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# Calculating Double Wishbone Suspension Loads

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## Calculating Double Wishbone Suspension Loads

(OP)
I wonder if someone can help me.

I am trying to calculate the loads in the suspension components of a typical car double wishbone setup. I have found a thread on the www.fsae.com forum, which seems to be exactly the kind of thing I am looking for

http://www.fsae.com/forums/showthread.php?11179-an...

(See Post 5)

Which involves considering the assembly as a 3D truss, and building up matrices, containing 1. the unit vectors and cross products at the mounting points of the struts at the upright and 2. the forces and cross products at the tyre contact patch. Which when the inverse of matrix 1 is multiplied by matrix 2, results in a third matrix containing the loads on the struts.

What is the general concensus of oppinion of this meathod? Obviously it is quite simplified as few wishbone setups have components which are purely in tension or compression.

Can someone give me the name of this method of truss analysis, and any textbooks / resources that specifically cover this method?

Thank you in advance for your help!

### RE: Calculating Double Wishbone Suspension Loads

My opinion is that if you can't work it out by drawing 4 free body diagrams, one of which is trivial, you probably need another job. The matrix method is a sensible way of formalising it but adds a possibility of further mistakes.

Cheers

Greg Locock

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### RE: Calculating Double Wishbone Suspension Loads

(OP)
Thanks for that BUGGAR, I appreciate it.

Vectors do appear to be the way to go with this, I'll have to spend a bit of time studying your .dwg file

### RE: Calculating Double Wishbone Suspension Loads

Thanks for the download tip. The .dwg file is for some development stuff I'm doing - putting a V8 into a Lotus 7 replica; the Gen V Camaro IRS should be a natural.
I like using vectors because I can figure the loads as I draw the parts.

### RE: Calculating Double Wishbone Suspension Loads

Hi vftm,

The only correct method is the 3d vector approach since most of the "inplane" methods fall into pieces when a suspension is a 5 link multi-link (without any wishbondes). I have written a few topics about suspension design on the FSAE forum so have a look there.

Cheers,
dynatune

### RE: Calculating Double Wishbone Suspension Loads

Vectors make it easy to find your roll center/fulcrum point/moment center or whatever they're calling it these days.

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