Anyone has good handle on how bike geometry works, what affects what and how to approach bike setup, or maybe links/sources to read up on that? I know it's a complicated subject, I'd like to just get some basics down. Looks like some late model Ducs had some issues that required changing the triple but people also had success with changing rear ride height instead. My application is a supermoto racer (CRF), I will try some shorter offset triples but some people seem to have success with just jacking up the rear and dropping the front with stock offset, same thing as with Ducatis. It's hard to navigate this being a newb and lots of guys who race SM's came from MX so their idea of how the bike should handle on pavement is pretty strange to me. My bike with stock geometry doesn't want to turn for shit and also likes to push the front evey opportunity it has. Dropping the front end seem to help but I haven't tried anything radical yet since the forks won't go up more than maybe 6mm without some handlebar clamp spacers, and there's no easy way to adjust rear height. Seems like the real solution is to both drop the front some, jack the rear up some, get shorter triples and maybe even shorten the swingarm but again I have no idea what I'm talking about, just going off of what others have said. All of these changes are pretty good $$ since rear shock is not height-adjustable, new triples are $400 etc. so I'm looking for a plan on what to look for and how to attack the problem. Thoughts, opinions?
Oh yea and before someone suggest it, I do climb all over the front of the bike as much as I can so it's not the issue with sitting back on the bike too much. The feel from the front end is not confidence-inspiring too on pavement, gets a bit better with dropping forks but not enough to start pushing it, I know it can be a lot better than that on a 230lbs bike with super-soft slicks.
Is it chattering yet? What tires are you running? Try giving Walt Schaefer a call. He's been around a while and knows a thing or two about supermoto tires and setup. His shop # is (256)538-5906. He's a michelin distributor if you didn't already know. As far as changing the fork or shock height, rate, etc... it isn't as hard as you might think. A competent suspension shop should be able to do it. However, if you don't know where they need to be, the shotgun approach generally doesn't work that well.
It chatters allright, I dropped the suspension off to our local tuner though who seem to at least have a good handle on what to do with springs and hydraulics so this should get taken care of. To add to this I'm only 140lbs so most people's handling issues seem to be a bit different than mine. I'm running 465 or 497 front dunlops and 497 or 950 rears, 16.5 front. Not sure it's cool to just call someone without giving them some business.. But thanks for the reference!
For what it's worth, my CRF supersingle chattered to some extent regardless of setup until I braced the frame. Hopefully you can find an easier solution to your problem.
the rear on a duc is very adjustable, 10s and 10s of mms worth of adjustment but, in all that range there is a narrow window just 5mm wide. get inside that window and you can do whatever you want to the front. get outside it and no amount of front-end adjustments will cure handling ills. i imagine a similar situation exists on other brands.
Turn in is largely a function of rake and trail with F/R weight bias tossed in, but you retards, I mean motards, ride dirtbikes with sky high ride heights, so the height of the center of gravity has to come into play as well. Swingarm angle (seems to me anyway) to be a compromise between finding space in/on the chasis for the shock and linkage and finding room for the engine in the frame. I know the less chain pull (on the swingarm) the better, but I don't think that has much bearing on your original question because chain pull should be pretty much out of the picture right at turn in...(I think anyway)...
the swingarm angle has more to do with the driving force. if it pushes directly at the center of gravity, there's no pitching the chassis. above the CoG, the nose will be pushed down and vice versa. add the effect of the chain drive relative to the swingarm pivot and you may squat the bike. taking that into account, you have to weigh the difference in drive squat with the drive force to the CoG. different size sprockets will effect both. ducs offer a lot to play with to get it right, or horribly wrong. i couldn't be bothered to get to anal about it considering everything else there is to deal with.
Dmitry you might give GP Suspension (the Oregon shop) a call, might be an interesting project for Dave w/his new measuring machine. You guys could get the measurements of the bike and then work out what's going wrong and what an ideal (mathematically) would be, then try it out. He might be willing to work w/you for free on the basis that if he can solve the problem, all the northwest SM riders will probably want the solution.
Great idea, thanks! I'm buying up some parts to have adjustability where it will likely be needed, and then it's game on. I'm far from being the only one with a CRF SM bike and some people have stepped up with their setup info so I might be able to nail it..
