on the street. With a sophisticated damper like the Penskes we use and sell, the damping forces are velocity sensitive and you get great control and good compliance (ride). In general, go with springs and quality dampers and leave the bars until last. This is most certainly not my idea, Gordon Murray of McLaren, Carrol Smith, et all preach this.
You mentioned the C6Z versus your car. In my personal C6Z, the stock rates were way too soft to prevent bottoming at NHMS frequently. With the dual rate springs on the Penske setup we use and sell, we use stock sway bars. The spring rates are not harsh on the street and are capable of reacting the forces that are generated on sticky tires at the track.

LOS ANGELES PI

Gary, you need to cut back on the coffee.

burners

Gary's just back from vacation and ready to take on the world, I see.

Gary, nice write up but didn't I say that (only without any explanation)? hehe

LS3FORME

While on the topic, the vette uses the transverse leaf composite sping, and some of the coil over manufactures , rec. not using the leaf spings and some use them. I have had coilovers on my last two race/track cars and it is a world of difference in rebound , control and cornering, but do we need the leafs? IF the coilover have adequate spring rates?

ghoffman

Yea, I had a few cups of black coffee this morning. I think that is the most I have ever written in one post! Well, I did not want to just say "sway bars suck" or something like that without some explanation. I do say that you should use the leaf or the coilover but not both. I think that using both is really dumb. For one thing (among many) how do you set the corner weights with redundant height adjusters on each corner? I do admit to eating a little crow on the whole coil over issue, since for years I maintained that spring rate was spring rate. I definitely now say that the coilover works better than the leaf, for a given spring rate and shock package.

LOS ANGELES PI

This is all good stuff.

Back to the original poster, I dont know how much track experience you have, but if it is minimal, you may be causing excessive body roll by the wrong line. In essence, you may be overdriving the suspension for the line you are taking.

If you run out and throw on a different suspension setup, you will only be faster through the wrong line, however, still slower than you would be with the stock setup with the right line.

Wring out what you have. Only then will you fully appreciate and understand the changes you make to tires, suspension, brakes, engine, etc.

trumper Z06

Gary,
can you please clarify the difference in handling... between the tranverse leaf spring vs. full coil overs. I too understood a "spring" was a "spring"...

maybe old college physics.

Thanks.

ghoffman

I am not sure that handling is any different in terms of grip on a smooth track, but for sure the compliance over bumps is much better with the coilovers. When we developing the dual rate coil over setup on the Penske 8100's, it was getting late one night and I just wanted go home. I had the leaf on the rear and just grabbed a pair of 850 lb/in Hyperco coil springs since I really did not want to put the front leaf back on. I assumed that my kidneys would be pounded on the way home, but the front end worked better that the rear. Now, I have to say, the rates we use is alot higher than the OE leafs, but the compliance is better than the leafs. My theory is that the friction of the leaf adjuster is part of the cause, and if the leaf had a roller like a rocker arm perhaps it would improve, but as I said, the coil over does work better, no question.