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View Full Version : Hey Pozzi's, I still don't get it?!



Damn True
11-12-2008, 03:30 PM
I didn't want to further hijack the Optima thread so I'll put the question here.

Steve's car understeers a bit right?

Am correct in my recollection that the "stiffer" (tire-p, spring rate, roll resistance, compression damping) end of the car will lose traction first?

If that is true, wouldn't adding additional roll resistance make the front of the car even "stiffer" and thus more prone to a loss of traction?

hotroddr
11-12-2008, 04:27 PM
Adding roll stiffness to one end of a car will tend to make that end lose traction more relative to the previous configuration.

So if you started with a neutral handling car and increased the front roll resistance, the front would tend to break free sooner than the rear resulting in understeer. Did that answer the question?

Chad-1stGen
11-12-2008, 07:12 PM
That is what he was infering I believe. However, that appears to be in opposition to the advice Steve has received...

David Pozzi
11-13-2008, 08:41 PM
I didn't want to further hijack the Optima thread so I'll put the question here.

Steve's car understeers a bit right?

Am correct in my recollection that the "stiffer" (tire-p, spring rate, roll resistance, compression damping) end of the car will lose traction first?

If that is true, wouldn't adding additional roll resistance make the front of the car even "stiffer" and thus more prone to a loss of traction?

For an understeering car, you need to stiffen the rear, then the rear will carry a larger percentage of total roll, this reduces the load on the front tires.

Before the event, I did tell Steve to get a larger front bar, based on how much he stiffened the rear, plus raised the watts link pivot height. But he ran into clearance problems and didn't get it on the car. Lucky for us, because the car understeered as it was. I didn't spec a very stiff bar, only 50 lbs stiffer, I was afraid to go more. The software was showing "neutral" handling but it's not there yet. The software assumes equal sized front and rear tires, there isn't an input for tire size.

The car was pretty close to balanced on LH turns, but on RH turns it was pushing quite a bit. This is frustrating to deal with for the driver. We only got 1 g cornering on RH turns, 1.2 or slightly over that on LH turns, due to the uneven corner weights. We scaled the car but I wasn't sure the floor was flat, and there was a line of cars waiting for our spot in Tyler's shop. I did try to make an adjustment but could not break the adjusters loose with the coilover on the car.

If the car was already very stiff in roll, I'd reduce bar or spring on the front, allowing more roll angle, but Penny has lots of roll right now, but getting close to where I'd like to see it. The car is very compliant and "tossable" very hard to upset it. I found it very easy to drive, just hopped in an drove the snot out of it like an old friend. It was like the good old days autocrossing my 67 Camaro. I put 150,000. miles on that car.
David

Damn True
11-13-2008, 11:40 PM
Ahhh, now I understand. I thought you were still looking to put that bigger bar up front.
So how much do you reckon there is to be gained by optimizing tire pressures and temps? Or perhaps a more aggresive alignment? I mean the settings Steve mentioned (was it .8deg - camber?) seemed a bit on the conservative side.

Was it pushing at turn in, mid corner or throttle on?

To be clear, I'm not questioning you, just trying to wrap my head around it. Thanks.

Steve1968LS2
11-14-2008, 07:51 AM
Ahhh, now I understand. I thought you were still looking to put that bigger bar up front.
So how much do you reckon there is to be gained by optimizing tire pressures and temps? Or perhaps a more aggresive alignment? I mean the settings Steve mentioned (was it .8deg - camber?) seemed a bit on the conservative side.

Was it pushing at turn in, mid corner or throttle on?

To be clear, I'm not questioning you, just trying to wrap my head around it. Thanks.

Well, we still might put a larger bar up front.. once we put a bar in the rear. The old "more bar, less spring" deal.

The alignment was my "street" alignment.. which is a hair more aggressive than a stock C5 Z06 alignment. Didn't have time to rack it.

I think the car has a LOT more in it. Next year we need to have it set up before we arrive. Tyler's lift is way too popular. lol

Steve1968LS2
11-14-2008, 07:53 AM
Oh, and it made me smile when Dave told me that the faster he went the better it was (to a point or course).

The car does what you tell it to and it's very hard to upset it and get it squirly. When it does it's very easy to recover.

David Pozzi
11-14-2008, 08:51 AM
I'd say Penny has more of a Guldstrand setup, stiff springs and soft bar. If the watts pivot could be moved to the top hole, it might be pretty close. The higher the rear pivot, the more jacking effect there is on hard cornering, this problem would show up as the rear lifting and settling. We need something that is adjustable to balance oversteer/understeer.

I'd like to see the larger front bar on it and then add a rear bar stiff enough to balance it out, leave the watts where it is.
David

Damn True
11-14-2008, 10:43 AM
It's currently in the center position right?

Here's a silly question.

Steve,
When you had the car aligned did they check all four wheels? I mean if the rear was offset L/R a bit would that potentially impact how the car behaves turning left vs right?

David Pozzi
11-14-2008, 08:17 PM
Somewhere he's got a pic of the scale display. It isn't pretty.
I don't think the axle centering has much effect. Now go-karts use spacers behind each wheel to affect handling. Widen the track, and you get more stick on that end. Pretty basic way to adjust handling.
David

ITLBTU
11-17-2008, 12:40 PM
What would happen if you changed the "cross" weight? Does the car have coil overs all the way around? If the cross weight is neutral with out the driver, or crossed the wrong way it would turn better one way as opposed to the other... wouldn't it?

David Pozzi
11-20-2008, 01:35 PM
It had a lot of cross weight. Left front and Right rear had more weight. The car had more understeer on RH turns, but still some understeer on LH turns but plenty manageable in that direction.
David

406 Q-ship
11-21-2008, 09:26 AM
With the understeer being different left to right turns I would be look at at gets the corner weights better. After that I would then play with bars and springs. I used to work for Guldstrand back in the late 80's, yeap he liked a stiff spring then used the swaybar to bring the cars handling in, but on a car like Penny we would only use 600 to 700 pounder in the front (depending on leverage points, this is what we used on OEM suspension 1st gens). The ride was stiff and shock must be up to the task of controlling the stiff spring, but it made the limited swaybars available for the 1st gens work.

Could the unbalanced be a swaybar with uneven loading?

Damn True
11-21-2008, 10:36 AM
IMO it seems like step one ought to be getting the car corner weighted and aligned with 200lbs or so sitting in the drivers seat then take the thing to the track again before making any other changes.

David Pozzi
11-21-2008, 01:14 PM
True,
A good idea, but I'd also like to have something else "in hand" to try on the next test, like a rear bar. Right now, there is really nothing that can be adjusted at the track except rear pivot height, and it's at the top.
David

Damn True
11-21-2008, 02:11 PM
Oh absolutely have the ability to make changes once some testing has been done. But I can't help but recall taking over a helicopter main rotor track and balance that someone had made multiple changes on and wound up chasing my tail. One change at a time right?

Like I need to tell you this? Duh....nevermind.

406 Q-ship
11-21-2008, 04:33 PM
Just keep adding more and more air pressure to the left front and right rear to balance the car out.......:idea: :lmao:

David Pozzi
11-21-2008, 09:57 PM
One at a time is best, but if I were way off I'd cheat a bit and do a couple of changes at a time 'till I got close. Like if I knew the front springs were soft and we had understeer. I'd stiffen the front and you just know the understeer is going to be worse, so you need less front bar or more rear bar.

If your test is at an autocross you have mere minutes to make a change before your next run.

Steve1968LS2
11-21-2008, 10:09 PM
It's currently in the center position right?

Here's a silly question.

Steve,
When you had the car aligned did they check all four wheels? I mean if the rear was offset L/R a bit would that potentially impact how the car behaves turning left vs right?

The car is square to within a tenth of an inch.. The problem is in the design and I wasn't building a racecar.

The left front corner has the PS pump, the alternator, the remote oil filter, the sterring column, the brake master and a bunch of other stuff.. the other side has almost nothing.

Will be tackling this and working to get the car squared up. Might move my battery from the right rear to the left rear...

Steve1968LS2
11-21-2008, 10:11 PM
True,
A good idea, but I'd also like to have something else "in hand" to try on the next test, like a rear bar. Right now, there is really nothing that can be adjusted at the track except rear pivot height, and it's at the top.
David

There's one position higher on the Watts but I need to remount my regulator since there's a clearance issue. (it's on the third position up.. 10.25" roll center)

David Pozzi
11-21-2008, 10:34 PM
I'm thinking the highest hole is pretty darn high, the car might want to hop coming out of high G turns due to weight jacking if we go higher.

I think the corner weights will get a lot better with some spring perch adjustments. The left front will always be a bit heavier, but with perches adjusted better, the rears should be very close to even.