Originally Posted by
fredswain
Scale has nothing to do with it. Physics is physics. All single hole pistons are going to have a slower rebound than compression for the simple reason that gravity pulls the car down. It's effect needs to be taken into account. It is very possible that you have a situation that a slower rebound works better than a faster one. It is very possible that the opposite is true. There are some pretty standard rules when it comes to how things work but there are no set rules on what works best at any track. This is why we go to so much trouble to tune. The bulk of tuning in regards to balance can be done on a bench but fine tuning is done on a track. At this point, results are the only thing that matter and it doesn't matter if those results in the real world agree with what you already know or not. Use what works.
Fred, I'm not sure I catch your drift, but it sounds like you are talking about rebound speeds/forces with the shocks installed on the car on the track. In other words actual rebound speeds on the track vs rebound forces of a bare shock. All the graphs being posted strictly of the shocks without even springs attached.
Mattnin, those charts (if I'm reading the blue "circle" correctly) re-enforce what I previously posted. The 600 SM (SuperMoto) build is for a 50/50 type track where you are on pavement street racing half the time and would have smaller jumps than an average supercross track. Most of the time is made or lost on the asphalt so they tune more like a street bike.
The Quad showed what I would definitely set a trail quad around as that is probably the market for that shock, but I didn't look awfully hard.
The mx blue circle graph you posted has compression on the bottom half of the graph because the crank was rotating counter-clockwise according to that write up. However, they leave out secondary pistons (high speed I assume). Something worth noting as I think I stated it backwards earlier: High speed damping removes damping force, not adds to it. That chart shows what I would expect for low speed damping, approaching a 2/1 compression/rebound ratio. High speed damping would definitely put the compression softer for the same velocity as the point of high speed damping is to avoid what we like to call the "pain zone". High initial damping at low to medium compression speeds provides the response most riders look for and prevent the bike from collapsing on itself too quickly. However, since damping is not a linear function (with flexible shims trying to make it linear not withstanding) the resulting force of a high speed impact with the face of a whoop would break wrists and ankles (the pain zone) and pop the bike up, so high speed damping for such instances produces the same effect that Baja trucks have right off the bat.
Because we don't have to worry about the "pain zone" with our RC cars (unless you are marshalling 8th scale
) the non linearity of static hole pistons provides that "pack", or high speed much increased damping that we love to mess with.
Maybe that's what we need next... variable speed damping. Marcus, get to it, but I call dibs on 25%.
Anyways, done any testing yet? I have 2 races every year I attend that have very few, if any jumps and are completely blown out all day everyday. They are very old school topsoil tracks that I could totally see lower compression damping to keep the chassis low and fast through the whoops with with the increased rebound damping preventing rollovers.