Car manufacturers are even more using torsional stiffness of their new cars as a marketing lever, to cover up the 200+ kg avg weight increase on the previous model (to score 5 stars in crash tests and all that safety stuff...)
I was wondering why ts is so important for a car: I read that the more ts, the better the suspension response, because they move only the way they are designed to, not carrying over chassis flexxion in their cinematics.
It sounds quite important to me, but not that crucial: I think that to go fast is more important to weigh 200 kg less, than have +50% ts. Am I wrong?
200kgs sounds like a lot. Are you sure all those 200kgs are used to create a stiffer chassis?
To come back to your question, from my point of view TS only provides a better "feeling" because it makes your car more responsive. I cannot think of any safety advantage.
Torsional rigidity is important so that the front and rear suspensions act the right way relative to each other. If your chassis is a big wet noodle, all the suspension tuning and roll stiffness adjustment etc in the world won't do crap because your car is flexing so much. It has a huge impact on the cornering ability of your car, how much you can accelerate into, through, and out of a turn. Acceleration is the prime mover in racing.
The question is how stiff is stiff enough. One rule of thumb, that I'm not sure how great it is, is to have a torsional rigidity about an order of magnitude greater than the difference in roll stiffness between the front and rear suspension. Look at an F1 car going though a 4+ G turn, it doesn't roll much. Very high roll stiffness, thus high torsional rigidity required. I won't say which race series, but one manufacturer of CF monocoque cars has chassis so stiff that there are sections that exceed 10,000 ft-lbs/deg, with an overall value in the 5-6000 range.
Its not all that difficult to have an extremely rigid carbon fiber tub that's lightweight if its designed right and all the plies are laid out in the right orientation during layup. Not easy. Again, there's a racecar manufacturer in a different race series that when they laid up their CF monocoque, had a torsional rigidity an order of magnitude lower than they expected!!
That said, rigid chassis only helps the suspension. Not safety.
Grip is a four letter word. All opinions are my own and not those of current or previous employers.
i think the writers point was that because they have had to put on an other 200 kg to comply with the safety standards, they are making up for the addition by improving the driving dynamics via a stiffer chassis. and if it wasnt his point, to me it would at least seem logical
I was driving behind the new Nissan Tida this morning and couldnt get over how high the boot is, also the windows in the doors begin a lot higher up the car too. This is done to pass the crash tests, but makes the cars look like ---.
Torsional stiffness is a good measure of the structural capabilities of the monocoque assembly which is the main load bearing structure between the front wheels and the rear suspensions in modern passenger cars. Since all of the load comes through the tires (except during a crash or some other contact event), this load path is quite important. If you cut a hole in a box (similar to where the windows and such would be), you will find that bending stiffnesses do not change much, but torsion is affected quite a bit from the original hole-less box.
In F1, It's also relatively easy to stiffen the bending modes but the torsion has to be taken through friction and bolt shear. This matters because going over a kerb at high speed, the front corner hits first and creates a very large torsional load on the structure. If it is floppy and bends, then the suspension can't do its job to damp the load and get the tires on the ground as fast as possible. THe same idea is true more or less for a passenger car.
The stiffness of the monocoque matters a great deal. For example, in F1, in addition to the suspension loads, it has to support the nose cone and side crash structures which are supposed to crush/shatter as they gets compressed in a crash. If the monocoque is not sufficiently stiff, then the structure will buckle somewhere other than the intended area in the nose cone. The FIA does not like it when that happens. Neither do the drivers since that crumple area will likely be near where their head is poking out of the body.
If you have any experience with finite element analysis, it's pretty easy to see the dynamic effects. Just make a rigid beam with a spring/damper set at each end. Then split the beam in two and introduce a spring in the middle. The effect on the dynamic response is quite dramatic as you vary that stiffness away from the complete rigid.
