## What causes torsion on a car chassis?

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Just a quick question that hopefully someone here can help me with...

I am working on a project that is developing a method for determining the torsional stiffness of a carbon-fiber monocoque about the x-axis of the automobile. Despite all of the research I have conducted for this 6 week project, I still cannot seem to answer what causes this torsional force. I understand that having a high torsional rigidity is important for accurate handling. I also understand that when undergoing a turn, the chassis is torqued along the y-axis... but does this turning also result in a torque in the x-axis? Also, does the drive shaft and differential generate any noteworthy torques?

I guess what my question comes down to is: What causes torsion along the x-axis of a car chassis?

Matt K

EDIT: I defined the x-axis a the longitudinal direction of the auto
Last edited by keepreal1315 on Fri Jun 24, 2011 3:24 pm, edited 1 time in total.
keepreal1315
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Joined: 24 Jun 2011
Location: Virginia Tech and TU Darmstadt

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First, you should declare what you are calling the x-axis. I am assuming you are referring to the standard SAE definition of x being longitudinal.

Inertial forces give rise to twist in the same way they give rise to lateral load transfer. Imagine a stick figure car, with a point mass at the CG and restrained at the front and rear axles.

Lateral acceleration acting on that CG point puts a torque on the whole system which is restrained at ground. Whole idea is to have everything rigid, or significantly more rigid than the "compliance" you are intentionally building into the system - the springs, bars, etc.
Grip is a four letter word.

2 is the new #1.
Jersey Tom
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Joined: 29 May 2006
Location: Huntersville, NC

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Yea i was referring to the x-axis as the longitudinal direction.

Thanks for the quick response and great explanation. This clarifies a lot for me.
keepreal1315
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Joined: 24 Jun 2011
Location: Virginia Tech and TU Darmstadt

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sticky tires and a driver trying to wring it's neck.
There are two things in this world that take no skill: 1. Spending other people’s money and 2. Dismissing an idea.
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Joined: 2 Jan 2010

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keepreal1315,

The primary cause of longitudinal torsional strain in a chassis structure is a relative difference in the forces reacted at the F/R tire contacts on a given side. The forces reacted by tire contacts are due to inertias, aerodynamic forces, and drivetrain torques.
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riff_raff
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Joined: 24 Dec 2004

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that's what I said
There are two things in this world that take no skill: 1. Spending other people’s money and 2. Dismissing an idea.