hi everyone,

i'm responsible for the design of the suspension for my FSAE team. I've been working on CAD design and calculations for the past month or so and here's my question:

In RCVD, in chapter 16, there's an example on the calculations that are performed to determine the rates of the car and to help in designing the ARB. On p585, there's a detailed example and on p601 can be found the simplified example.

Also, on the OptimumG website (Claude Rouelle's company for those who know him), there's a series of .pdf files that show similar equations to choose the correct set of springs and ARB design for a desired suspension.

However, my results vary from RCVD detailed vs RCVD simplified vs OptimumG. I was wondering which one of those three set of examples yields to the most accurate values?

Thank you

JP Bahous
Suspension Manager

Well. What are your results?

What are you designing for? Ride? Handling? Cornering? Balance change under braking?

I don't particularly care what Claude, Milliken, or Smith say to be honest. If you can prove what you think is best, then so be it.

That said, run some numbers. Write a simple script in Matlab. Figure out how your balance and grip level is going to change through brake/drive/cornering. Make a judgement call on what's best.

When I first started I was getting some different results too and did not understand why. One thing that will change between your "RCVD detailed" vs. "RCVD simplified" is the addition in tire spring rate in roll stiffness distribution. The addition of the tire spring rate will vary your balance during a cornering situation. Second I believe that the OptimumG defines motion ratio different than RCVD. While neither is wrong it's just preference I guess. In the end watch your units and which way you define your variables.
Each one of the three set will give you results that will work and then you can test and come up with your own theories of what kind of setup your car will need. Start simple and ONLY add complexity as you need it.

Scott Mingay
Rutgers Formula Racing

What are the variances you are talking about?

Those sources make linear assumptions about everything, and use simplifying concepts such as roll centre heights.

To me, that means they will always be 'off' from reality and therefore is they are 'off' from each other it's probably no big deal.

Comparing results for different car parameters using the same model should inform your design choices adequately. The rest you'll learn either by more advanced modelling techniques or track testing.

Regards, Ian