fork tuning for enduros

The_Force said:

I just did my sags and they were front 600-560-530 so static 40mm, rider 70mm .
(i mesured from front axle to front fender)
on the rear it was 705-680-610 so static 25mm, rider 95mm

are these sag settings ok on the forks :?:

Regards

Click to expand...

Cross overs or transtions.. A topic of much debate...

So before we can even begin to delve into such topics we must first set-up a frame work.

Defintions, or such might be a goood place to start:

Cross over fall into two major groups:

Independent Cross over:
Independent Crossover is the type you have just listed. 12mm for example in a stack with a 24mm face shim. The gap the shim produces must be bent over by the 24mm shim before the shims bellow contribute any more resistance to further deflection.

NON-Independent cross over:
This is less comon type, and I belive to be the most usefule. What happens with a N-independent is the OD of the crossover is such that the shims above the crossover apply force and subsequent deflection over the whole bending moment. The only diference being that the deflection rates are in diferential to the design of the crossover. Inother words we could configure the crossover to increase defelction rates when you are fartther into the deflection range.


What Independent crossovers acomplish is a lag in force force both from a time and from a absolute force consideration. What really happens with your base-valve forinstance is the oil flow through the fixed orfice (clicker) reaches a flow threshold. The fluid flow meets signifcant resistance at some speed, based on setting, then ar that point you feel resistance until the shim stack starts to open at this point the damping force rate of increase actually slows. Now the rate stays nearly constant until you've crossover the transtion. The valves area growth is not limited beyound the effective spring rate of one shim. Once the crossover has been deflected over the shim stacks stiffness is increased and subsequent valve area growth is limited by the effect of the other shims. The rate increases again.

If you look at transtions on a instantontainus level the time factor of the design is also important. When we have a independent crossover imagine if the force of the impact acting on the wheel is signifacnt enough to cause a large deflection at the shim stack. The shims must actually bend the distance to create the area required by the flow. The fluid is meet with little restiastance relative to the area required until the cross over is closed. Where this matters is say some square hard ripples with little wheel movement, so flow volumes are not signifacnt but flow speeds are. (I'm convinced thats why some riders build this type of set-up and go its great! when the over all performance may be horible.)

The major issue with a Indpendent cross over is the fork confuses the realtionship of force and time, and can create a very two faced feel. Imagine the rider cannot percive the subtle diferences between one bump or load and another effectrively. When the rider incounters one bump it may not cross over and the area of the valve does not produce signifacnt damping force, the riders go WOW that was awesome! Then a second later another bump with a techincally slightly diferent shape produces a bigger flow volume and speed and the rider gets the bars ripped out of her hands... That leaves the rider going what just happened? Subtle diferences create massivly diferent valve area requirments, Independent stages creat large areas in the damping force curve where subtle speed ranges create the same effective valve area...

Now... One more improtant detail. Shim defelction is limtied to a realtively small value, depending on piston design. Lets say we have a piston design that will create .35mm deflection at the piston face to create maxiumum valve area based on our rod daimter and its "highes" speed. This stack must control the entire range of valve area growth effectively. (That depends on a lot of stuff well leave it simple for now). So we place a .1mm indpendent transtion in the stack. We just gave up one third of our total defelction. Now to control the addtional area growth we must effectly stiffen the portion below the transtion. However paradoxically, when we stiffen it we create a signifacnt change in the deflection/force realtionship. The fork feels much harsher right after the transtion with only a small increase in speed..



Ok.. So this is a lot for anyone to digest. The important thing to rember is that all designs have a compromise, what feels good may feel horriable somewhere else. What all tuners must do is create the smallest posible compromise, regardless of what may feel best in a VERY narrow circumstance. When typing this out its amazing how hard it is to say anything without putting a case into it as all the set-up paramters impact the outcome of the design. Its very easy for me to see why forinstance a "low flow piston" is so critical to our cause.. But anyway thats a whole other case..

Click to expand...