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# Sway Bar Design - Heat Treatment

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## Sway Bar Design - Heat Treatment

(OP)
I am fabricating a rear sway bar on a race car. My question is related to what type of steel to use and the appropriate heat treatment to specify.

I was planning on using 4130 - 1.25"O.D. x 0.095 wall

Would 4140 or 4340 steel be something to consider.

Based on my stress calculations, I need a bar that will end up with a yield point of 167,500 psi.

Thanks.

### RE: Sway Bar Design - Heat Treatment

Zandor20,
With stresses that high, I would consider using something other than 4130.  What is the length of the bar and how much twist are you expecting?  As you already know, it would be nice if you could use 4130 since it is inexpensive and available in many diameters and wall thicknesses.

-Joest

### RE: Sway Bar Design - Heat Treatment

4340 hardened to HRC40 will give you a UTS of about 190ksi. Yield will be around 180. Suggest that you include a test piece when you go to the heat treaters, send it out for material testing to be sure.

### RE: Sway Bar Design - Heat Treatment

(OP)
From arm to arm it is 26", with around 9.4 degrees of twist at one end.  I am planning on using 10 to 12" arms right now.  All calculations assumed 10" arms.

### RE: Sway Bar Design - Heat Treatment

Zandor20,
What is the diameter - OD and ID?

### RE: Sway Bar Design - Heat Treatment

(OP)
1.25" O.D. x 0.095" wall

### RE: Sway Bar Design - Heat Treatment

Using the numbers you provided and the formula Tmax = T*r/Ip with Tmax = max shear stress, T = torque, r = radius, and Ip polar moment of inertia, I come up with a max shear stress of 56ksi at 9.4 degrees of twist.  What formula(s) are you using?

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