Chassis design to reduce torsional strain

[mike]

we know that torsion is create via a moment arm hence the distance between the dampers so is it likely that we could design a car with reduced or eliminate all torsional stress to make the stress on the car pure bending?

[CMSMJ1]

I've read that a few times Mike, but I cannot figure out what you are saying..

You talking basic chassis rigidity?

[mike]

haha im sorry

im basically asking people about designs that can reduce torsional stress other than reducing the length of the wheelbase

all i can come up with to put the push rods at the same point so torsional stress will be zero


edit:
For example we put 2 wheels on the front and rear of a motorbike, while will have non-independent suspension it will have close to zero torsional stress

[xpensive]

Location of the push-rods would not have any effect on torsional load when this comes from unequal load on the wheels.

[mike]

so the wider the track the less weight shift but with a larger moment arm so to accelerate in a circle at given acceleration there will be and equal torsional stress?

[Jersey Tom]

Well.. no. Chassis loads arise from inertial forces. Given the same CG height you will the same inertial rolling moment, a wider track will just resolve this moment into less load transfer from left to right.

Chassis load is gonna be there regardless.. and stress generally isn't your critical design parameter, it's strain. You can minimize chassis strain by developing a good design with smart load paths.

[autogyro]

Very good advice JT and often over looked even by those who should know better.

[mike]

so allow me to answer my own question..
lower CG height = smaller moment arm ratio = less torsion = less strain


i should change this topic to strain, i was really asking is more toward. 30,000nm/deg vs 60,000nm/deg how to end up with the same angle of twist while maintaining the same wheelbase

[Jersey Tom]

It would be helpful to know what exactly your end goal is.. or why you're going after all this.

[mike]

basically im trying to know how to make longer chassis as strong as shorter chassis

given same wheelbase same tracks same torsional rigidity im looking for ways to reduce the twist so that we can go back and chassis can be made lighter
i.e less load put through the chassis

i know people would all say good design gives good torsion rigidity but what about reducing load to design a lighter chassis?

[Jersey Tom]

If you want to reduce load.. drive slower! You're always going to design to place the CG as low as possible so that's not exactly a design variable.

Gotta watch your terminology though. Is STRENGTH really the issue? How many times do you see a chassis fail from overload? I've never seen it, even in FSAE. Well.. that's not true. I've seen a rocker mount shear off, but that's a separate story.

Really.. it comes down to smart design and using material efficiently. That's how you take weight out. With regard to wheelbase.. your vehicle dynamics engineers are gonna drive that one. If a few inches extra wheelbase give you an advantage and it costs you a pound or two.. so be it.

[xxChrisxx]

eliminate all torsional stress to make the stress on the car pure bending?

Last thing you ever want is bending. For a spaceframe, everything should load up in either tension or compression.

And if you want a longer chassis to be more stiff, triangulate everything (within reason), make the chassis from more (ie shorter) box sections. All this adds weight, so the key is the get the compromise.

In general, larger section tubing with thinner walls handles loads more efficiently than smaller section and thicker walls. EDIT: (Up to a point where the tubing could collapse or buckle).