Torsional stiffness.

[hemipanter]

Question concern a race car construction. The chassis that is a tube frame could be looked at as built in 4 sections.
Front suspension, engine, driver, and rear sections. Each having their own triangulation. Totally the chassis show a 30000Nm/dgr reading over the suspenion pushrod rocker location points. Each section show different readings and some areas like in between the rocker and A-arm mountings at the same axle is tremendously stiff.
The question...what effect will this have on the behaviour of the car? Would the car react to anything but the total stiffness over the measuring points? I am not discussing cracking or impact effects etc.
The reason I ask is that I heard opinions about the matter.
Regards
Goran Malmberg

 

[GregLocock]

The shock absorber is the most sensitive to the torsional stiffness. The shock absorber 'sees' the point impedance at which it is mounted. This is measured in units of mm/s/N, typically, and is a function of frequency.

For handling purposes we are probably interested in the frequency range 0-10 Hz.

The distribution of stifnnesses, and masses, and spring-mounted masses, in the vehicle will alter the shape of the impedance graph, but may not have much effect below 10 Hz.







Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[hemipanter]

Thanks!
Goran