Maineiac

I just weighed my car on a new set of Longacre scales. Help me decipher the results, and recommend which adjustments should be made.

The car: 2003 Z06, stock swaybars.

Weighed with just over a half tank of fuel, with driver.

LF RF

936 835

LR RR

810 778

Left side TOTAL = 1746 52%

Right side TOTAL = 1614 48%

Front TOTAL = 1772 52.7%

Rear TOTAL = 1588 47.3%

TOTAL WEIGHT = 3360

CROSS WEIGHT = 1646 = 49%


Thoughts? Looks like it needs more Rear weight....what about the CROSS %? Is 49% good?

davidfarmer

you should look at relative front-to-rear distribution on each side. Your left side is 1.15 front/rear, and your right side is 1.07. This will cause the car to have more rear grip in right handers, and more front grip in left handers.

You are at 49% rf/lr, so I would try and get 49% lf/rr and check the distributions. You want the get the cross weight AND the front/rear distributions as close as possible. This is how you ensure the car turns both ways predictably.

TedDBere

And make sure your scales are level or at least in the same plane. And disconnect your sway bars. FWIW

wtknght1

Those numbers aren't too bad, but with your stock bars, there's just so much you're going to be able to do with them. I don't know if you had them disconnected or not, but you need to when doing your initial scaling.

Once you get the cross weights fairly close, then try to zero your sway bars (not loaded/binding). To do this though, you really need adjustable sway bars or a lot of luck that your car is just naturally balanced.

In contrast to yours, here were my last corner weights...me in the car, just shy of 2 ticks of fuel:

LF: 878
RF: 828
LR: 807
RR: 763

Total: 3276
Cross weights: 1635 and 1641

Maineiac

I didn't have the sway bars disconnected...I just rolled it on the scales to see what the weights were.

wtknght1

That's kind of what I figured. I hate to tell you this, but unless those sway bars were zero'd (highly unlikely), those corner numbers aren't valid.

Setting up a suspension is really an art, which is why I preach about the Phoenix guys so much - they know their stuff and do it right!

davidfarmer

yeah, but Phoenix charges big money. Scaling a Vette is easy, and takes no time at all. Learning to do it yourself, and doing it right, will be an excellent experience. Assuming you BOUGHT those scales, get ready to be the most popular guy in your neighborhood (of racers, that is)

Maineiac

Since the stock sway bar ISN'T adjustable...how different could the readings be with it unhooked? And why are the unhooked readings so important?..don't they change when you hook the bar back up?

You don't run with the bars unhooked, so aren't the numbers more important with the sways hooked up?

It's all new to me...I'm thinking out loud here, so bear with me...

Solofast

While it is absolutely best to do it with the sway bars uncoupled and then installed without preload the results will still be vaild if you have preload in the bars, it just may not stay that way for as long as you might like. If the bushings wear, or the bar shifts, you pretty much have garbage because the preload on the bar changes....

I've been doing corner weighting with stock class cars for more than 25 years and found that it depends on the car as to weather or not the settings with preloaded bars will drift off with time.

Most of the cars (that had some bar preload present) that held the settings the best had sway bars that were mounted in rubber grommets that twisted with the bar and didn't slip. That way there wasn't any relative motion or wear, and the swaybar preload stayed there just fine. In fact, on one car that didn't have height adjustments for spring preload we did ALL the corner weighting with the adjustable front bar links and it repeated cornerweights within a couple of pounds a year of daily driving and 30 weekend autocross events later. That was a reliatively small light car, but it worked well enough...

The cars that had "corner weight drift" over time were the ones that we had poly bushings, bar preload, and we could see some wear in the bushings, or could see that the bars had shifted to one side or the other. On one car we fixed the shifting of the front bar by clamping a split piece of aluminum on each side outside of the sway bar bushings, so that the bar couldn't move from side to side..

Not sure if our cars, with the greased poly bushings would drift or not, but I agree that preload isn't a good thing in so much as the bar on our cars will tend to work from one side to the other if there is any significant preload and that isn't good.

But sometimes you gotta do what you gotta do.

outnumbered

Phoenix just did mine. Those guys are great. I also think they are very fair. $$

The difference in the handling is huge.

wtknght1

HUGE!! As has been stated, the sway bars help transfer weight from side to side and if they are binding/loaded then your corner weights are somewhat misleading.

What you'd like to see are the same numbers...whether unhooked or hooked - that way you know the bars are unloaded. When the bars are zero'd properly, then as the car sits on level ground, there's no stress on the sway bars. Once you go into a corner though, the sway bars take over, load up and limit the body roll.

If the bars are preloaded, then at some point in your turn (either left or right), they will unload (neutral) and the handling of the car can/will change.

What you're looking for is consistency and predictability.

The Phonenix guys start off by setting the correct ride height, which I found was crucial for a well-handling car. They get the control arms in the right spot and also the rake. Once they do that, then they start making small adjustments to the spring bolts to even out the corner weights. All of this is done with the bars unhooked. Once everything is even, they hook the bars back up...with no load. It makes for a much more pleasant car to drive (not to mention faster) - both on the street and especially on the track.

To complicate matters, the spring bolts on the Corvettes turn on their own while you drive the car!! The front bolts sit in the lower A-arm cradle/wedge and the cornering forces actually turn the bolts, which of course is going to change your rake, corner weighting and sway bar neutrality. And Oh did I mention that the springs do get "tired" as they age which changes all the stuff too. It's very difficult to get these cars in a "perfect" spot and even harder to keep them there for ANY length of time. They not only change from year to year, but from track event to track event...and even lap to lap!

davidfarmer

Chris is playing devils' advocate to some degree. The leaf springs have memory, so the weights can change some on their own. Don't be surprised is you weigh the car, make a physical change, roll back on the scales and the numbers stay exactly the same. It just happens. You develop a feel of what is happening, and you can find the right setup based on a combination of instinct AND measurment.

The springs bolts CAN turn, but usually don't. I always mark mine with paint (just like I mark the concentrics), and it is very obvious if something has moved. They usually don't. HOWEVER, the springs can change over time, and ride height and corner weights can suffer.

I recently re-scaled and re-rideheighted (sorry) a car fresh from Phoenix. The springs were brand new, and they appearantly settled. The left nose of the car was on the ground, and the right rear was jacked WAY up. It was obivous both visually, and with measurments, that the car was not supposed to be this way. You don't usually see this on seasoned components, but just keep in mind that things CAN move/settle/break/stretch over time.

ghoffman

With Chris and David but the real issue in this case is that gravity is different in Maine. I went there last month and I came back heavier for some reason.

AU N EGL

All those Lobsta dinners Gary.


Dont forget to weight your car with you or your weight in the drivers seat.