maybe one of you two can tell me so that i can say if i've had it. this is the sound or feel smorgy ok!!!!!!
Taffy remember I'm no expert and most of this you will understand allready I'm including a bit extra information for others who may not. Smorgasboard has explained the cavitation and possible BC bleed function in helping to reduce cavitation in your big fork thread. even after reading that thread a number of times I did not understand so it might help someone to hear a different and perhaps more simple explanation that does not have to be filtered out from 18 pages of high tech arguments.
Cavitation feels harsh so you immediately think oh righto that area needs softening, when actually it should be stiffened on the BV. thats simple if you go soft enough on the first stage with enough bleed some lower bleed/shim resonance
may come into play and mask cavitation as stiffer springs and drilled bcs may also do. I'm not saying your forks are all wrong and or cavitating I'm on the wrong side of the planet to make any judgements its just a thought that some of the mods
may be masking cavitation to some extent.
fixing cavitation with the stacks or masking it with other parameters may be the same thing. who knows which path results in a better fork?
It seems that it’s possible to partially fix cavitation and not be aware that it is in fact still occurring meaning that although harshness is reduced or near missing, rebound is still not functioning properly and the fork is more mushy on compression to rebound transition than without cavitation. So instead of going soft on the BV it might be an idea just an idea!
to start with far too much damping on the BV a really soft MV and reduce the BV from there so at least you have a fair idea cavitation is gone. Thats my next angle anyway, you're the boss!!! and very happy with your forks too it seems :wink: it may not result in a better fork to go that way for you with your parameters but it might with mine and thats all I know at present.
I had trouble working out what this cavitation caper was all about, so I put in a really soft BV like Taffys but in my 12mm rod forks thats quivalent to about 1/2 as stiff has his, wound the Compression clicker right out and put a really stiff MV in with 0.7mm float, just an experiment that showed what extreme cavitation is like. the MV face shim was really badly cupped after a quick ride.
My bike makes a series of creaking clicks from the forks moving in the triple clamps, same sound as when you hold the front wheel beetween your legs and move the handlebars side to side or do a violent stoppie over some small bumps. it makes this noise even when I can't feel any harshness through the bars but the noise goes away when the BV is stiffened more and then the rebound starts to work better and everything is a little bit smoother yet again.. thats just my bike though..... on extreme cavitation I can hear a noise like hydraulics with air in them on an old machine thats not been used for a while.
Getting someone to video the bike over the type of bumps that were a problem and playing it back slowly was the only way I could tell if I had severe HS cavitation or packing.
I find it useful to think of oil flow in volume and displacement rather than pressure differentials
the cavitation suposedly occours on the compression stroke as the too soft BV lets out more oil from the cartridge than the incomming rod displaces.
this itself is not harsh provided the fork does not blow through the stroke and slam into the BC.
The harsh bit happens when the wheel starts to move away from the bike, the rebound stack is now in a void of air or vapour.. whatever.... say a 50mm long portion of the cartridge without oil in it on the upper or rebound side of the MV piston so it (the piston)offers no resistance to wheel movement (away from the bike) and pushed by the springs it violently slams its way through the void in the cartridge and into the oil.
thats why a bleed hole in the BC may help stop cavitation because it
can let oil
into the cartridge on the same
side of the MV piston that is pulling a void. ideally the bc hole should not be needed at all but
during a cavitation event the BC bleed can help whereas a bleed hole in the BV just lets more oil out from the WRONG side of the MV piston making cavitation worse. Even if the BC bleed does not let oil into the cartridge during cavitation it may prevent it occouring at all because it allows you to close the BV clicker a bit and further raise cartridge pressure.
In a partially cavitating fork you may not notice any harshness at all but the smoothness that results from going even stiffer on the bv is very nice. I think its because partial cavitation may induce bubbles making everything the MV tries to do on transition to and from both rebound and compression, very mushy in comparison.
with every reduction in cavitation, both partial and extreeme, rebound becomes more effective, just one indicator for unbelievers in cavitation that strange forces are at work. note my first attempt above, where I pulled shims from the BV and lowered float on the MV thereby making cavitation
worse says I need more rebound than the stock stack, and in a later post after reducing cavitation I have too much HS rebound with the stock stack.
edit1: the sudden movement of the piston slamming through the "void" on rebound may then induce partial cavitation on the compression side of the MV piston which would then be felt as harsh on compression. edit2 playing with the BC bleed made me realise that refil problems or cavitation on rebound are just as big a problem as cavitation on compression. crossing a 1 bike tyre wide 200mm deep rut at 90 deg at high speed shows this up as a harsh thump as the wheel hits the other side. as opposed to hitting a small bump on flat ground where caviatation on rebound is not induced. end edits
I wasted the first 1000km on my bike waiting for the forks to break in…they never did, they always sucked because they were trying to suck (cavitation). Should have just got into it after 500Km or so.
regards
