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Old 06-03-2009, 05:13 AM   #94
just another dummy
phyllis's Avatar
Joined: Apr 2009
Location: creswick, victoria, australia.
Oddometer: 88
Roll Centre.

Keep at it Boys, we'll get there yet.
Andy is almost completely right! Claude too!
Trailing arm suspension systems do have a roll centre, and it is situated at ground level!
The centre of gravity of the average motorcyle-sidecar combination (rider included) is very high off the ground, and, as in the german textbook, it is biased toward the motorcycle, not centered within the "tipover lines"(the contact points of the tyres joined by three lines to form a very skewed triangle) Trikes and the new Can Am Spyder have a centrally located C.of G. within a symetrical triangle, and are equally stable turning left or right. Sidecars are, as we all know, prone to roll over, rather than slide, especially when turning towards the chair.This a consequence of a narrow track (relatively speaking) and a high C.of G. close to the tip over line under the bike.
Anti-roll bars (to apply their tecnical name....sway bars to the general public) do just that, they resist roll, or the tendency to load the suspension on the outside of a turn, and unload the suspension on the inside of a turn,or in other words to oppose the "weight transfer" to the outside of a turn. If over done this is like having no suspension, so any bump will cause the wheel in question to lose grip and slide, and if it grips again could cause a "highside".(Is that what you meant Claude?)

The Roll Axis of a car is a line joining a car's forward roll centre (usually above the ground with modern types)with the rear roll centre, and the inclination of this axis determines how a car will behave in a corner, understeer and oversteer are the terms usually applied.
The car blokes don't know how to deal with us because we have a two track device with only one wheel on the "other" track(the right, for europe & USA, left for OZ & UK)
We still roll, just like a car, but there is no "other" front wheel to support the front corner, so if we over do it turning away from the sidecar, we are in danger of draging the nose of the chair on the ground just like McCardigan's BMW above. [Which looks to have the sidecar axle lined up with the fwd edge of the rear wheel rim (about 9" perhaps?). A bit more lead wouldn't have hurt. IMHO.]
It's getting late, must go, more sermons later. phyllis
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