Moment Centre / Instantaneous Roll Centre - Fully Explained (anti 56k)

[ed]

Scanned from "Circle Track" magazine October 2005 pages 20-29

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*ahem* anyway....















how to measure moment centre:
http://www.v-eight.com/tech_forum/vi....php?p=172#172

cheers
ed

[myne]

Makes me want double wishbone :/

*plans insane double wishbone ae82 conversion*
;p

[joecoolmk2]

i just brushed over that quickly, looks very technical!

so i could do this to my mx22, cuz it has wishbones? or is there more than that involved?

+rep for you ed!

[oldcorollas]

i'm definitely going to build a few models and play now
pity the yanks have this thing with only turning one direction when racing

[takai]

Yeah, the whole moment center concept is a bit lost when you have to tune for it in both directions. But it is still immensely applicable. Good work there Ed for providing that info for us.

[ed]

hehehe, id get bored driving in one direction/corner all day...

of course you can still set a car up for a circuit based on the predominant corner type. clockwise vs anti clockwise circuits etc. alt you can balance the roll centre bang in the middle and just accept the compromise.

as for tuning in 2 dimensions:

obviously the rear roll centre tends to be higher than the front

Figure 10: Roll Centers and Roll Axis, Side View



These pictures show the roll axis crossing through the car's two roll centers. These pictures show you where these items are in the car. The large dot is the rear roll center. The circle is the front roll center. The diamond is the center of gravity and the dotted line is the roll axis. This is the same picture (same idea, different view), but from the Rear View. These are the major components of the car, the two roll centers, the roll axis and the center of gravity.

Figure 11: Roll Centers and Roll Axis, Rear View



Ok, now that we can picture these major components of the car in out minds, imagine what is happens when a cornering force acts on the center of gravity. The car rotates around the roll axis with the outside of the car gaining load. Unless the cg happens to be the same height as the roll axis, then the car will not rotate at all. And of course, if the cg is below the roll axis, the cornering force rotates the car such that the inside of the car gains load. Interesting.

[myne]

Be interesting to figure out the roll centre and COG of a low weigted car like the wrx - I wonder if that's the secret to their handling?

I'm referring to this last sentence ofcourse "And of course, if the cg is below the roll axis, the cornering force rotates the car such that the inside of the car gains load. Interesting."/