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06-02-2009, 03:21 PM   #86
claude
Sidecar Jockey

Joined: Mar 2002
Location: Middleburg, Pa. (Snyder County)
Oddometer: 3,891
Quote:
 Originally Posted by Clancy Maybe I'm missing something here Claude I just read that last bit a couple of times to make sure I had read it correctly. With race cars, the aim is to get the roll centres as low as possible, generally speaking. There is always room for adjustment to slightly change handling, i.e. to induce more oversteer/understeer for a particular track or situation. But when building the car, much thought is put into building low down weight, and when ballast is added to bring the car up to a competition weight limit, it's always placed low in the frame. So why, when building an outfit, would you need to raise the rollcentre. I'm currently in the early stages of building a dual purpose rig and have been planning to put a 38 litre auxilliary tank low down, inside the triangle formed by the three wheels. Should I be re-thinking where I put the tank? Input from Richard, Phyllis etc welcome too
Many confuse the 'roll center' with 'center of gravity' (CoG). The center of gravity to put it as simple as possible rotates around the roll center .

For example When watching a nascar race you will may hear them say " they came in and raised the track bar'. In essence they raised to roll center.

With a low roll center and a high center of gravity the weight transfer in a turn is in a large arc. This translates into body roll. In most cases it is desrable to lower the center of gravity but there are definatly limits. If we are stuck on the possiblity to lowering the CoG then raising the roll center is a means to get rid of some body roll and allow the weight transfer to be in more of a lateral motion than 'up and over' so to speak.

When we determine the roll center locations at each suspension point then from there we can establish how they work together. This, in basic terms, is called 'roll couple'.

Clancy you wote:
>>I'm currently in the early stages of building a dual purpose rig and have been planning to put a 38 litre auxilliary tank low down, inside the triangle formed by the three wheels.<<
Yes, by all means do so. You will be lowering the center of gravity which is a good thing. This is different than the roll center.