fatbillybob

I would like to hear the comments of others on corner weight compromises and different corner weight set-ups for a C5. WE all know that 50% cross is ideal but is there a good reason to not have 50% cross in the C5? People say the C5 drains one gas tank first and then the other. If so then the typical scaling job involves 1/2 tank of gas meaning all the fuel is on one side. What is the best compromise fuel gage tank level for scaling a C5?

Solofast

There are plenty of reasons to jack some cross weight and it doesn't necessarily have to do with just the fuel load change.

For instance with C4's in SCCA solo II we were restricted in couldn't get as much negative camber on one side as the other. In that case it helped to jack some weight off the left front since that corner was "camber challenged" and the car would push on right turns if it was properly corner balanced and the car was faster if you skewed the balance.

The C5 is a much better car and you can can get an equal setup in terms of alignment. Relative to the fuel weight offset, it depends a lot on how much fuel you expect to have when it is most important to you. Your balance is going to change some as you burn off fuel, so if you want to be stronger, say late in the race, you might set the car up to balance it with almost no fuel.

You might see your front tires going off late in a race and might want the car set up to not work the LF tire as much, so as not to beat it up, with a bit more bias on the LR. Since the RF doesn't get nearly as hot, you might not care if the car is set up with some extra weight on the RF, so as too avoid late race push that would develop from abusing the LF tire.

Since, as the fuel load burns off, more of that weight is coming off of the LR, the balance is going to shift more toward push in right hand corners as fuel is burned., just when the tires are getting tired, the balance is going more toward push. It's going to depend a lot on what size tire you are running and whether or not you are running out of tire at the end of your run.

Either of these situations might make you want to bias the balance to run a bit more rear weight on the left side and that might makes sense. There are probably other reasons to change the bias the other way, but I can't think of any off hand.

travisnd

Timely thread... I'm taking my car to my buddy's shop in weekend after next to weight/align my car. It has 3/8ths of a tank in it right now and I was going to leave it that way so I could make sure I was over min comp weight etc.

fatbillybob

Solofast,

You are thinking like I'm thinking. I have found it easy to scale the C5 to perfect 50% cross but I'm not convinced that is the best place but where everyone will tell you to statically balance the car. If you don't follow dogma people think you are just wrong. I think the concept of "balance" is wrong. I think the "scaling" should be done to optimize dynamic weight transfer in the same way someone might set up a car ideal for the most important turn on a track. If any of you buy that argument then how do you take the empirical concept of managing weight transfer to some real numbers finally ending up as turns on our rideheight adjusters?

RacePro Engineering

Bob,

Great topic!

As I have mentioned several times, we are big believers in letting the car "tell us what it needs". As you probably know, there are generally two schools of thought for proper corner balancing an asymetrical car - one strives to achieve 50% wedge, and the other shoots for precisely equal weights on the front corners. There are certain (small) benefits to be had from each system, and I believe the pro teams are split evenly about which they prefer - there is no clear "winner".

For us to start jacking corner weight in a manner contrary to these two well-accepted methods, we would need a very compelling reason to do so. The car would have to be telling us it needs something "special". Further, it would have to be behavior that could not be remedied through typical adjustments to tire pressures, alignment, anti-roll bars, or damper settings. Something like, "In EVERY left-hand corner, the car understeers, but never in right-handers."

Thinking of the concept of jacking weights in an unorthadox manner, there almost certainly would be undesirable side effects. [1] Your carefully executed suspension alignment will be compromised. [2] Corners in which the car used to be happy have now become difficult. [3] Braking in a straight line now becomes "dramatic".

In short, doing "custom corner weights" would have to be demanded by the car for some reason, and ON THE TRACK. That is how we would approach it.

Ed

AU N EGL

My Car needs a better driver.

CHJ In Virginia

Newby here on the topic of corner weighting. When you are making the adjustments should you consider the drivers weight ? I'm just shy of 200 LBS, so that much weight will make a definite difference in the balance. Should 200 LBS be placed in the drivers seat to simulate actual driving conditions when performing the suspension adjustments ?

Solofast

Yes

(another one of my long winded posts....)

RacePro Engineering

We are right there with you, Tom! And, speaking for us, so far all the "adjusting" we have done has been to no avail.

Ed

AU N EGL

Ed Yup

fatbillybob

No I did not know that. I'm a good monkey but often times don't know why I'm doing something others have told me to do. So I'm trying to get my knowledge up to my pretty good ability to use tools and my opposable thumbs.

method 1:
So with that clarifying statement I only know of the 50% cross method who's claim is to control a chassis tendency to oversteer or understeer through weight jacking. In our road use that means going for 50% cross or neutral balance. Words get funky so in math terms: RF+LR/TOTAL WEIGHT = 50% cross weight

method 2:
Then I read about another corner weight theory specifying equal percentages of front to rear weight relative to front and rear axles. This claims to make equal left and right turns and equal rideheights per axle:
LF/LF+RF=LR/LR+RR
Any comments about this method?

method 3: Equal front wheel weights. What is the theory behind how this works or can you point me to a link on the subject?


Solofast's ideas are more about what I am thinking about which is how to dynamically take advantage of corner weights. Should we be thinking more about this or more about the static corner weights as a referrence point and use other tools shocks etc to tune for fuel weight changes and overwork of a tire or late race push?

froggy47

If you do ride height first, then corner weights (either formula) using adjuster bolts, then go back to check ride heights, they have changed, right?

So are ride height settings always secondary in importance, to corner weights?

fatbillybob

Lets see what others have to say about this but my thinking is that ride height is a basic needed for basic operation of the chassis. The corner wrights only change the RH (rideheight) in small ways because we hope to have a straight frame reasonably well balanced by design. I guess my real reason for spewing all this stuff is to try and gain a deeper understanding of the compromises with all of you guys as sounding boards. So thanks for all the replys. Back to RH my minimalist thinking is RH should be 0" to lower the CG but obviously that does not work. We know in the C5 there are 2 important aspects that RH effect and that is shock travel and aero where RH is really chassis rake. No one talks about C5 bumpsteer so it is either not an issue or no one has measured it. I have not. We also know that stock bolts and slamming a C5 while lowering CG will make you slower. To start gaining a roadcourse advantage in that game you have to go to drop spindles and properly sized shock bodys.

Crepitus

re ride height; keep in mind that to, for instance, increase the left rear/right front cross weight you have the option of jacking more weight on to the left rear and or right front or jacking weight out of the left front and or the right rear. Allowing ride height adjustments at each corner. In addition equal adjustment to each side of either axel (rake) will not effect cross weights.
and another great thread!

Painrace

That is always true! We can all learn and go faster!

I am amazed that stock Corvettes are faster today than race Corvettes were 10 years ago! GT-2 Corvettes are running 1:18s at Road Atlanta! But, not with me driving!

Jim

Solofast

What I'd be doing is to set the front suspension of a C5 to where you want it and then don't mess with the front ride height screws. The reason for this is that the pads on the screws deform and take a set. If you start jacking with these screws once they are deformed you don't know where you are going to be when it settles out and the plastic heads deform. Besides once you get used to it you will be able to jack weight with the rear screws fast and easiliy. After you do it a bit you will get a feel for how many turns it takes to do what you want to do and you will be able to dial it in pretty quickly. I do that with front swaybar preload and it's amazing how you can dial it in at an autocross, between runs, and get it real close to right with one, or at most two tweaks with the wrenches.

There's nothing sacred about having the front wheel weights equal unless you are turning left and righ the same amount, and I haven't driven any road courses that had that feature. I'd just be looking at what the car does over the length of the race, and on what course it happened on. Keep track of how much adjustment you are using ( rear screw turns (and generally just turn one side only), and learn what it takes to keep the car fast over the race.

Tires are going to effect it too, bigger tires on the front won't go off as bad as skinnier tires, so you are probably thinking about less adjustment if you are running closer to a square setup which makes you go to a more classic equal cross weight setup.

yooper

Thanks for sharing

RacePro Engineering

Bob,

We have had many rewarding discussions with SoloFast, and have a great respect of the thought, backed up by experience, that goes into his posts. And, as we continually see here on the Racing and Autocross Forum, the two styles of autosport often require drastically different setup parameters. Essentially, what works incredibly well at 60 MPH, may not work at all at 140. Many of the basics are the same for each, and many are different. Naturally, our perspective is road racing.

By its very nature, measuring and adjusting corner weights is a STATIC process. It requires a car sitting perfectly still, on a perfectly level surface, with as much suspension pre-load as possible removed, except for the weight compressing the springs. While we take great pains to get these STATIC weights “perfect”, once the car rolls off the scales and onto the track, everything changes!

So, why even do this exercise?

If we were racing on ovals, it is fairly easy to predict what sort of UNequalization we should dial into the chassis: always turning left (or right); very LONG, sweeping turns; hard braking is minimal.

But we are road racing; turning both left and right, often with brutally fast transitions (chicanes); accelerating most of the time in a straight line; and braking at maximum Gs from very high speeds (even if we are trail-braking into a turn, we want the car's natural tendancy to be straight-line).

Doing corner weights on an asymetrical racecar, by definition, means that one will finish with either: [1] Very close to 50% wedge (your Method 1), OR [2] Close to equal weights on the 2 front corners (your Method 3). The differences are subtle, but 50% wedge typically offers more consistent mid-corner transitions; while approximately equal front weights typically helps more with high-speed braking stability, and with rapid left-right-left transitions.

As I mentioned, one driver may prefer Method 1, while another equally expert driver may prefer Method 3. Indeed, a third driver may want one setup on Track A, and another on Track B.

Ed

VetteDrmr

So, how do you distribute the ballast representing the driver's weight? I would expect maybe 2/3rd in the "rear" of the bottom cushion, 1/3rd on the front of the cushion.

Does it make any real difference?

Thanks for the help, and have a good one,
Mike

Solofast

I agree with Ed, you need to look at the track, the driver, the car, and what works for you. He is right in that in an autocross car you are going to look more for equal balance and tend to do an equal cross weight because you don't know from one day to the next if your course is going to be all lefts, all rights, for anything in between, and he is also right in that you could accept and live with more oversteer and a funny setup on an autocross course because you aren't going that fast, and a spin ruins a run, where on the track it could ruin you life.

You need to look at what track you are running, where the high speed corners are, what corners are entering the straights, where you want or can live with a bit more oversteer to save your left front tire if you are overcooking it late in a race. It isn't at obvious that you want a perfect square setup, but that's a time proven good place to start. And don't expect the same setup to be right for each track, or for different days on the same track. You need a few realiable adjustments to be able to twist and get the final setup dialed in.

These cars do have more weight on the drivers side, so that alone makes the setup a different issue than a car that is balanced. It would be nicer if we ran road courses in the other direction, with more lefts than rights, but that's just wishful thinking, and it isn't going to happen.

Pat Bedard once described setting up a car for the Indy 500 as a 200 mph rubix cube. There were so many things that you could adjust and tweak and in the end if it wasn't just right it was crap.

A good setup for a car on the track is still a rubix cube of tuning selections. You can tweak ride height, rake, camber, caster, track, tire sizes, 1,679,676 shock settings (assuming 6 jounce and 6 rebound settings per shock and four shocks), sway bar settings (if you have adjustable bars), or bar sizes and bushing sizes, never mind even bothering with different cross weight combinations. The fact that you can get a car to handle really well is actually a bit of a miracle. But somebody who knows how to solve the rubix cube (I never could) can twist their wrist a few times and all the surfaces are all the right color. The right setup for a track car is much the same. If you know what you want to do and have the experience in twisting the ***** you can get a good setup in a very short while (Hienricy is a perfect expmple of this, he KNOWS how to tune a suspension). If not you are going to be looking at a bunch of messed up colors, or funny (could be even dangerous) handling and a miserable weekend.

To do this successfully you have to learn what each tuning item does and how it effects your car, and remember they are all interconnected. You need to look at the way the car is behaving in lefts and rights and where in each corner it is working and not working. Then you have to either make a change with one of the tuning ***** or drive around the problem. Stock class solo drivers tend to use shocks and front bars because those were the only tools we had. Road racers have more tools in the toolbox, but you can also rubix yourself out with more tools since there are so many more things to tweak.