Z06_BluByU

Put the car on the scales while @ roebling road.. this is what I found..

Car and Full tank of Gas

LF:847 RF:893
LR:864 LR:761

Total: 3365



Car, Full tank of Gas and Driver (not to be named)

LF:909 RF:901
LR:956 RR:805

Total: 3571



Looks like I need to move something from the LR to the RR.. any ideas?

ZR1 MK

Moving the battery gave me near perfect cross weight and better front to rear dist.

astock165

Do you need to move from LF to RR or just add to the RR? The LF to RF looks pretty good.

If you do want to actually move weight from LF to RR the first thing that comes to mind is the battery. Put it in the cargo hatch behind the passenger seat. That does seem to be quite an effort though as I have looked into it (but I hate doing wiring ).

Solofast

What you are seeing is pretty typical of a C4...

You need to loosen the left rear height bolt until it hits the cotter key and crank in the right rear until you run out of nut travel. That will jack weight onto the left front and right rear.

Do it on some scales and try to get the cross weights the same. You may not be able to get there with the bolts that you have, but you should be able to get a lot closer than you are now.

rfn026

I love this. My C4 is going on the scales next week. God only knows what it weighs. I'm pretty sure the crossweights are totally off though. I'm going to try to get my track car down to 2700 lbs. This is going to interesting.

Richard Newton

101 Projects for Your Corvette 1984-1996

Autocross Performance Handbook

steve40th

My 93 Coupe with regular top, R/D racing rollbar, thick sway bars(ZO7 bars), 17x9.5 wheels A Molds front and 17x11 rears weighed in at a cool 3275 with half a tank, by the bars on the digital dash.
LF 895, RF 890,
LR 780, RR 710
W/Me in it
3480
LF 955, RF 880
LR 890, RR 755.

WNDOPDLR

My car came in almost perfect on corner weighting with the relocaton of the batterey and a pretty serious diet. Weights are with a full tank and me in the seat. They include the R&D roll bar and cross frame brace.

LF 825 RF801
LR 854 RR804
Total weight 3284

David Farmer worked his magic and corner weighting is now within 8#. Thedifference in "feel" while on the track is sooo much different since David worked on it. It feels very light on it's feet while not being twitchy, but it sticks better than ever.

Z06_BluByU

what did david do (or areas he played with)?

WNDOPDLR

David is a little tight lipped sometimes about just what he does and I guess I can understand his motive. He gives the folks here on the forum a lot of free information, but if he gave away all his secrets, he would be cutting into the income he uses for his track habit.

Having said that, I know he tweaked the tracking of the car, toe in, camber and castor and played with the corner weighting to get it nailed.

The results are really impressive. I took it to VIR and the car felt completely different from the feeling I have gotten used to over the last 3 years. It felt like a balerina but, at the same time, stuck better than it has ever before. Speeds of 150+ on the back straight felt as rock solid as it always had. I had some pretty worn out Goodyears on the back and oversteer was a bit of a problem by the end of the weekend, but I had also taken along a new set of Khumo's to heat cycle. I only had the one run on the new tires but it was definitely Unfortunately I did not turn on my DL1 for that session as I intended to run 6/10 max.

TT's at VIR in 2 weeks with THSCC and the DL1 will definitely be on.

astock165

With those static wts
doesn't he need to add balast to the LR before working on cross wt? I ask because I'm referring to the GRM article about Understanding Corner Weights and that's what I took away from it.

I'm also asking because I intend to put my car on scales in a few weeks so I want to make sure I do it right.

ScaryFast

Don't forget to unhook your sway bars when you're doing a corner balance. And of course put ballast into the driver's seat equal to the driver...

Solofast

With most C4's you are going to be heavier on the left side than the right when you put a driver in the seat. That's why C4's are usually better turning left than right, at least mine were, that is life, get over it..... Weights without the driver mean nothing, I don't even write them down anymore........

Put some ballast in the drivers seat and work from there...

It would be nice to unhook the bars if you can, but many C4's don't have adjustable links so you may or may not be able to unhook the bars when doing it, depends on the class you are running in and what is allowed. If you can it is nice to unhook the bars, but on the C4 the bars don't move around as much as on a C5. C4's have rubber bushings that are clamped tight on the bars, and the end links aren't rod ends. As a result, the bars don't tend to shift like on a C5 and there is less chance of things changing with time.

astock165

I totally agree that wts w/o the driver are meaningless.

Let's assume that 383 puts his car on the scales, with a driver in the left hand seat and gets the following wts:

LF:847 RF:893
LR:864 LR:761

He's obviously really light in the LR. My question is: would you add balast to the LR to get the static wt (again w/ driver added) to be more equal and THEN cross wt with jack screws? Or would you just go right to the jack screws to try to even out?

If I read the GRM article correctly (and I may not have), they were recommending getting the four corners right first (L to R equal, FR to BK per mfr spec) and then using jack screws to get the cross wt to 50%.

Z06_BluByU

BTW:

With Driver in the Driver seat..
LF:909 RF:901
LR:956 RR:805


I was advised to add ballast to the RR by a few of the guys at the track.. might try adjusting the spring bolts first..

ZR1 MK

Definitely disconnect the bars. You want a good base if you do adj links later or just shim them now if you dont have adjustables. My RR spring needed a 3/8" rise for near perfect cross weight, so I shimmed the left rear bar 3/8". I now have adg links in the rear. Front bars never need adjusting.

69427

I agree with your comment on trying other changes first. I'm puzzled by why anyone would recommend adding weight to a sports car. Weight is the enemy of acceleration, braking, and cornering. Given the weight/traction curve of most (if not all) tires, there's always a net loss of (cornering) traction when weight is added. Did they give any reasoning behind their suggestion?

Solofast

I fixed your quote, you had the LR listed twice....
In this case I would be looking at jacking about 33 pounds more into the RR and you would see an increase in the LF and a decrease in the RF. The corner weights would look like this:

LF:880 RF:860
LR:813 RR:794

That gets the cross weights within a pound, and you are done...You shouldn't be adding ballast. If you can move some stuff around, like the battery, then do it, but ballast is seldom a good idea...

astock165

OK, that makes sense. So you just work on the two cross-wt ratios and be done with it.

I'm assuming you just live with the ride ht you get when those cross-wts are 50% each (ideally)?

astock165

So was I. As I read the article again they said to move ballast first then adj with jack screws. I take this to mean (for example) move the battery to help the existing wt distribution, then use the jacking screws. Which seems to make a lot more sense.

69427

I definitely agree with your battery movement comment. Moving actual ballast in a minimum weight restricted race car makes sense, but I was confused about the use of the word ballast in previous posts regarding what I assumed was a street Corvette, and hence no pure ballast used.