Chassis flex

[GT1]

Its usually not a good sign when a car, like the Reynard 2k, has a chassis flex. I hear a lot about it but can anyone tell me what a team or manufactur can do to fix it?

If the aero package is bad, you go to the wind tunnel. If the driver is slow, find another, etc. What do you do for chassis flexing?

[billnchristy]

patch it? start over?

[MulsanneMike]

Increase the laminates and/or alter the fiber direction in subsequent tubs. Cuncurrently strengthen the bell housing and rear subframe...You'd also be surprised at how by simply bolting the sidepods permanently to the chassis increases overall stiffness. In torsional testing of the R&S Cadillac that was one of the edicts, that the sidepods were to be permanently rivited to the tub. In that frame, the floor is an easily reproduced composite part (compared to say a tub) and increasing that part's strength will also help in overall reductions in chassis flex. There are many ways, but the key is finding the source of the flex and then addressing it.

[marcush.]

I´d say a Sportscar is quite different to a formulacar in the fact that you have big jumps in crosssectional area (of the Chassis).Because of the wide Monocoque (wich is potentially very stiff)you get massive Problems in the area of Engine Mounts and of course Bellhausing and Gearbox.
Consequently almost all sportscars use some sort of Tubing triangulation running from the rear bulkhead of the monocoque to the bellhousing /rear of the engine,putting the engine only in semistressed load.

[KWM]

The Torsional stiffness of a car is very important for the vehicle dynamics, although there is a point beyond which the returns in vehicle dynamics deminish.... however a very 'soft' chassis will not respond well to suspension changes. The 2KQ initially exhibited these problems.

The problem with sportscars is actually the monocoque itself (or at least it used to be in Reynard 2KQ days) where the tub is very wide to accomodate the regulations and has a very large hole in the top of it (cockpit opening) this is not a perfect structure. Modern cars are allowed far more structure in the cockpit with the central beam now helping make the tubs stiffer and of course safer. Generally the bellhousign and gearbox is easy to make stiff, it has sensible load paths, and if you have a proper race engine like a Judd V10 then the engine can also be used as a structural and carry load to the tub, the engine is known then as stressed. Generally however the tubs are much wider than the engine interface and so there is not a good load path into the tub, so the a-frames are almost always used to take the loads from the bellhousing directly to the most structural part of the tub, its corners. A-frames are even more important if you have a non-structural engine or a very small engine like a 4cyl.

Because of the diversity of engines fitted in sportscars it is often the engine installation that is the weak point for the overall chassis stifness as it was on some of the engine installations on the 2KQ, for example the Ford V8's and the Chrysler Mopar engines could not carry any loads and had to be protected from any stress by the a-frames... this comrpomised the overall chassis stifness. Also the tub in the cockpit opening was found to be a weak point and this was easily fixed with two longitudinal beams down each side of the cockpit giving the tub walls around the cockpit opening more section and stiffness. New a-frames and the tub stiffning brought all 2KQ installations up to an adequate level of stiffness, in fact in excess of a Champcar single-seater.