Weight Transfer Calcs

[scott_rfr]

I am working through making a spreadsheet to help with the suspension for next years car. Upon a closer look through Milliken I stumbled on something I am having a hard time with. I always thought that the total amount of weight transfer during cornering was only dependent on CG height, Track, RC height.

On page 587 he presents an equation suggesting that elastic weight transfer also depends on the front and rear roll stiffness. Could someone please help explain this. How does the spring rates factor into the weight transfer calculations? I am not asking for the equation as I already have it, rather why are those terms in it.

Thank you,
Scott

[scott_rfr]

I am working through making a spreadsheet to help with the suspension for next years car. Upon a closer look through Milliken I stumbled on something I am having a hard time with. I always thought that the total amount of weight transfer during cornering was only dependent on CG height, Track, RC height.

On page 587 he presents an equation suggesting that elastic weight transfer also depends on the front and rear roll stiffness. Could someone please help explain this. How does the spring rates factor into the weight transfer calculations? I am not asking for the equation as I already have it, rather why are those terms in it.

Thank you,
Scott

[Alan]

I don't have the book in front of me at the moment but I think I know which equations you are referring to. If you take the equation for front lateral load transfer and rear lateral load transfer, add them together, you get the equation for total lateral load transfer (the terms for RC height and roll stiffness will cancel out). These terms will determine how much lateral load transfer there is on each axle.

Imagine all your roll stiffness was on the front axle. You would have very little lateral load transfer in the rear (assuming equal RC heights front to rear). These equations calculate how much exactly.

[exFSAE]

Right at the top of 587..

Then the front and rear lateral load (weight) transfers due to the lateral acceleration are...

The TOTAL weight transfer from left to right, of all 4 corners, is only dependent on CGH, track, and lat g's. The front to rear split is a function of the front and rear roll rates.

[scott_rfr]

Ok, thank you I see where I was getting myself confused now. I kept thinking in terms of the whole car not individual axles.

So would this be the same for pitch centers to? So for weight transfer geometric and elastic when a car is braking or accelerating replace the roll stiffness with bump stiffness and use the pitch center instead of the roll center?

[Alan]

Unfortunately it's not as simple as turning the car 90 deg and applying the same equations. This is not an easy one to answer but page 617 in RCVD is a good start.

Its analogous in that total longitudinal load transfer is a function of mass, CG height, longitudinal G, and wheelbase. How this gets distributed between the sprung and unsprung masses will depend on brake bias, inboard/outboard brakes, antis, drive axle(s), etc... It's kind of the same, but not really.