On 7/7/07, Mike <[EMAIL PROTECTED]> wrote:
Thank you. I get soooo frustrated with people saying that a bike should have a low CG. At the recent Ann Arbor Green Fair I mentioned to a guy that when I put the new Yellow Tops in my bike they had to go in a little lower than the old Hawkers and I felt that had ill effect of the handling. He tried telling me that a low CG was good and that my ill handling must've come from somewhere else. We went back and fourth a few times before he got angry and stormed away. That was a very strange interaction.
Hi Mike, I've had the same discussion. It's hard to win. I heard a saying once that went something like, "Be careful what you learn - it's very hard to get it out of your head if it turns out to be wrong." I think the problem has to do with the fact that everyone thinks in terms of objects that are stable when at rest. In that case a low cg certainly enhances stability. But a motorcycle is one of those rare beasts that is inherently *unstable* at rest. That single fact changes everything. A monotrack vehicle requires constant active stability control (provided by the rider) to remain upright. By definition, the more "stable" you make it, the less "responsive" it is. A balance must be struck. There is a broad, continuous spectrum between "more stable than a train on rails" and "as quick to change direction as a squirrel on crack". The proper balance depends entirely on what you're doing. A 300 mph Bonneville bike wants stability, but plan on smacking that pothole rather than swerving around it. A motard set up for go cart tracks will thread a needle at 10 yards, but take it out in traffic and a sneeze will put you into the oncoming lane.
I have not read Tony's book yet - can't find a copy at a reasonable price - so I'm pretty ignorant, admittedly. However, I have a theory that the CG location is a ratio of rake, trail and tire diameter.
Maybe, but I doubt it. So much comes into play. Moments of inertia about all three axes, attitude change under braking, suspension quality, tire profile, etc., etc. Hardware evolves. When I was on a Superbike team (back when leather drive belts were the latest trick) a 26 degree head angle was considered incredibly steep - because the frames and forks were so flexy. Any flex would be interpreted by the tire as a steering input. I think people find out the hard way what works and what doesn't. That understanding needs to take into consideration what the specific application is and the state of the art in hardware at the moment. Chris
