shim shuffle final - KTM WP forks Part 3

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#1
Servus,

Now this is the last part (well, at least for some time ;-) of my 'backyard tuner' experiments. I learned a lot and was lucky to get some positive results. Nevertheless I'd do it again any time.

Again, I can only emphasize that the following works well for me, but very likely will not work for somebody else. I'm posting this to give interessted people a starting point for their experiments, but I do not intend to give anybody advice on how to setup their shim stacks!!!

My aim was to improve fork action on bottoming, deflecting and headshake and I think I finally (but somewhat unexpectedly) suceeded in all three parts with the addition of getting even way more adjustability on the forks. The addition of an Öhlins PDS shock and Scotts steering damper helped somewhat with the original problems, but I'm of the oppinion that the forks are the main culprit!

I would describe my result as a GNCC setup - a little soft but ok for MX and very firm for east coast type enduro, but great on anything fast with this extra safety margin for unexpected stuff. I've been racing this setup and I've been trailriding in Greece for a week with the same setup and never felt uncomfortable. For the moment I'm really satisfied ;)

Next thing will be some experimenting with the shock spring, soft spring more preload and maybe a setup for the forks from MX-Tech just for comparison - if time and money permits it!

If you haven't followed the first two parts of this experiment you can find them here

http://dirtrider.net/forums3/showthread.php?s=&threadid=5410
http://dirtrider.net/forums3/showthread.php?s=&threadid=11225

Info about the later referred updated WP parts is found under

http://dirtrider.net/ubb2/Forum28/HTML/001641.html


For setup: I'm 80kg (176lb) with gear and use the stock 0.42 springs with Öhlins 5wt fork oil, oil level 150mm.

What I did:

1) Base Valve

After having installed the new compression tap and needle with the 3mm orifices LSC was too soft, so the logical conclusion was to increase LSC even more and leave the last HSC stack untouched:

24x0.1 5x
12x0.15 crossover
22x0.1
21x0.1
19x0.1
17x0.1
14x0.1
13x0.1
12x0.1
11x0.25 clamping shim
18x0.3 base plate

18 out on the comp clicker provides a plush ride with some headshake on the fast parts - 10 out on comp is PERFECT for racing. Firm but supple, no headshake, no bottoming - I like it. The deflecting had been sorted out before with the little increase in HSC => replaced 20,18,16 shim with 21,19,17 !!! Alternatively (because 17,19,21 are not available from KTM or WP) replacing the 18x0.1 shim with a 20x0.1 would probably work also.

Highlights (most noticeable positive changes) in my experiments where the step from a 10x0.3 shim to a 11x0.25 and opening the gap (increasing HSC) from 16x0.1 to 17x0.1.

IF making some more changes (which I probably won't do), I'd add another 24x0.1 shim on the LSc part and remove the 13x0.1 from HSC - just to see the difference in LSC and HSC!

2) Mid Valve

I installed a stiffer spring (from the update kit) and left the valving untouched - no noticable effects.

3) Rebound

Together with the new tap and needle I changed to the KTM SXS spec rebound stack, but I don't dare to make any statements on the effects. All I can say is that I went from 12 to 18 clicks out and that otherwise is seems to work fine. If I'd be under pressure to make an assumption, I'd say that this helped on the headshake problem, but I've no proof for such a statement.


Comments are welcome!

Michael
 
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#2
Servus,

Either I'm getting faster or just heavier, but I'm still too soft on LSC. Nevertheless to make nails with heads (as we say over here) I e-mailed Jermey and he was happy ;) to work his magic on my forks. So today I sent my base valves and rods to him to see what MX-Tech is capable of. If it weren't for my curiosty the expenses (express shipping from europe and customs/taxes) would never justify this - the expenses are way higher than the costs of revalving, but I NEED TO KNOW!

Michael
 
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#4
and the saga continues ...

Servus,

Ready for some sleuthing :p

Since my last posting I've been busy working on the MX-Tech setup which, as you might already guess, didn't work as expected. Take a look at video #1

http://members.eunet.at/mpetkov/MX-Tech/MXTech_as_delivered.mpg

and closely watch the front wheel reaction when hitting a bump. The MX-Tech valving worked great on low and mid speed stuff (actually so good that I decided to keep working on it instead of going back to my setup) but I had severe problems at higher speeds. Jer was very helpful as always, but if I learned something it was to only have BOTH, fork and shock, reworked at the same time. If, like in my case the Öhlins shock, there is an unknown variable even guys like Jer have a hard time to figure out the right setup.

Anyway, I don't want to tell the whole story yet so take a look at video #2

http://members.eunet.at/mpetkov/MX-Tech/MXTech_latest.mpg

to see how far I've come (this video has been made two month later and conditions were even worse) . For comparison watch a 2001 Yamaha 426 on the same part of the track:

http://members.eunet.at/mpetkov/MX-Tech/Yamaha426.mpg

Okay guys, tell me what you think the problem is in the first video and what you think I did to improve it! Get ready for some surprises :p

BTW, while the shock had some influence only clickers where changed between video #1 and #2.


Michael
 

MACE

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#5
(yeah, like I have a clue...)

Is it rebounding too quickly? Either that or did you open up the valve orifice? Don't the WPs have larger cartridge rods and therefore push more fluid through the base valve.

You know it would be a very useful product if someone filmed a suspension tuning guide that showed problems and solutions (maybe to accompany a book).
 
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#6
Michael:

You're getting closer to the stack that I mentioned many months ago :)

I think doubling up the cross over shim would give those high speed hits a little more movement before the high speed shims come into play. Adding more low speed shims (24mm) will keep it from diving too much and you get the best of both worlds.

If you ever get to playing with it again, give the double cross over shims a try.

What were the results of Jeremy's set up vs. your's? Are you still riding Jeremy's mods or did you go back to your set up?

Cheers,
 
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#7
Michael:

After watching the videos again a few times, I would also say that you have too much preload on the back, or your spring is too stiff. Your bike is riding way too far up in the travel on both ends. The first video your rear suspension only uses about 1/3 of the travel. Watch the YZ again and see how different your ride hight appears.

Increase the sag in the back, go slower on the front rebound and faster in the rear. You'll hook up better, dance around up front less and feel like you're actually in control.

Watch some video of Shane Watt's or RC. Their rear wheel hits the fender on just about every thing they go over. That nutcase RC is running like 125mm of sag in the rear, with telephone poles for forks. Go figure, but it seems to be working. You're going fast enough for it to be comparable in video form anyway :)
 
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#8
Only a Guess...

Looks like more compression in the rear in the second video to keep from getting as deep in the stroke. Maybe less rebound there too. The forks look like they are riding high, but then maybe that's due to accelerating. It may also be from the mid to high speed compression damping. The imbalance was apparent when the bike was bucking in the first video. Looks much better in the second video.

The Yamaha looks like it is using more fork travel and maybe giving a softer front end performance. I wouldn't say it was better without riding it and looking for arm pump and feeling the steering precision. It would have been nicer to have been standing, a little hard to compare that video.

Nice videos Michael, good for discussions.

James

DON'T KEEP US IN SUSPENSE TOO LONG!! WHATS THE RESULTS?? :confused: :eek: :scream: :silly: :p
 
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#9
Servus,

Thanks guys for joining me again!

MACE:

Yes, my first thoughts were also that the low flow MX-Tech pistons in connection with the larger WP rods were responsible for the 'locking up' of the forks. They are not though! Those low flow pistons give a very controlled feel I start to like more and more. Also even though on the video the forks look really harsh, the ride didn't feel like that - I was really surprised when I saw it they first time.

BTW KTM included a video with the 1999 or 2000 models which had a suspension tuning guide, but it wasn't very helpfull. Someone still have it?


c3hammer:

At first I would have said that the MX-Tech setup was better on low to mid speed stuff while my setup clearly worked better on the high speed stuff. Now I'm really getting satisfied with the MX-Tech pistons and mods - they are nowhere as plush as the stock setup though, but I guess you just can't have anything.

Yes, I have lots of preload on the shock, but I use a soft spring. This combo makes for great turning and eliminates the 'kick back' the PDS is so famous for. Also the whole bike is setup now with soft springs/much preload because I've found this to just work best for me. Watch the second video closely and you'll see the shock bottoming and going sideways on a bump. Right now I'm running the clickers on the shock too far in to compensate for a weak low mid compression and rebound valving on the shock - this is going to get fixed soon. Again, the shock has not been the real problem!

Oh, and thanks for comparing me to that nutcase :cool:


James:

Hmmm, not bad. Yes the shock has more compression to equal the forks, but also more rebound. I'm also of the oppinion that the forks only look to ride high because of the acceleration - this is a 520 at full thrust, not some tiddler.

I was also amazed at how much travel the Yamaha is using, but when I stayed behind this guy for some time his back wheel often looked out of controll. I think the bike is setup too soft for his riding!

Ok, some of those bumps are sharp edged some are not so the speed range is in mid to high speed regions. Jer is not only known for his low flow pistons, but also of being a 'lots of mid valve' fan. Need I have to say more?


Michael
 
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#10
Thanks for the critique. Are your forks using full travel on other parts of the track?

Does thank Yamaha rider know his bike and riding style is being scrutinized on the internet? ;)
 
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#11
Servus James,

Are your forks using full travel on other parts of the track?
Yes, I have some more videos but my web space is too small for all of them. Also, like it is said in the books, I'm bottoming over one or two other parts of the track.

Well, I told the Yamaha rider that he can watch the video on the net, but I forgot the part about 'the whole world can also' :p

Michael
 
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#12
Servus,

Well, if there are no more takers here is the magic word: MIDVALVE FLOAT!

First thing Jeremy recommended was reducing the midvalve stack and while this helped somewhat there also were negative side effects. Much of the 'nice' low speed control was lost without getting completely rid of the high speed probs. We tried somemore stuff like stiffer springs and even less midvalve, but to no avail. I went on on my own and finally the breakthrough came when I went radical and tried even less midvalve combined with less midvalve float. This clearly was a step in the wrong direction so the guidelines were clear:

1) more midvalve float to get the midvalve working later and get some flow for high speed stuff

2) more midvalve damping to keep the controlled feel

3) more LSC on the basevalve to compensate for the later starting midvalve

4) get rid of the stiffer springs as they worked for MX but not for offroad - so I went with the stock springs but much more preload. This also allowed me to open the comp clickers a little more to gain some plushness on the small stuff.

and it WORKED as you can partially see on the video. Actually the fork action improved on about every aspect and got even more versatile too.

I wouldn't be me to be satisfied now so I'm going to try even stiffer midvalve settings combined with more float till things get worse. Fortunately revalving the midvalve on the WP forks is just a little more work than woring on the base valve - I can now do a complete midvalve revalve including removal, disassemby, assembly, installation of the forks and cleaning up the workplace within 1 1/2 hours. Did it often enough!

Any question?

Michael
 

marcusgunby

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#13
Its very inforamtive what you have done and very useful for others.I never would have thought to go the way you described.-Well done.How do you rate your set up now to the original/best set ups you have rode.BTW on my CR125 i have had my forks done by a local tuner and they increase midvalve float/decrease midvalve stiffness and decrease base valve stiffness(LSC and HSC) and use softer springs and lower oil heights.The only downside is they do blow through the stroke when the bike is really muddy.I never would have guessed they went so far on the valving by seat of the pant feel.
 
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#14
Michael,
How much float are you running and how much did you increase it? I also have been working on these forks for quite some time and had come to the conclusion that I needed to start messing with the midvalve after exhausting all other options. I had previously tried to increase the midvalve strength and decrease the lift, but it was defenitely a step in the wrong direction. My next step was to increase the lift on the midvalve (from stock) to see what effect that had on the performance of the fork. It's nice to see someone else going down the same "path" and discovering the same things :) !
 
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#15
Servus,

Marcus:

It is a no-brainer to say the current setup is easily the best I've had so far. What I like soo much on the MX-Tech setup is, that this 'blow through the stroke' feeling is completely gone. Before I was always a little cautious when I saw deep ditches or g-outs, but now I just aim for them and gas it :D

Yes, I've also become a convert to the soft spring/much preload side, but the downside you describe is true: on a muddy ride you are much closer to the edge than with stiffer springs. But then, on muddy enduros I'm in survial mode anyway and not going for some brave heroic riding.

As for the base valve, I actually increased LSC a little. That's because I had the feeling that I was lacking low speed control (for example on downhills) after increasing midvalve float, but had to use too stiff clicker settings to compensate for this. Increasing LSC on the base valve did exactely what I wanted without becoming to harsh like with the clickers. But Jeremys setup relies a lot on midvale damping so this was to be expected.

Bud-Man:

Right now I'm running 0.65mm of MV float which is considerably more than the MX-Tech setup, but way less than stock. I think stock is around 1.5mm which IMHO brings the MV into play very late - too late! I can't imagine increasing MV float from 1.5mm on an already soft setup did work, but I might have missunderstood something here. Did you measure your stock MV float and what setting are you at now?

Things are getting very complex here again. Jer gave me a base-setup I could start working with, finding good MV settings (float, valving) for the stock pistons is another chapter, but I agree with Bud-Man that this is probably the key to get those WP's working.


Michael