fork tuning for enduros

Taffy said:

smorgy

when you go off at an angle you really do donchya! i can't start in the middle of nowhere again! i'm in serious need of some skiing this weekend in italy and then head down for a few weeks.

regards

Taffy

Click to expand...

Until you try listening to someone that knows more than you, you will continue to struggle...you have drilled holes in the pistons, put a ridiculously soft stack on the face of the piston, refuse to use the clicker to adjust with, run excessive spring rates, too high an oil level and are fixated on the mid-valve float...

You make it impossible to help... :roll:

Taf, Italy will do you good, if you do get an opportunity to get there, it will be good for you, time to consider stacks while skiing down the slopes in the sun, the sinful living, the mountains, the beverages, it will drain your wallet too... Or just go to the sea for a couple of hours and look at the waves and breathe the fresh sea air.

Sorry about the deflection, no need to follow mr Marzoccis example, nor my shimming madness, I think it would be too soft in the 1st stage for my taste. as I said, 3 shims minimum in the bv 1st stage for me thanks and no drilling in the bv. The mv in the zocci could be well be a very free flowing one, if so not needing any much counter pressure from the BV, no idea really what it looks like in the Marzoccis though.

While not very tactful, and in fact a little bit rude, there is some sense in ktmlews post, even if the picture makes it hard to believe, if you at some time can get your hands on softer springs they'll not mask a lot of the progress you make in the stack department as much as the firm ones will, sag is not everything. Same thing with the MV float, if you go much under .9 mm you are likely to mask the progress and everything will blur out. With the bv extra bleed holes I think you shouldn't use a too low a mv float, no harm in going as high as 1.25 I think. That not saying the .95 or 1 mm float is bad, it just needs enough pressure from the bv to operate on. Like from at least 3 off 1st stage bv shims.

If you absolutely feel that you need to have extra bleed holes then plug the ones you drilled inthe bv and drill new ones in the bc since there they do not contribute to cavitation but instead work to fight it.
And you'll still have free bleed in the bv, only it is ADJUSTABLE! Yes, that is what the clickers are, free bleed, only adjustable... Not a bad thing.

As soon as you get cavitation (from compression), whatever you do to your rebound stack will be in vain.

Regards

here's another mad stack its from zerodog on ktmtalk for a 300 with 12mm rod forks


Zerodog Flexy Backer BV stack

(2)24x.1
16x.1 (transition)
24x.15
22x.1
20x.1
18x.1
16x.1
12x.1
8x.15 (pivot / transition)
18x.1
16x.15
14x.1
8.5x.3 (2nd pivot)
12x.15(used as a washer on the base)

good to know someone is trying different things

Regards

edit there is a test of these type of stacks in

http://www.husaberg.org/index.php?name= ... 76&start=0

Good to know someone else is trying different things too... Good to know you are not the only shim stack madman in this world.
Cool with the second pivot, it makes sense.

Regards

That pic is interesting, and this discussion has been talked befor on KTMtalk. I have designed a custom Hydra-stop with a seal in it. It allows oil in but closes during rebound. It will allow any negative pressure (vacuum) to be relieved when only needed.
It closes by pressure built up against it during rebound. I did not want use a hole because I feel the real issue of cavitation is during compression only.

KaBooM

Kaboom,

Any picture of your hydra stop?

Regards

KaBooM said:

That pic is interesting, and this discussion has been talked befor on KTMtalk. I have designed a custom Hydra-stop with a seal in it. It allows oil in but closes during rebound. It will allow any negative pressure (vacuum) to be relieved when only needed.
It closes by pressure built up against it during rebound. I did not want use a hole because I feel the real issue of cavitation is during compression only.

KaBooM

Click to expand...

could be a better way to go. a BC bleed hole caused refil or cavitation problems on rebound. reducing the size of the hole (0.4mm with 16Cst) to fix that reduced the effectiveness of the hole in helping relieve negative pressure on compression something that the hole also creates sometimes but only on internet forums

perhaps oil always flows out of the hole then consider that as a hole alone flowing oil out of the cartridge on compression the BC bleed can raise cartridge pressure if BV clicker is closed and can also circulate more oil through the cartridge. who knows which is more effective valves or a hole? will have to try valves I think.

just very roughly what kind of area does your valve offer when open ?

regards

just made a jig to very roughly test fork spring rates.

20mm preload then rate tested over the next 150mm of compression

so one is very very roughly a 40 and the other a 46 in the initial part of the stroke. they are supposed to be 44s. this is on a new 08 650. going out to 200mm gives very very roughly 42/48. can't say what they would measure in a proper jig but they are definately quite different.


there is a post by Davej on TT that explains how this sort of mismatch can be used to create a softer initial rate though keep the same overall rate. he explains each spring has soft spots and these soft spots will deform first and the stiffer parts of the spring start working later in the stroke. the softer one of 2 has softer spots than if the 2 springs are of the same but slightly higher rate than the soft one. or something like that.

link to graph not really working prolly have to cut and paste it

"http://s22.photobucket.com/albums/b341/davetj123/?action=view&current=Spring2.jpg"

thought someone might be interested.

while on springs: I had a lot of trouble getting MV float under 1.2mm with the stock MV spring and the method of reducing float that is very well described in the doc. :wink: not complaining taffy , just sharing. when turning down the shoulder on the tap, the MV piston face is moved closer to the spring seat reducing the installed length of the spring and increasing preload.

its tricky to find things on Ktalk but it is described on there in a few spots that the float can also be reduced by adding small washers inside the spring so that the spring prelaod remains the same just that the shims hit their new seat earlier. this can overstress the shims apparently and some guys build reverse pyramids to support the MV shims if needed.

edit heres one http://ktmtalk.com/index.php?showtopic=279225&hl= end edits

winding MV springs from 0.4mm to 0.8mm diam wire and altering the preload showed that the MV spring seems to offer some degree of control over LS compression and "slap" felt when landing back wheel then front wheel after a flat out high speed jump or when the front wheel crests a series of whoops at full extension.

now pretty happy with no MV spring and float at 0.2 to 0.5mm I added a preload dish to the BV face to replace some of the damping lost by removing the spring. the preloading is not very good for small rocks at high speed but the preload dish was not needed with 0.2mm float. the rock problem with preloaded BV can be adressed by doing something like BV 24,12,15 24 etc etc.

removing the spring provides an excellent opourtunity to try a 12 or 8.5mm radiused MV backer which can then be easily made from a solid round bar, drill a hole though the middle 90 deg to logitudinal axis with a drill press or hand drill if you are good then drill a 18.5mm hole or file or grind to the correct depth to set up the float you want then press it onto the MV or use locktite, its not going anywhere if it comes loose anyway. just have to make sure the MV bleed holes are clear.

there are new gold valves that are 2 port configuration that would be an excellent match to the bidirectional bend encouraged by a radiused backer.

the springs from KYB and Showa BVs and MVs are a nice soft spring alternative to the very stiff and evil WP MV spring.

to test the degree of damping provided by the spring leave it out.

regards

Bushie

old soft WP MV spring. 0.6 diam wire, compressed 3 mm high, uncompressed 10 mm.

new WP spring is 0.87 diam wire but wound to similar size and turns.

KYB and showa springs are 0.48mm wire, less turns than the WP springs bit still softer. they fit on my stock MVs ok.

removing the evil heavy WP spring at 0.7mm float made the forks very very compliant over nasty rocks and even bigger chop was less tiring due to loosing the "slap" at full fork extension.

unfortunately the forks did not hold up in the stroke for slower speed full stroke events.

lowering float to 0.2 with no spring improved holding up the stroke but I wanted more so I preloaded the BV face shims. moving the damping provided by the MV spring to the BV also reduced extended leg HS cavitation.

the effect of dish preloading or 1 or 2 degree tapered face preloading is described with graphs and big words and stuff in the penske document linked earlier in this thread.

its quite simple to do even if it sounds complicated, put the BV in a lathe, machine a 0.05 or 0.10 pocket in the centre to diam 10mm or so then draw file nice concave dishes over the compression ports. concave from centre to edge. alternatively and possibly easier do as the penske guys did is to machine a 1 or 2 deg taper into the face.

smorgy has a pic of a dished rebound face in his gallery. ring shims can also be used to add preload, they are a ring shim of about 24mm OD, 20mm ID or so and 0.2mm or 0.15mm thick, a normal 0.1mm thick 20mm OD shim locates this ring.

alternatively you could just bend the edges of the second face shim away from the BV face under the comp ports.

I went too far I think with the 0.1mm dish, 0.05 would be better.

now at 0.5mm float, no MV spring, 0.1mm BV dish preload to hold up the stroke in slow speed full stroke events and 2 shims under the first 24 to let it blow off if I hit a rock.

0.1mm preload BV, 24, 12, 15, 5x24, 14, 22, 20, etc etc

its pretty good I think, just the 12 alone was not enough room for a blow off adding the 15 was better.

say you have a MV stack and put an extra shim in, its gets stiffer but also increases spring preload, take out a couple of shims softer stack and less preload so the 2 work together. lower float / more preload works together too but there may be a point with low float where increasing MV spring preload has a negative effect.

the turning point on my forks using the method in doc is about 1.2mm float. On the softer WP spring in 14mm rod forks I'm guessing its about 0.95 or 1mm. but thats only a very wild guess.

So if you want a lower float but its getting harsh over small rocks and starting to "slap" at full extension and won't dive down enough in the corners, reducing spring preload or using a softer spring should help without having to soften the BV and lower the cartidge pressure. If that was a problem.

of course there are many ways to skin the cat and still have the same result

regards

Bushie

0.1mm preload BV, 24, 12, 15, 5x24, 14, 22, 20, etc etc

Click to expand...

this is good for rocks but looses too much LS. it sucks real bad for whoops.

adding oil helped hold up the bike with a softer MV, more oil seems to make the BV more effective, but given the Bvs already have a dish instead of removing it I tried some bleed shims.

0.12 dish, 12x0.1 bleed or better 12x0.05, 7x24, 14, 22 etc. clickers fully closed.

all bleed flows over the stack perhaps easing transition from bleed to shim lift. as with Taffy's BV holes! something good about them after all and they probably help with the refill issues in the 14mm rod forks.

LS portion of stack still carries some preload. good enough for me on rocks and still enough LS.

anyone done any work on how to translate a good 14mm rod BV stack to a 12mm rod Bv stack?

a rough control volume analysis of the flow rates and subsequent pressure drops due to differing rod diameters through BV and MV gives about 2.22 times stiffer Bv needed for the 12mm rods. degree of accuracy implied by 2 dec places is ludicrous 2.0 +/_ 10% would be better I guess.

looking at the stacks and ride descriptions where cavitation has been ironed out it seems about right that a nice pressure balanced 14mm rod fork BV needs to be made roughly a bit more than twice as stiff to translate to a 12mm rod BV to retain proper pressure balance. problem is perhaps that other non tunable factors in the piston designs such as seal lip length and turbulent port entries make the 12mm rod forks harsh when attempting to translate this balance. perhaps thinner oil is a way around the harshness without compromising pressure balance.

regards

Bushie

problem is perhaps that other non tunable factors in the piston designs such as seal lip length and turbulent port entries make the 12mm rod forks harsh

Click to expand...

Maybe a forum is not where to discuss things, it often leads to arguing rather than discussion, but could it be like this?: Shim deflection would be more dominant an effect, considering the lower deflection of the 12mm rod BV stacks than it would on the 14 mm rod BV stacks where the shims deflects farther away from them. If the bleed is done with a bleed shim the distance at LS is increased and the effect giving a less harsh LS than drilled holes in the 12 mm rod BV ports?
Edit: You would have to compensate by shutting the compression adjuster quite a bit for the extra bleed from the bleed shim. If the bleed shim is too thick you run out of clicks for the fine tuning and will need a thinner shim.

I just realise I could have formulated this a lot bette.

Taffy, I can't believe how much bleed you have in the BV. Drilled 'oles (3 off dia 1.5 mm?) and a little bleed stack as well. The 'oles drilled probably flow cavitates less than the flow through the clicker would have, if you had it, so maybe they feel more smooth after all?

Regards

Taffy.

Aaah, the rake, or lack of it! and front wheel more loaded. It's not the same chassis geometry as on my old banger. Taffy, I was thinking you had gone astray using that heavy forks spring. It just does not compare, does it. Sorry I did not really trust your judgement to the full regarding the springs, but it makes sense, provided the chassis geometry is taken into account. You used the shorter wheel base frame didn't you?, and not the "chopper" frame.

Regards

Re: RE: Taffy.

Taffy said:

yes quite correct smorgy. i even reported the difference from the pre '03 frame to the latter and sure enough a heavy fork was a little lighter. put it this way, before i changed the frame i kept talking of .46 or .47 springs but after the change i dropped the subject.

also please remember that the springs are working harder with the damping to help the compression and not help the rebound! the bleed is to get 'dip' back on braking and entering! (into corners).

regards

Taffy

Click to expand...

OOH yeah. I'm using proper eibach .46 springs. weigh only 70 Kg. .48s would not be too stiff based on the ammount of preload I can put on these 0.46s for beach runs/ dunes/ high speed whoops and the extra force it provides.

I reckon the front springs are more dependant on the bike and chassis than the rider weight. and the rear spring is more influenced by the rider weight than the front spring.

going from .46 to .48 is what 0.02kg per mm. an extra 6Kg mid stroke and 12 at the end when x2 for 2 forks and its SFA or a knats or a bees watchmecallit particulary when taffys 30kg heavier than me.

biggest advantage is toward the end of a heavy braking section before a slow or smooth corner particulary downhill where fork rod speed starts to get very slow. if there is no rod speed then there is no damping force. even if the MV is almost solid its not going to help. oil height maybe but we both run "excessive" oil heights compared to some. with stiffer springs I can go much harder into braking and pull a lil stoppie just on corner entry and be just bottoming where before I would have slammed into the BC. less wallowing on downhill runs, its all good. for LS dip i use the front brake and a soft MV spring instead of a drill.

some posts mine included make Taffy seem a fool. sorry taff . KTalk is great for some things but a husaberg is not a KTM and needs different advice. how many of the Ktalk veterans have spent any usefull ammount of time tuning a berg? only took a couple hunderd hours tinkering and testing to realise it. while I still don't agree with taffys huge ammount of BV bleed its only casue it don't work in my bike with different rod diam and funny MVs.

I drilled 6x2.5mm oles in my BV last week. they are still there!! I'll put up a pic its not what you think.

Keep it up Taffy, theres 2 mad hatters at least!


regards
Bushie

Hah- haaaa!
That's supension for ya!

Very humbling indeed...

this may be of interest

http://www.thumpertalk.com/forum/showth ... p?t=682886

possibly requires the use of smart performace vmk 215i alien snake oil to be effective

looks like trying to keep the actual conversion cost right down so without making new Mv stems or smaller port BV's its limited to using a very soft MV blowoff spring and a very stiff Bv blowoff spring, can't see any backfill ports.

might be cheaper than NOST, who knows which is better?

regards
Bushie

link to penske doc in begining of thread isn't working its attached below. hope it works

hey lads
bushy & i have been having a bit of a yap about the pros & cons of a preloading stacks.
thought we might go public for anyone how has interest in the subject.
as i have not had any experience in comparing one with one without its hard for me to comment.the way i see it from the sidelines,is a preloaded stack on rebound might not be a bad idea, but a preloaded stack on compression sounds to me as though it would be rougher the 1st part of travel.i'm thinking it should be the other way around,a bit of dribble from an unloaded stack might engage the stack slower resulting in a smoother ride the 1st part of travel.don't know could be wrong?
i'm pretty happy the way the compression is at the moment,certainly better than stock & certainly better than me mates 07 husky 510 which i rode around the same track.in saying that you never can have too good of a suspension right?
i done something a little out of the square on the bv,mainly cause i had a lack of shims,i know most add more shims to the bv then alter the mv to suit.i think?
i thought to myself why not just remove the 2x10mm .3's altogether ,which in turn gave the shim less limit to flex till it hits the 18mm .2mm at the end of the stack.i also put in 2 x 22mm.1 's free bleed shims at the piston face.thought this would be stiff as buggery,but in combination with the new mv stack it is quite good ,suprisingly good.
can anyone see a problem with this set up?
as it is now
bv ----- mv has zp3 mod
post ---- post
18 .2 ---- 2x 8mm .3
12 ---- 24x.15
14 ---- 14
16 ---- 16
18 ----- 18
20 ---- 20
24 ---- 22
24 ---- 24 .1
24 ----- 24 .1
22----
22----