mark kibort

As there are lateral Gs applied, some how the geometry raises the chassis based on those forces. (the tires would do this as well, due to lateral gs on a tire, deforming it. if it deforms, it will become taller)

and /or, any lateral Gs lifts the inside of the car up, thus creating more air to go underneath the car and reducing downforce. less downforce in the turns, the car rises. This is probably the main reason for the increased ride hight in the turns.

mk

Dennis K

Don't Indycars run 3rd springs & shocks to separate pitch from roll?

Could you interconnect the two systems to deliver more ride height during roll? Run a link from the bellcrank to the third spring/shock assembly.

I remember Lola used to (still do?) have a shuttlebar system on the front of their cars that was supposed to do something like this.

NJ-GT

I think that during corners, with such high spring rates, the loaded side (turn's outside) doesn't change that much on height, but the unloaded side (towards the Apex) will tend toward lifting the inside wheels, so the actual height at the car center gets higher at the turns on both axles.

mark kibort

And thats why you would have less down force, especially in high speed corners, thus creating a higher ride hight. in fact, even if the spring rates on the outside were not moving down much initially (ie compression), the downforce overall being less would raise the car overall.

mk

Bull

My less downforce arguement was rejected above.

leif997

perhaps the lateral wind shear vectoral forces cancel out a portion of the downward forces in turns....angular momentum wants to keep the tires going centrally but the lateral g's meeting opposite wind vectors must contribute somewhat to this allowing a bit of spring decompression....an example of attempt to combat these forces can be seen on the dirt track race cars with those huge vertical wings...can't imagine how much more significant these forces are in an Indycar, its got to be immense at those speeds...chassis are probably just about to achieve lift-off!

Veloce Raptor

I am still going with my burrito argument. He didn't reject it!

SundayDriver

Some very funny answers and some pretty good ones too. While the tires may grow they are not going to move that much. It is also not downforce related. While we usually think of "lower = more downforce" that is not true if you go too low. The ride height they want down the straight is too low for good downforce - rather it is for minimum drag.

Mark K got on the right track about suspension. It is all about roll center and this was a great example that finally let me better understand what roll center is really all about. We are used to cars that have the roll center pretty much centered under the car - normally on the centerline when the car is level and not moving much with roll. We also expect cars to have the roll center below the center of gravity (CG). These cars take a corner and lean to the outside usually resulting in the inside ride height going up while the outside compresses.

Now if you have a high roll center, then it is like a hanging roller coaster and the car leans into a corner. In this case the roll center is WAY outside the car, so when the car rolls, both sides go upwards. There may or may not be 3rd spring coupling - that was not discussed and we were not given specific details of car/driver/year/etc as that was confidential.

Claude went on with some NASCAR examples which further raised my opinion of the technical skills of those teams. We all know that they run different alignment, tire stagger, etc. What I didn't know is that they design the suspension to provide a desired tilt to the roll axis (the first example had a pretty level roll axis meaning the front and real roll centers were about the same when viewed from the end of the car). Bascially they can create a suspension design that somewhat acts like active suspension because it bahaves differently under different forces - e.g - make the front drop down in a corner while the rear rises and drop the car down the straights for lower drag or force the tires to do certain things in corners vs. straights that are not the obvious reaction.

I came away with a lot of new knowledge and an understanding of how freaking little I know about race cars.

Larry Herman

Roll center technology = true race car engineering = not in my portfolio!

Veloce Raptor

Claude.....now there's a name you don't see every day.

SundayDriver

True for most of us but it can certainly affect what we do. I saw a photo of an early 993 GT2 that had been lowered (a lot). Anyone who has ever been around race cars could see that they were in for trouble with the severe angles on the suspension arms. Some knowledge of this stuff can help us much better understand what can and does happen when we simply lower a street car.

I came a away from this seminar feeling like I had certainly gotten my money's worth.

SundayDriver

Doesn't everyone work with at least one "Claude" and one "Bubba"? Where is the diversity in your life?

Larry Herman

Very true. My car is very low, and Chris C. set the rake angle at 0 to offset the lowered front roll center. Raising the back makes it much worse, but people are always talking about how much rake a 911 should have (1", 1.5", 2" etc). In some cases it should be flat.

Sounds like many of us with some knowledge could have benefited from it.

993944S2

What seminar were you at?

Veloce Raptor

Heh...I am an equal opportunity offender...I hate everyone!