fork tuning for enduros

Taffy · Nov 21, 2007

Taffy said:
smorgy

another thing: if you let all the oil go up through the MV, when you need all your suspension in a g-out: all the oil is above the MV and therefore you get fork lock quicker surely? but this small amount of oil never gets a rest and must cavitate.

if we use the BV more there will be more oil on the outside of the cartridge/around the base of the leg and little above the MV. so now it won't bottom out and so we can add more oil (in order to get to the fork lock at max travel again - i hope you do the same?). more oil cavitates less. also i believe that fork lock may be coming early with the cavitation and therefore we can afford oil above the MV on a g-out because it isn't all frothed up and therefore this will allow the rebound to work better.

what i'm saying is that there might be oil; permanently above the MV that never makes it back down, this will keep the oil in better condition and less cavitation - sharing the work so to spreak!

so: softer BV, harder MV = room for more oil = more oil (120-110 air gap?) = no cavitation = better rebound?

how does that sound?

regards

Taffy

here you are smorgy!

it's midnight, my eyes are red but i've found the info i discussed with you in a PM. it turns out that it was me that thought of it! god i'm old! and senile!!

regards

Taffy

ktmlew · Nov 21, 2007

Taffy-the cartridge is ALWAYS full of oil. Doesn't matter how stiff you make the mid-valve, unless you lock it out with no float, it does NOT push oil through the base-valve. So the mid-valve build has no effect on how much oil height to use.

You need to separate all the variables and then add them back as needed.

In order, comp first...
1. Clicker/piston bleeds holes
2. Base valve stack
3. Mid-valve ck-spring
4. Mid-valve stack
5. Mid-valve float
6. Air spring
7. Spring

For rebound:

1. Rebound Stack
2. Spring
3. Air-spring
4. Clicker
5. Piston bleed holes

The rebound bleed (clicker) effects both comp & rebound.

So you CAN build a fork with a check-plate set-up (no "mid-valve") that works pretty darned good for one type of terrain but isn't as well-rounded for different conditions. Basically a Race-Tech type deal. Fairly stiff base-valve stack, slightly stiffer than optimum spring rates with more then optimum preload and high oil level...

Actually this is probably the best way to learn what you NEED. Build it really basic with a single stage stack and then add a mid-valve which will require you lighten the base-valve LS ( maybe add a crossover), reduce preload as it won't need as much if forks stays up in stroke due to the mid-valve, reduce oil height as again you won't need as much "damping"...

It's like a crossword puzzle. You have to use ALL the pieces.

Smorgasbord · Nov 21, 2007

Yes, you can have a massive oil leak and still ride with useful fork function, as long as the 4 holes at the bottom of each cartridge are still covered with oil, they will not suck in air. The cartridge will breathe oil in and out trough the holes as the fork telescopes, the amount of oil corresponding to the piston rod displacement as it moves in and out of the cartridge. And so the cartridge will always be full.
(Exeptions are rare, probably only noticeable during "Free Air Rebound". But there will still not even then be AIR inside the cartridge. Possibly microscopical amounts then, but their effect will be just as microscopial, not really worth mentioning.)
Regards.

Taffy · Nov 22, 2007

well i never actually said that the cartridge wouldn't be full of oil. i may have misunderstood or don't understand the inner functions completely BUT i know that when that oil goes through the BV it goes out of the cartridge and up between the cartridge and the lower leg. the more that oil goes through the bottom the more will rotate around and come back through the 18cm mod. it also means that on the rebound there is plenty of oil going back and through the BV.

as i understand it, the oil is compressed between two pistons and will take the route of least resistance. if it all went upstairs we'd have fork lock sooner rather than later. if a lot more went through the BV we wouldn't have enough going through the MVpistonrebound set up, it would be over worked, cavitate and lose control at the end of the rebound stroke.

i'm trying to utilise every nook and cranny in the fork leg. nobody runs 110mm air gap even though that's what the book recommends. freudian slip? dreamland? hardly!

i used to get fork lock on 140 air. now i bottom out on 120 air. the difference is that i've stiffened the MV a lot. whereas the BV is back roughly to where it was about mid spring last season. it was soft - not that i knew this!

i'm simply keeping this in mind and following it to see where it leads.

i hardly dare disagree with you lew about the MV having no effect on oil height....seems to me that with everyone changing their oil level/air gap that something is slightly different between each bike....

regards

Taffy

ktmlew · Nov 22, 2007

as i understand it, the oil is compressed between two pistons and will take the route of least resistance. if it all went upstairs we'd have fork lock sooner rather than later. if a lot more went through the BV we wouldn't have enough going through the MVpistonrebound set up, it would be over worked, cavitate and lose control at the end of the rebound stroke.

Pour you favorite beverage in a mug full to the top. Stick you finger in it to the hilt. The amount that runs over is the same as how the base-valve works. Very small amount of oil flows through the base-valve. You use the phrase "if it all went upstairs" like it exits the cartridge? Oil doesn't "squirt" out both ends of the cartridge unless the du bushing at the top is worn out. Maybe I don't understand your description? Easy way see it...set your oil height and then re-check it with the cartridge rod fully extended, tubes collapsed. Difference is rod dispacement. When you are moving the rod by hand how is the oil flowing? Through the clicker bleeds ONLY. Stacks are irrelevent.

Oil height is a spring. Period. How much spring do you need? The amount the oil level will "raise" due to the cartriodge rods displacement is deteremined souly by dimensions of the rods dia and is NOT valving related. If you built a really stiff mid-valve stack with NO float, a plunger style fork, then YES the cartridge would be emptied on every stroke. But we don't do that for woods use.

The biggest problem I see with home tuners is they try to use too many tricks. I am NOT a big supporter of the ZP3 tap mod as it requires a major re-work of the mid-valve. You don't see ANY suggested stacks for them around? The only way to find the sweet spot is to do ONE THING AT A TIME. The means after you mod the tap then keep working with the mid-stack till you get back to where you started. But no one seems to do that. They do the tap mods, change springs, base-valve stack, drill holes all over the place and wonder why it isn't wonderful first crack out of the box.

Taffy · Nov 22, 2007

i just can't agree with that lew. the oil goes through the free bleed as you say and it goes through the three MV compression ports due to the available float.

i look at the commnt of "what i'm saying is that there might be oil; permanently above the MV that never makes it back down, this will keep the oil in better condition and less cavitation - sharing the work so to spreak!" as being incorrect from august this year. it won't happen.

what i'm saying is that it's not just the oil displacement through the BV due to the rod entering the cartridge, oil leaves becasue the downward thrust of the piston creates pressure and it will go out the bottom coz it wants too not just because the cartridge rod is creating it. i quite imagine that in the top corner there is aeration which 'farts' it's way out via the bush in the top out cup (eventually).

so i think we're still in control a little bit of what goes out the BV compared to the MV.

the "lock" i talked of at 140mm that is now 120mm is 20mm different. that represents about 30cc of oil per leg difference. i want to know why ktm/husaberg/wp suggest 110mm all the time and what i have to do to fit another 15cc in there to reach the 110mm 'magic number'?

oil height is a spring. period. totally wrong!
the air gap is the spring not the oil. oil won't compress. if you meant by default more oil = less air and a ramp-up in late travel compression then we are still on the same page of this book!

i still wanna know about "110mm" and about where that 30cc went. know that and i'll understand some more. BTW i've never heard of the katoomytalk legends talk of this. so they either know better or my brain has taken me into an area much undervalued.

regards

Taffy

Smorgasbord · Nov 23, 2007

i still wanna know about "110mm" and about where that 30cc went.

Still in the bottle?

Edit:
Maybe the 110 mm is a WP-fix to cure cavitation they get because the original MV is too stiff having no flex gap for the shims? Thus being a Check Plate...

The MV stack can flex on the modified tap on the left, can't flex on the stock tap on the right.

Taffy · Nov 25, 2007

well i changed the BV for todays ride. unfortunately the track was very wet and i ahd been on the piss last night so i wasn't really with it for two sessions. nope! come to think of it - i was never with it!

my old BV:
24, 24, 13, 24, 24, 22, 20, 18, 15, 11, [email protected]

new BV:
24, 14, 24, 24, 22, 20, 18, 17, 16, 15, 11, [email protected]

the suspension was like velvet yet with plenty of feel. it sucks up everything and i can only feel anything over 6-8" tall and even then i don't feel the bump i only acknowledge a change in the pitch of the bike.

as for those rollers (woops) well it just sucked them up and went across the top of the lot with me still in control. the danger became the mud not the bumps as the speeds were quick.

unused is just 1" which on such a slow circuit is what i need to hold back.

BUT, there is always a phucking rub with all this isn't there! i'm not 100% sure but the bike seems to sit higher and on entering corners i would miss the corner and ride over the berm!

so is it worth going to a stiffer MV and soften the BV instead so i get the same effect but the pitch of the nose would be lower?

i fancy taking out the 16 and 17 from the BV. then
MV: 23, 23, 22, 20, 18, 16, 14 can finish with a 13. float will be .95mm. (i only have 14, 16, 18, 20, 22 in smaller MV sizes).

the other thing i could do is drill another three bleed-off holes in the BV piston?

if i stiffen the MV i wonder if i'll use less travel as the cartridge empties a bit of extra oil out? be interesting to know!

went with mate chris who is now registered here as 'cranksnapper' but has yet to post. he has a chris hockey (dr. shocx) set up and it was way poorer than mine. his bike sits it seems almost 4" lower than mine. it can't be true of course but i had to raise my inside leg higher on corners.

I'm going to look into getting the equipment together to work on my rear shock. it is now the area that needs the work doing.

regards

Taffy

Smorgasbord · Nov 26, 2007

Taffy,

The BV controls two things, a good portion of the compression damping and a good portion of the cartridge pressure.

The pressure drop created by the MV during compression can never exceed the total cartridge pressure. Instead you get cavitation.

The air gap pressure is added to the BV created pressure and makes the total cartridge pressure.

Regards

Taffy · Nov 26, 2007

well that makes my mind up then!

the suspension is again "just about there!" but i need to swap (british spelling is swap yankee is swop - i believe) a BV out and a MV in. that way i'll hopefully keep that air gap of just 120, smaller float that they like on k-talk of .95mm and get all this right.

i'll pull the 17 on the BV and add a 13 to the MV. i think it might make it a little stiff on HS but i may in that case (on the day) pull the 15 for a 14 in the BV.

if i get anything like the suspension i want and the nose is still a little high well then i may drill some more bleed off holes in the BV piston or could enlargen the ones i have from three x 1.1mm to say 2mm.

your opinions are always appreciated but i think i need to show willing here with ideas.

ZP3 did a weird test on k-talk in which he literally used just one shim in the MV and did a BV stack = unrideable. he then did a test where he had only one shim in the BV stack and had a full MV. the bike was actually not tooo bad. this brought him to the conclusion that the BV can't flow enough oil through the compression ports. i know that PMK has and does i think still use delta shims there and several of them have ported this the lower piston. anyone with anyviews on this porting? other than to go buy NOST or goldvalves etc?

and although this is a fork thread, i want to gather info on a nitrogen charging set up? non-ktm? how far would a schraeder (correct spelling) valve stick out?

we had a KIWI dealer here once reckoned he had the shortest and best valves anywhere!

regards

Taffy

Smorgasbord · Nov 26, 2007

If you have to drill more holes, don't enlarge the 1.1 ones. I think that a twice as large a hole will flow 16 times more. Better to drill more of the dia. 1.1 ones.
Better yet, Drill them as the one in the picture and plug up the ones you made in the BV:

Then they can not contribute to cavitation as your BV bleed holes do. Why?, simple, If the MV tries to drop more pressure than available then the flow in these bleeds will diminish.
How is that for an idea?

There are shrader valves on my car that are looking really good. Not like the ones on the wheels. If I took them the freon would leak out and contribute to the ozone hole though.

Regards

Taffy · Nov 26, 2007

smorgy

well i'm struggling to see any holes anywhere! i take it that this is the bottoming cones and the red and green dots represent drillings? as this is a threaded area i would have to drill the BC and the cartridge while in line and bolted up?

under compression i think that the oil wouldn't be sucked up and through the piston. i think that the top of the cartridge would 'feed' off getting air or is it oil or a mix (WTF?) through these tiny holes rather than valving the oil itself. on the rebound it would try to displace some oil back out through these holes but i trust that wouldn't be such a big problem!

of course you could find a shim/washer, even chip the top of the cartridge so the Bc doesn't close as far, drill and test. if it fails you pull apart, file the cartridge smooth round the top and the two drilled holes wouldn't align? so back as was.

one up the b^% no harm done!

what do you look for it to acheive - jsut stop the massive zero in pressure at the top of the chamber? is that what causes it?

what WOULD go through the holes on the compression stroke? oil? if it's air and we get thatin the top of the cartrdige we will be riding with an ever increasing pillow of air till the oil on the outside of the cartridge is all the holes would see and the air would be 'self-levelling'.

what size ar you on about?

why are you looking at me like that?

my name isn't mr G. pig!!!! or is it? bloody hell it is!

LOL!!!!

regards

Taffy

Smorgasbord · Nov 27, 2007

Taf,

It was not easy to find the two specks... But yes, they are actually there and specks is what they are.

The drilled hole is in the picture, above the bronze bushing. The BC is sectioned right through along its length. But I guess if you want you could just as well drill right through the thread or possibly through the cartridge cylinder right under the thread where the piston seal does not rub. If it must be plugged, beacause you drilled too many, then put a rivet or M1 screw in them with a nut and loc-tite.

The pressure drop created by the MV during compression can never exceed the total cartridge pressure. That is why the flow through the holes is on your side all the time.
When you approach cavitation the flow in the bleed holes stops, since the pressure is gone, stolen by the MV.

(Free bleed holes in a BV in the same situation will make cavitation more likely since they drop the total pressure a bit since they don't stop flowing.)

If I take the Shraders out of my car AC the dumped freon will contribute to global warming and the AC will be good to have but it will not work without the freon. If the Shrader valves are left in place they will retain the freon and the AC will work. But since there will be no global warming I won't need the AC...
A breaker would maybe sell similar Shrader valves cheaply?
Regards.

ktmlew · Nov 27, 2007

Anyone tried a Showa style stack on the ZP3 tap, maybe something like this?

(3)24x.10
(2)20x.10
(2)17x.10
(13x.10
tap

Taffy · Nov 27, 2007

smorgy

it hit me as i looked at the diagram. i see the thing now...there's nowt as blind as those that WILL NOT see!

Smorgasbord said:
The pressure drop created by the MV during compression can never exceed the total cartridge pressure. That is why the flow through the holes is on your side all the time.

how can a drop still exceed something? weird!

When you approach cavitation the flow in the bleed holes stops, since the pressure is gone, stolen by the MV.

don't get it? i thought cavitation might be happening during the compression and not rebound?

so surely it's: "when you approach cavitation the bleed holes draw oil in since there is a vacuum?

are we on the same page here? i take cavitation to be when oil has gone through a hole violently and due to not being able to fill a given space quick enough the oil has gassed itself with N2 (or summink?)???

what do you take it to be?

Lew
i can't even spell showa! so i have to take it one step at a time. everything here is covered in muck and the only place i can practice is at a circuit at weekends. covered in shyte i don't want to sit on the bike let alone change stacks. in the winter, progress is slow!

your float gap idea gets closer and so does a 13 pivot shim at the BV base.

regards

Taffy

Smorgasbord · Nov 27, 2007

The word exceed can also mean "go beyond" (a limit). The limit here is the total cartridge pressure, the MV pressure drop during compression can never exceed that. Nature will not have negative pressure.

i thought cavitation might be happening during the compression and not rebound?

An opinion shared by many, me included. But then during rebound the fork must refill both rod displacement AND the two mutually exclusive tasks; refill cavitation and perform rebound damping. It will be harsh.

so surely it's: "when you approach cavitation the bleed holes draw oil in since there is a vacuum?

Well, yes, maybe, at least when you have actually reached cavitation they'll get some oil pushed in, which is a good thing. The flow in these holes will always fight cavitation, the flow is always on your side, so to speak. That is why I still am so tempted to start drilling.

are we on the same page here? i take cavitation to be when oil has gone through a hole violently and due to not being able to fill a given space quick enough the oil has gassed itself with N2 (or summink?)???

what do you take it to be?

Same page, in a way. Cavitation, I think, is any formation of (a) hollow(s) or void(s) in any material. Violent flow through tortous paths, whatever that is, would surely cause cavitation, narrowing the path of flow, depending on how violent the flow is and more if the absolute pressure is lower.
No gasses are necessary for cavitation, the volumes of solved gasses in the oil are probably microscopical anyway. We are talking about air and oil here, not CO2 and water.

Showa? do they use 0.11 shims like Kayaba do, as it turned out that they actually did. There is a considerable difference in stiffness between 0.1 and 0.11 shims. Nothing you would believe when looking at the small difference in thickness.
No, I have never used the ZP3 tap anyway. Tried a wire ring but it made the MV so weak I didn't like it.

Regards.

Taffy · Nov 27, 2007

Smorgasbord said:
Nature will not have negative pressure.

o yes it does!

it's called a vacuum!

don't you drill a thing yet lill fella!

when the bike goes into compression the shim stack and the free bleed are letting lots of oil through. there is plenty of oil there for rebound. the piston is drawing up oil as it rebounds but it's not a suction - it's just a void. oil needs to be going up a smaller tube than 26mm or whatever to get decent suction.

what concerns me is that very top area, you know, under the BCs? you want oil in there all the time beecause on the rebound the oil has to be thick and deep to act as a resistance.

so what you really want isn't a drilled hole in the top corner but a one-way valve just permanently letting oil in.

so on compression the oil drives up through the free bleed, through the MV and then we have a trade off!

on the one hand we have real suction up in the top of the BCs which helps draw oil upwards and through the MV HARDER. however if you drill a hole up there the oil will come in through the top hole and just mean that the oil was pushed down with no suction effect upwards by the cavity in the top of the cartridge.

of course, and you may have a point, the right kind of drilled hole will just 'top up' a bit with every bump dropping oil into the top of the chamber. we need oil over shim stacks though to gain control of our bikes. TH once told me that if he could close all the adjusters and use 7.5W he'd be very happy.

EVERYTHING DONE 100% ON SHIMMING!

anyway, oil collects in those bottoming cones so you need that resourse and not a drilling to the side. oil must sit waiting to fall through.

why not find a very tiny CF reed and place it right near the top of the chamber so it lets oil in but not out? how about this one then! a real ABC! you know the game battleship? the little reds and whites. fat knob on the inside of chamber dangling down and inside. everytime you hit a bump the head drops open and the whole lets more oil in. on rebound the whole blocks with the extra oil in and the MV is going back up through solid oil with oil having nowhere to go but through the rebound stack.

you could then start to reduce the rebound shimstack what with all that solid oil in the top!

regards

Taffy

Taffy · Nov 28, 2007

wanna PM me smorgy?

regards

Taffy

Smorgasbord · Nov 30, 2007

Nature will not have negative pressure

Should have said: Nature will not have negative absolute pressure.

o yes it does!

it's called a vacuum!

If it's negative it is just a difference between two pressures, a relative pressure. Gauge pressure can be negative because it is the relative pressure between atmospheric pressure and measured pressure. If the pressure measured is lower than atmospheric then it ends up on the negative part of the scale. Relative pressure can be less (negative) or more(positive) than the pressure you compare it to. The absolute pressure can not be negative even if the vacuum is very good.

when the bike goes into compression the shim stack and the free bleed are letting lots of oil through. there is plenty of oil there for rebound.

MV stacks, right? its the pressure created by the flow resistance in the BV that pushes oil through the MV as the MV moves down through the oil. With too much in the BV of free bleed and too weak shim stack during compression there might not be enough pressure to push enough oil through through the MV to completely fill up the increasing volume above the MV. You do not ever want to get there because this is cavitation. Only if this does not happen there will be plenty of oil for rebound. The BV must provide pressure enough to guarantee that there is oil and not a void (froth) above the MV. If the frothy void forms, what you have is vacuum since there is no air in this part of the fork.

what concerns me is that very top area, you know, under the BCs? you want oil in there all the time beecause on the rebound the oil has to be thick and deep to act as a resistance.

Very true, I think, and that is what you normally have unless the BV is too weak to create the pressure needed to push enough oil up through the MV to keep the area filled with solid, thick and deep oil.

so what you really want isn't a drilled hole in the top corner but a one-way valve just permanently letting oil in.

No oil will enter this way if the valves are balanced. There will be pressure here both on compression and rebound. Only if the fork starts to approach cavitatation the oil will enter this way because of the pressure drop. And you would not normally like to get there anyway. But if it happened it would surely help rebound a lot as there would be oil pushed in there through the valves for it. But you'd still benefit from having the bleed hole in the BC rather than in the BV since it would not rob any valuable pressure where it is needed, would keep you farther away from cavitation so this would be on your side. That is provided you WANT a free bleed for the slow speed movements.

so on compression the oil drives up through the free bleed, through the MV and then we have a trade off!

The hole is the free bleed. It works on compression as well as on rebound. But it does not lower the BV pressure and that is the point. If the pressure above MV drops the bleed hole flow drops too because of that pressure drop. Which means no loss of pressure that otherwise would would have been pushing in more oil through the MV.

on the one hand we have real suction up in the top of the BCs which helps draw oil upwards and through the MV HARDER.

You have no more suction than 100% vacuum. Can literally not suck any harder than that. What you need is more pressure on the other side to push harder. But if you drilled the BV you are bleeding out some of the oil that would have contributed to creating some of that pressure

however if you drill a hole up there the oil will come in through the top hole and just mean that the oil was pushed down with no suction effect upwards by the cavity in the top of the cartridge.

If there is a cavity in there with no oil in it or no air in it there will be suction beacause in that cavity you have vacuum.

of course, and you may have a point, the right kind of drilled hole will just 'top up' a bit with every bump dropping oil into the top of the chamber. we need oil over shim stacks though to gain control of our bikes.

Yes that was the whole point.

anyway, oil collects in those bottoming cones so you need that resourse and not a drilling to the side. oil must sit waiting to fall through.

Well, collects.., I'd say they are totally submerged in oil all the time and there will be oil for you when needed. The drilling does not puncture the actual bottoming cone itself, that would not have been good for anything.

why not find a very tiny CF reed and place it right near the top of the chamber so it lets oil in but not out? how about this one then! a real ABC! you know the game battleship? the little reds and whites. fat knob on the inside of chamber dangling down and inside. everytime you hit a bump the head drops open and the whole lets more oil in. on rebound the whole blocks with the extra oil in and the MV is going back up through solid oil with oil having nowhere to go but through the rebound stack.

you could then start to reduce the rebound shimstack what with all that solid oil in the top!

Absolutely! With all the solid oil in the top the rebound can actually do its job. On compression you can have the oil pushed in through some custom reed or battleship valves that you have to invent or have it pushed in through the MV by the pressure created by the flow resitance through the BV. That is why you would not like to weaken the flow resistance through the BV because you would weaken the pressure created by it, which would otherwise have helpt pushing in solid oil up through the MV to be used later for the rebound damping.

regards

Taffy · Nov 30, 2007

well that means to me that the simple bush in the BCs should infact be a seal? i'm convinced that although we have oil submerging the BCs from above and a full chamber below, we need to maintain the high vacuum and pressure figues in the top of the MV and the best way to do that is to have a seal on that 2" bush running through the BCs.

THAT IS WHERE PRESSURE IS ESCAPING!

i once damaged a cartridge rod and gave it a bit of a clean, i wish i'd replaced it and the bush in the BC. i can see no harm in a small 1mm bleed INTO the cartridge. it'll really help the rebound.

maybe that's why i haven't cupped any shims yet? coz i have a dodgy leg!

BTW it's not a quality to right incomprehensible science. i have already reported you to the "speak plain english" society and it's chairwoman, 89 year old nora bloodthirsty is on her way around to see you!

have a nice day!

tonight i've done the following
i have removed the 16 and 17 that i put in the Bv.
24, 14, 24, 24, 22, 20, 18, -, -, 15, 11, [email protected]

beefed the MV with this 13 so:
23, 23, 22, 20, 18, 16, 14, 13
so the float is now 0.95mm

the idea is that i'm back to as was before last weekend (ok i have gone from a 13 to a 14 splitter on the BV) but have now got a HS 13 in the MV and a smaller float.

i can add 15cc of oil from here and put anything on the Bv i want. not sure when i'm out though...

regards

Taffy

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