Lateral weight transfer

[The Stigg]

Hello,

in order to understand and analyse the dependencies of the most important parameters influencing the vehicle car dynamics, I started do programm my own computermodel of our car. And as intended the lateral weight transfer is the most important one.

So I took a closer look at the equation for the lateral weight transfer (Race Car Vehicle Dynamics: page 682). And know I'm a little bit confused because:

1) The lateral movement of the RC haven't been taken into account. This movement definitely increases roll while the lever arm on which the tyre forces are acting increases. And additionally the Roll axis will also move lateraly (yaw).

2) Adding lots of caster on the steered axle (and a lot of teams do this) will increase roll because of the differences in vertical movement of the inner and outer contact patches. This has also not been taken into account.

So what do you think about these points?
Should I consider them or are the influences too small?
How do you calculate lateral weight transfer?

Thx

Andy

[The Stigg]

Hello,

in order to understand and analyse the dependencies of the most important parameters influencing the vehicle car dynamics, I started do programm my own computermodel of our car. And as intended the lateral weight transfer is the most important one.

So I took a closer look at the equation for the lateral weight transfer (Race Car Vehicle Dynamics: page 682). And know I'm a little bit confused because:

1) The lateral movement of the RC haven't been taken into account. This movement definitely increases roll while the lever arm on which the tyre forces are acting increases. And additionally the Roll axis will also move lateraly (yaw).

2) Adding lots of caster on the steered axle (and a lot of teams do this) will increase roll because of the differences in vertical movement of the inner and outer contact patches. This has also not been taken into account.

So what do you think about these points?
Should I consider them or are the influences too small?
How do you calculate lateral weight transfer?

Thx

Andy

[flavorPacket]

wheel dyno?

[C.Zinke]

Hi Andy

1) The "Position of the RC" is a theory, that is not useful for this detailed analysis. You will see it when you make force based analysis of the geometry

2) Calculate your lateral load transfer, caused by your steering geometry. Then decide if its worth to worry about it


In my Opinion RCVD is a book, where you can get a good overview of suspension technology. But unfortunately it is not that scientific. Furthermore there are often assumptions that are not correct in every application. Especially the calculation of roll rate isn't that good in RCVD


I looked for a big adjustment of the lateral load transfer, without influencing the roll stiffness. My front axle can be adjusted to get between 37% an 58% of the lateral load transfer, without influencing roll stiffness.

[The Stigg]

Hi C.

thx for your reply!

Nice to hear that other think about this in the same way.
Could you plz tell me which literature you are using?

I think that looking for other alternatives in contolling the lateral weight transfer is one of the keys to success.
Our car will hopefully have an active anti-roll-bar, but we'll see. http://fsae.com/groupee_common/emoticons/icon_wink.gif

Andy

[C.Zinke]

Hi Andy,

i think mechanical understanding is the key to suspension design. If you like a book that discusses some mechanical behaviors i would read.

Prof. M. Mitschke "Dynamik der Kraftfahrzeuge", Band C Fahverhalten"

This the German title, but i am sure it is available in English.

On Topic:

What do you mean with: "I think that looking for other alternatives in contolling the lateral weight transfer is one of the keys to success."?

Christopher

[The Stigg]

Hi Christopher,

"Wie gut dass ich deutsch kann!" Danke erstmal für die Literaturangabe.

There are several ways to control or influence the lateral weight transfer.
1)Just think about the effect of caster I mentioned before or the weight reset belonging to KPI.
2)It is also possible to influence it with anti-squat or anti-dive geometries (change of caster with droop or dump, and the vectors of the load paths acting on the suspended mass).
(This seems to be the way you do it on your car, right?)
3)But I think the simplest way is to change the roll stiffness by using anti-roll-bars or good RCH-control etc. like many other teams do. By using this method you are gaining less dependencies between the important parameters and so you are able to control them.
The next thing to think about is the dynamic attitude of dampers, springs and tyres. When you are using a geometric method (1&2) of controlling the lateral weight transfer what do you think will happen with your vertical tyre loads while driving on a bumpy course?

Andy