shim shuffle - KTM WP forks Part 2

Joined
Dec 9, 2000
Messages
129
Likes
0
#1
Servus,

This is the sequel to the thread 'shim shuffle - KTM WP forks' with new experiences,ideas and questions. For reference and starting points see part #1 under
http://dirtrider.net/ubb2/Forum24/HTML/001153.html

DISCLAIMER: Do not attempt to use any of the following as suggestion or even advice to setup your own suspension. This could be dangerous and lead to serious unhappiness with your forks. Just take this as what it is: the irrelevant babble of a curious Austrian.

While waiting on my shims to arrive an Öhlins PDS shock from MH-Racing (thanks Mark) found the way onto my KTM – an investment worth any penny! But while the Öhlins is a great improvement over the 'not so bad' stock WP shock, the problems of the fork still persisted. Finally my shims arrived and in a last minute decision I decided to use the following stack # 1:

24x0.1 3x (plus one)
12x0.15
22x0.1
20x0.1
19x0.1
17x0.1
14x0.1
13x0.1 new
12x0.1 new
11x0.1 new
18x0.3 base plate

and an oil level of 140mm. Note, that the overall height of the stack remains unchanged (13,12,11x0.1 replace stock 10x0.3 clamping shim)

The difference was amazing, but not in the way I expected it too be.

.) Bottoming from large jumps was reduced, but not as I had hoped. Still, this is not surprising as it has been stated before on this forum, that this type of bottoming is more a midspeed thing. Do I have to modify the midvalve now?

.) Headshake was unaffected and still there so I just installed my Scotts and forgot about it. This thing (Scotts steering damper) should be considered as 'live saving' equipment on KTMs !!!

I was able to reduce headshake to a minimum with very fast rebound settings or lots of static sag, but both of this actions caused other way more negative effects.

.) On the positive side, the bike was much more stable now. I could go straight through the worst acceleration and braking bumps or little whoops where before I was fighting the bike to go straight. There was no deflecting, but the ride was tiring. Great setup for plain MX-use and a probably slightly heavier rider.

All in all I liked the way the bike handled now, just a tad too much HSC for my general purpose use. Nevertheless, I was in 'experiment' mode and wanted to know if the increase in diameter on the clamping shim from 10mm to 11mm made such a difference or if it was the increased HSC. Easy enough, I left the stack like it was and just added the 'old' 10x0.3 clamping shim on the bottom.

This is the stack #2 I tried the next day on the same course, almost same conditions:

24x0.1 3x
12x0.15
22x0.1
20x0.1
19x0.1
17x0.1
14x0.1
13x0.1
12x0.1
11x0.1
10x0.3 new
18x0.3 base plate

Holy s**t, what a difference. The bike almost felt like at the start. Pleasant and nice, but unstable and hard bottoming. I had to go in on the comp clickers from 12 before (stack #1) to 6 come at least into the range of the lap times with stack #1.

Well, I need some explanations! This 10x0.3 shim made so much difference, but why? Is the increase in overall height (the shims can bend more till they hit the base plate) or the reduced diameter (from 11mm to 10mm) responsible – or is it a combination of both??? Is this actually a 3-stage valving with the base plate being a SHSC (super high speed comp) 1-shim shim stack?

At least I know now WHERE I want to be – somewhere between stack #1 and #2. Ideas include a thinner (0.1 or 0.15) 10mm clamping shim or a thicker (0.15 or 0.20) 11mm clamping shim. As I only have a 11x0.15 at hand right now stack #3 will look like this:

24x0.1 3x
14x0.15 a little more LSC still
22x0.1
20x0.1
18x0.1 a little less LSC to compensate for the 11mm clamping diameter
16x0.1 ditto
14x0.1
13x0.1
12x0.1
11x0.1
11x0.1 makes for 11x0.2
18x0.3 base plate


Michael



------------------
 

marcusgunby

Lifetime Sponsor
Joined
Jan 9, 2000
Messages
6,450
Likes
2
#2
Do you ned the base plate shim on the RFS?On the 125 there is no lead on the bottom of the tap so there is no need for a bottom plate shim.Dont forget the last shim sets up the shim stack strength for the whole stack.So a 10mm shim will reduce high speed and low speed compared to a 11mm.Your suggestion 3sounds good to me.i would consider using 4 24.1 initial comp shims and leave the 12.15 crossover
 
Joined
Dec 9, 2000
Messages
129
Likes
0
#3
Servus Marcus,

How is the CR doing ;-)

Do you ned the base plate shim on the RFS
I don't think you actually need it, but it obviously has a positive effect on the valving. If you'd remove the base plate, the seating area on the valvebody itself has a diameter somewhere between 12 and 16mm (I measured it, but forgot how much exactly). When I raised the overall height of the stack by inserting the 10x0.3 the influence of the base plate was seriously effected - and as it showed was not to my liking.

Dont forget the last shim sets up the shim stack strength for the whole stack.So a 10mm shim will reduce high speed and low speed compared to a 11mm.
I'm aware of that. It would be interesting to know if adding 1mm to the clamping shim would be the same as adding 1mm to the OD of all the shims - anybody?

Michael
 

marcusgunby

Lifetime Sponsor
Joined
Jan 9, 2000
Messages
6,450
Likes
2
#4
The Cr is going well the front forks are the best ive ridden ive changed the oil only and put 1 click on comp.The rear we are testing a Jer kit and its going well so far.The engine needs more development than the KTM but we are making good progress.BTW the CR steering is something else-seems fairly stable too.
 
Joined
May 17, 2000
Messages
137
Likes
0
#5
drehwurm,

This is a good question, what is the more significant factor, the clamping shim diameter or the thickness (gap) at the base plate?

Your stack #3 won't give us a complete answer unfortunately. Seems hard to imagine that going from 10mm to 11mm on the clamping shim would be so noticeable. It does have an affect on the whole stack though.

Stack #3 looks to be a good middle choice either way.

BTW-Nicely detailed posting.

James
 
Joined
Apr 25, 2000
Messages
20
Likes
0
#6
Hmmm --- This is interesting...

Notice how Jer doesn't comment in threads where your discussing shim stacks... Seems he would be able to help if he was interested in doing so...

How about it Jer -- why don't you jump in a help this young man with his stack....
 
Joined
Dec 9, 2000
Messages
129
Likes
0
#7
Servus James,

This is a good question, what is the more significant factor, the clamping shim diameter or the thickness (gap) at the base plate?
Thats an easy one! Just see it as a crossover shim like between LSC and HSC. And where is the answer now? Right there is none. If the gap is so big that the shims never hit the next stage, it doesn't matter if you make it even bigger. On the other hand, if you make it too small you actually go from a two to a one stage stack! IMHO this is like the apples and oranges thing ;-)

I'd consider the question if adding 1mm to the clamping shim diameter is equal to adding 1mm to all the shims above?

Michael
 
Joined
Dec 9, 2000
Messages
129
Likes
0
#8
Servus PT564,

Seems he would be able to help if he was interested in doing so...
I think you are a little unfair against Jeremy. First it is his business and nobody should ask for his knowledge for free. Second this is not a 'finding THE one and only great shim stack thing', because it doesn't exist. Third, I think Jeremys advice couldn't compensate for the info which is gained through learning here. And finally fourth, I'd say that if we go in the absoulutely wrong direction somebody would step in and point that out.

Michael, on a quest again :-)



[This message has been edited by drehwurm (edited 02-19-2001).]
 
Joined
Apr 25, 2000
Messages
20
Likes
0
#9
But isn't the objective of a moderator to "guide and teach"? If so Jer could simply state some guide lines for what this gent is tring to accomplish.... Simple -- doesn't bit into his bottom line one bit (and will actually have the inverse affect)..

Just my 2 cents...
 

JTT

Subscriber
Joined
Aug 25, 2000
Messages
1,407
Likes
0
#10
Rest assured PT564, Jer is surely following this thread. drehwurm is right that Jer telling him how to do it, will accomplish little in teaching him about how things work. Letting him (and us) figure it out on our own is the best way to true understanding. And,I too, am sure he will step in if the topic gets too far off track. He is already WAY ahead of most suspension guys, who won't give out the information to their "associates" (franchisees), that Jer provides to all at DRN.

I, personally,am enjoying this thread, thanks drehwurm! Keeps the "gray matter" firing.

------------------
JTT
Logic Over Hype Coalition
 
Joined
Apr 25, 2000
Messages
20
Likes
0
#11
I agree this is a GREAT thread!

Infact, this is what we should see more of on this board. It will give us all a chance to learn more about the different affects of taking away and adding different shims to a stack...

Thus, shim on.......and on....

BTW: I recently rode a bike with a great rear suspension. And, the compression stack was like nothing I've ever sceen before. It was made up of shims all with the same diameter! There was cross over in the stack, but other then that it was all 38mm OD shims (square shaped stack if you will)! The thing rocked.
 
Joined
Jan 22, 2000
Messages
14
Likes
0
#12
Yeah..great thread. I've been following this closely too. I've got most of it highlighted and written in a notebook. I really want to learn this stuff and this is about the only place that discusses it. I love this forum.

------------------

Vester
96 RM250
"Let's see if an "A" rider tries it first.."
 
Joined
Dec 9, 2000
Messages
129
Likes
0
#13
Servus,

Great that everybody likes this thread!

Still I'd like to get some input on the 'shim mechanics' like clamping shim dia vs. thickness vs. ... - nobody?

BTW stack #3 is waiting in the garage to be tested, but it seems like winter is giving his comeback here in Austria. Do I need a different valving if I put a ski on the front?

Michael
 
Joined
Jan 22, 2000
Messages
14
Likes
0
#14
I found some stuff on Eric Gorr's site last night that has me puzzled. This is a quote from his article on suspension tuning.

"With regards to the sizes of the shims, the larger the diameter and the thinner the thickness, the more easily the shim will bend and increase oil flow through the piston. The faster the oil flow the less the damping."

Which this leaves me confused now. Like on your #3 stack when you opted to change the 12x0.15 shim for the 14x0.15 for more LSC, you in turn lightened the damping because of the larger shim diameter. Same goes for the 19x0.1 shim that was switched for the 18x0.1 for less LSC. Because of the thicker diameter you in turn stiffened it?

Could someone clear this up for me?



------------------

Vester
96 RM250
"Let's see if an "A" rider tries it first.."
 

marcusgunby

Lifetime Sponsor
Joined
Jan 9, 2000
Messages
6,450
Likes
2
#15
I think i get what you are asking.The normal shims(ie the ones that sit against the piston or comp adjuster)are the ones the get less damping effect when they are made lager/thinner.The crossover/bendover shim does the opposite as the 1st stack(against the piston)bends over it so a larger bendover shim causes the stack above it to become stiffer.It takes a while to get your head around it.Its easier if you have a stack in front of you.