08 fork shim stacks

spent a couple of hours playing with an assembled cartridge with BC bleed in a big water trough.

water is different to oil and there is no way this testing replicates what happens when a 650 berg has to slow from 90 to 20km/hr over 30 or 40 1 to 2 foot deep braking bumps. probably several orders of magnitude closer to the truth than using air.

But, its fun and someone might be interested to know what happened.

first observation is that a lot of water comes out of the DU bushing. similar to that expelled by a 0.4mm BC bleed.

second looking at the lack of movement of face shims on the BV there is no way that you can replicate the speeds and forces at work while riding. unless you may happen to have devoted your life to rapid to and fro movements of a small diam slippery rod.

does water come out the bc bleed and the DU bushing all the time the rod is in motion? NO. even with an unaltered rideable cartridge BC flow can be reversed.

just for fun I changed BC bleed sizes, built different BVs and MVs and tried to force cavitation. a very soft BV and a stiff MV will reverse flow through the BC bleed on compression. with a fair bit of trial and error I found the turning point and could alter the parameters with the BV clicker.

again this is in no way a conclusive answer to efectiveness of a BC bleed as its not in the bike hammering along over nasty bumps. But its good enough for me to continue with the idea of a BC bleed and was lots of fun.

other possible anti-cavitation advantages of the bleed include circulating more of the oil to help dissapate heat, perhaps purging of any emulsifed fliud and of course any closing of the BV clicker raises cartridge pressure.

there are significant disadvantages as cavitation is now possible on rebound. call it refill not keeping up or whatever you like it produces the same thump on compression after a rebound event.

if you don't believe in cavitation then you must be happy right? so just stay happy.

I don't care if its cavitation lack of refil, poor recovery charachteristics or an ancient gypsy curse bestowed apon poor Wim Peters' family years ago. the less of "it" that my forks have the better they work and the faster I go. KYbs with 32mm cartridge bores 430mm long on the same bike to not have "it". they can tolerate a softer BV, stiffer MV to hold up in punishment without being harsh and still not have "it" I'll hazard a bet showas wouldn't either.

comparing to the KYBs theWP cartridge is only about 390mm long and has approx 28mm bore, the mid valve piston is a hydrodynamic nightmare and too thin to allow smooth flow on compression, the refil path through the BV is also rediculously turbulant and restrictive. these things can be improved.

with every reduction in cavitation oops i mean "it" the rebound becomes more effective and needs a couple of days to sort out, usually 3 or 4 stack changes to get it right.

3-4 days a week average has been 6-7 days/ week the last 2 months. Pretty sure that i can tell the diference between too much/too little rebound and "it". the forks can exhibit both charachteristics if agrivated long enough, the tricky bit is pin pointing which is which.

but thats just for my bike on my track with me on it, except for the water trough thing which is for no bike, may not apply or be even noticable to anyone else. if your happy with the forks then lifes good.........no? fancy some showas? or an ohlins TTX cartridge to put in the WP pasta utensils......

have fun on the bikes

regards

Bushie

wow!

you have been a busy boy!

i hear what you're saying but this has been a lot of work to prove very little?

not everyone is getting cavitation - as you say! but i did and now i don't - i think?

shame that hole in the BC isn't one-way only?

keeep up the good work sir!

regards

Taffy

yes it proves very very little, I just wanted better forks by doing some shimming....................... that was in november.

very dissapointing mr WP but how do you know when to stop? the more you do the more is wasted if you give up? is putting showas or KYBs on giving up?

BC bleeds need to be one way yes, making small check valves like a grease nipple with a softer spring.

other option to jap forks is homemade TTX or 40mm cartridge ID. I like the idea of a bigger cartridge ID. like using a bigger hammer.

regards

Bushie

Bushie I just did the same test inside a clear tube with a WP cartridge, pistons, mid valve and rebound and base valve assembled to my specs, comp clickers set, rebound clickers set with 5wt oil all set as per ride parameters and the oil definatley flows from a BC bleed on rebound as expected and on compression as many don't believe. I could show photos but that proves nothing (anything short of video probably won't convince some) so I'm not sure what is wrong with your test. (I see now you went out of your way to create the reverse with a stiff mid and light comp). I was taught that this was the case and now I have just demonstrated to myself that what I was taught is correct.
As per an earlier post, if your BC bleed sucks, your forks will suck. Trying to control the flow with one way valves is not the way to go in my opinion, you will create more problems than solve.

To follow on I then did the same test with clickers at extremes, both out and in with the results the same.

relevance?

Hi Danger,

as we both know this type of testing cannot replicate what happens in the bike. even the most expensive dyno in the world can't yet repeatedly replicate speeds over full strokes we know from telemetry that our bikes are subjected to over full stroke HS hits.

there is nothing wrong with your test as there is nothing wrong with my test. we tested different things. you showed that it is not possible to replicate cavitation by hand and hence the BC bleed flows out all the time. my test showed the same thing but I went a step further and found what happens to flow through the BC bleed IF cavitation occours.

to get the flow to reverse with a rideable cartridge just move the rod (compression direction) slow enough that the MV does not open, simple. that simulates cavitation.

playing with the stacks not the clickers alone shows the same thing only it takes some fiddling to get the balance right. the point is that if cavitation is not a problem then the BC bleed will not help. if it (cavitation) is a problem then the bc bleed does help.

the situation is subjective and depends apon many variables in terrain and the bikes.

unless the test replicates cavitation it does not test the positive aspect of BC bleed function. I am not strong or fast enough to replicate extreeme agrivated cavitation by rapid hand movements with a rideable set of stacks.

as for the flow on the bike it all hinges on whether or not you can get the forks to cavitate. mine are almost cavitation free and I'm probably being much too fussy but you must agree that if cavitation occours then the BC bleed will help. even if flow does not reverse in the bike, a bc bleed helps in other ways.

how will the one way valves create problems? surely if oil always flows out of the BC bleed as may be the case then the one way valves will show that there is no difference in having them in or blocked off?

If I hadn't put the KYBs in to test how they handle extreeme aggrivation and played with the stacks in them I'd have to say that WP forks are good enough for anyone. I'm being very fussy remember. i"ve been quite happy a number of times but comparing to the KYBs the WP forks do not hold up as well against extreeme aggrivated cavitation.

no one is right or wrong really, the goal is to have nice forks is it not?

regards

Bushie

quick edit, just tested with 0.4mm BC bleed now I'm happy :twisted: :twisted: :twisted: , the cavitation on compression is acceptable unless pushed to danger ously high speeds in braking and the negative aspect of the BC bleed, cavitation on rebound, is nearly eliminated.

thanks for making me do that test Roo, it was fun playing in the duck pond

I was taught that this was the case

Click to expand...

Keep testing for yourself not copying others....

Click to expand...

?

none of this flow stuff really matters, end result is a good set of forks for Bushies bike. nobody has ever paid me for suspension work and I am not an expert in suspension, just very fussy. I test almost every day have different bikes and forks to compare and am quite mad in bursts, not at all consistently fast enough to win stuff, thats different.

Within the normal valving parameters this chamber is always in positive pressure.

Click to expand...

maybe it is, so just a thought that at least someone with experience could be nice enough to give us a set of stacks and setup info that define "normal valving parameters". something positive and helpful anyway.

Its great fun learning about these forks and very challenging. they have provided the steepest learning curve of any forks I have ever mucked about with. nice one Mr WP.

cheers!!

edit

further to the above rediculous pissing match, one way BC refil ports benefit "normal valving parameters" by allowing extra oil into the cartridge when needed. they improve the forks ability to handle aggrivation.

check gallery for pics.

regards
Bushie