Summary

00:00 - Do you consider a tube frame car a rigid body for the purposes of calculations? Generally yes, obviously we're relying on the fact that that tube frame is a well designed tube frame, there are plenty of tube frame chassis out there that are terrible in terms of compliance.
00:15 What I mean by compliance is when we load the suspension up that essentially you've got, we can think of the chassis as being a big bracket, it's the bracket that we're attaching everything to, it's the bracket that we sit on, it's the bracket that we attach all our suspension and our dampers and our springs and everything to that.
00:28 Essentially it's holding all of this stuff together.
00:31 Now just because it's a tube frame, does not make necessarily mean it's a nice stiff chassis.
00:36 There are plenty of terribly designed tube frame chassis out there.
00:40 It's really nothing to do with what it's made out of, whether it's carbon, whether it's a steel unibody or whether it's a tube chassis, that doesn't really tell you anything about the quality of the stiffness.
00:50 With all that said, generally as long as your chassis is a well designed chassis, regardless of its construction, for most and definitely for simplified calculation, things like getting your initial spring rate setup up properly, doing damper calculations, doing load transfer calculations, definitely, certainly at the entry level anyway, you're definitely assuming that to be rigid.
01:10 The reality is it just adds a lot of complexity, when you stop using a rigid assumption on your chassis, it adds a huge amount of really highly non linear complexity to the problem.
01:21 Now in saying that in a professional context you absolutely take that compliance into account.
01:24 That usually means both simulating it but also actually directly measuring how much, particularly things like torsional rigidity that you've got in your chassis, you can then take that into account in your load transfer and other simulation equations.
01:38 Obviously it depends on your levels of sophistication.
01:40 Definitely at the club level, for most people doing really simple calculations, you're definitely going to be assuming that it's rigid.
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