Fork midvalve question- and other DIY suspension tuning

Discussion in 'Dakar champion (950/990)' started by slackmeyer, Sep 5, 2011.

  1. bobone

    bobone Been here awhile

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    another one happy rider with your sertup. i softened it a bit because i ride more technical single trail than open desert but i'm really happy with it.

    now i just have to fix the shock... how did you guys set up yours?
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  2. uk_mouse

    uk_mouse Aquatic adventurer

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    Just wanted to say thanks for all this excellent information. I've got my forks in bits right now and I've just ordered a load of shims, plus new .62 springs from Konflict. I'll report back when it's all back together.

    I've noticed no one has done anything with the rebound stack on the base valve, which in the stock setup is just a single thick shim acting as a check valve, I think. Is there a specific reason for this? Can everything rebound related be achieved by altering just the mid valve? I'm mainly asking out of interest, not because I plan on messing with it, not at first, anyway!
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  3. 1coolbanana

    1coolbanana Long timer

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    I found this previous iteration little harsh for the riding I do so softened up the base valve a little.
    Would be great for hard charging :-) But Im old and soft now :lol3
    This is what I ended up with and for lightly loaded dirt touring this seems great, doesnt bottom out yet plush.
    This is not for hard going or single track but this works great for me.
    Just recently did 1000 km in a weekend on mostly poor condition dirt and corrugations and it was fantastic.

    No way I could have got to this level without all the help and info here :thumb
    Awesome resource :-)

    [​IMG]
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  4. Johnf3

    Johnf3 Long timer

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    All the rebound for this fork is controlled by the valve in tbe cartridge. The oil is pushed down by the mid valve and then through the base valve. That is all the base valve does.
  5. Torque

    Torque Been here awhile

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    Remember 9 times out of 10 harshness, if caused by valving, is created by the mid valve. Maybe a bit of a Xover in the mid may have directly addressed the harshness.
    Did the lightening up of the base valve help?
    The base valve flows about 1/3 the fluid mid valve flows.
    Almost forgot, most would increase float instead of xover. Forgot because I run zero float valving on all my work for years now.
  6. 1coolbanana

    1coolbanana Long timer

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    Hey @Torque
    Im just a trial and error hack.
    Couldnt have gotten anywhere without all the help here.
    My base valve change seems to have helped but maybe placebo.
    You seem to be a well respected suspension tuner.
    How about you chip in and show us what you would do with this stack to improve on what we have :thumb
    Cheers
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  7. uk_mouse

    uk_mouse Aquatic adventurer

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    I guess I phrased my question badly - I was just interested from a theoretical viewpoint why there's no rebound stack on the base valve, when there could be.
  8. Torque

    Torque Been here awhile

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    My tunes for some years do not relate to the old school stacks used by 99% of the tuners and would not be a viable comparison. Therefore.
    I will look through my records after I get a deadline prototype bike done and get back with you later with some stack info and hopefully more.
    My concern also may be the .60 springs.
    If you would please give me info to save me time from looking through threads.
    Weight, bike model year, travel, terrain, how hard your riding the bike. More the better. Do you stand when riding, carry bags more often than not. I will try tonight or tomorrow to relate some solid info.
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  9. Zuber

    Zuber Zoob Supporter

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    Oil is drawn through the base valves on rebound to refill the cylinder. The oil can easily cavitate with any restriction, so not good to use for 'much' damping.
    Also, rebound is always low speed damping and only has to counteract the spring. You don't need to modify it much if you don't change the spring.
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  10. 1coolbanana

    1coolbanana Long timer

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    @Torque

    220 lbs geared up
    2009 990 Adv
    250 mm travel
    Poor condition dirt roads.
    Mostly "dirt touring"
    Dont ride hard core anymore but still like to have fun.
    Stand when needed but Im getting lazier with age.
    Always travel light.
    Last iteration of valving above post.

    Cheers

    This is loaded for a week away

    [​IMG]
  11. Torque

    Torque Been here awhile

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    220lbs geared so about 200lbs without gear. Nice looking bike by the way.
    Seems you are looking for plush. The .60 springs are too light and will not be as smooth in the studder / washboard type of bumps. The springs are compressed too much prior to hitting a bump and that is the name of that game. You can leave them if that is your desire but know it is part of your issue.
    Pre-load at 14mm with the pre-load adjusters all out is a pretty good area to be in. If you were to go to a .66 or .68 for instance then I would reduce that to 8mm as you have 10mm of increase in the adjuster.
    You can shorten your spring by a couple coils to increase the rate and put a pvc or aluminum spacer in there if you are a hands on save money type of guy. I tend not to shorten springs unless customer is aware in advance. I just worry about putting heat to a spring although have never had an issue with one I have shortened or that others such as Race Tech has shortened.

    Oil height at 110mm.
    So the ktm / Husky's with the 4860 forks being the open bath and the Xplor are basically the same. With 300mm of travel at 110mm will have some bottoming resistance when the air in the fork compresses at the bottom of the stroke. That will start about mid stroke if you have a high oil level such as 100mm. Now when you have a fork that has 250mm of travel then you are not compressing as much air with a shorter stroke. So although it may seem you have to lower the oil level with a shorter fork for example to 120mm you in fact need to raise the oil level to maybe 90mm to get into the air spring.
    Example: Noah Kepple when on 500 ktm pro level offroad high speed we would run 100mm oil level at some venues. This is noticeable bottoming resistance to the point that 95mm would have been too much oil and would start to affect the rebound too much causing the fork come back too fast.
    On the 1090Rs with supposed 210mm, actual 200mm I run 90mm and cant really feel the air spring much if at all. On my 990 245mm running 100 and cant really feel the air spring there either. But that is 500lb bike.
    All that said if you are not bottoming I think you are in a good place at 110mm for optimum plushness.

    To the stacks
    I may not nail this out of the box but I have a good idea of what is needed. The if and your choice is the float. .5 to 1 or more if you want depending on how much damping you want and how early you want the damping to come into play.
    Your base valve is the system that will give you hold up in the stroke. Very similar to the high speed in your shock. Close the high speed in the shock and your shock will firm up considerably overall and actually can make the rear ride higher in the stroke. As mentioned earlier it is much much easier to dial in harshness with the mid valve than it is the base valve. So you really want to get a balance between the two that will work best for you. Remember the mid has way more oil flow than the base.
    If you are not getting air and just enjoying a pleasant non aggressive pace I would still tighten up your base valve and loosen up the mid valve.
    To hold the forks up I would likely do (3) or (4) 24x15s then taper down even number .10s all the way to 10 or 12 clamp or less to soften.
    Now what you did with your base valve in your post is what you should do with your mid valve. Two face shims and a cross over then another 24 diameter shim and taper her on down then choose your float. You can do more float no xover but I the whole reason I run no float systems is because I want control early and direct. Different topic.
    Example: Just did an updated revalve for Worcs race and after dial in compression was at 12 clicks. I went back into fork and stiffened up the high speed / after cross over so we could run 17 clicks out. Initial movement was more compliant / plush but still with enough damping to slow her down in high speed hit. Win Win as they say.

    I even use a cross over after one or two delta shims in the rebound. I want the wheel back on the ground. I may go heavier valving after the cross over to keep it real but initial movement I want the wheel back on the ground.
    I wish I could be more detailed but my stacks are way heavier than these and I design adjustable blow off valves, so wholesale different designs.
    I always make a strong effort to post absolutely accurate info. If I make errors please let me know as I will correct. Too much bad info out there. Any questions feel free and I will post as time allows. I hope this was helpful.
  12. 1coolbanana

    1coolbanana Long timer

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    Thanks so much for the detailed reply. :thumb
    To be honest, the reason I did what I did with the base valve was because, 1) I dont really know what Im doing and 2) I was lazy and didnt want to disassemble the forks for a 5th time :lol3
    Armed with your info above I may revert the base valves and make some changes as you suggest.
    Thanks heaps, appreciated by all Im sure :beer
  13. bobone

    bobone Been here awhile

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    so... after some quite extensive testing i vame to the conclusion that i love my forks, but i hate my shock.

    i am 90kg, riding a pony so 210mm. atm i have 150 std springs. rear static sag 15mm, rider sag 50mm

    i cannot seem to get the rear wheel to bite the ground unless i sit on the passenger seat. my rear sag is 50mm with 0 preload. to me it feels too heavy spring, but i'm not really experienced, and something can be done on the stacks as well. the feeling of the bike is that the more i sit back, and the more luggage i carry, the better it is. it also kiks out of jumps, rocks, etc...

    my riding habitat is alpine, so no long desert stunts, almost no whoops, but rocks, big rocks, small rocks, mud, loose gravel, etc...
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  14. Torque

    Torque Been here awhile

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    The bike is a bit front heavy. Did you loosen the high speed 17mm adjuster at the top of your shock?
  15. uk_mouse

    uk_mouse Aquatic adventurer

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    I feel the same way as bobone about my bike, the front is excellent (since I revalved the forks using the "johnf3 formula") but the rear is too harsh. I'm on a 2004 S model so my spring is 140, and I've backed off the high speed adjuster all the way. The back end still skips and jumps over small rocks and whoops. I agree that putting more weight on the rear makes it handle better.
  16. 1coolbanana

    1coolbanana Long timer

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    Worth every penny

    [​IMG]
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  17. Torque

    Torque Been here awhile

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    Re-valve what you have, put a variable spring on it. Oem shock is a great shock and with this it will gobble up everything you throw at it.
  18. 1coolbanana

    1coolbanana Long timer

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    Agreed, its a good quality shock, if you can get someone good to do it.
    I can do forks but not shocks.

    After 3 attempts by "the best" hacks in the area and spending nearly $1000 to get rubbish results, I bit the bullet and just replaced it with a custom order shock.
    Was worth it for me it in the end.
    Torque likes this.
  19. skuikka

    skuikka Been here awhile

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    The rear should sag about 1/3 of the travel with the rider on. If that can't be reached even with zero preload, you need a softer spring. I have a Adv shock in a SE, 255mm travel, 140N/mm spring and a 100kg rider. This is in the ballpark. The grip with the stock valving is unbelievable compared to stock SE shock. It's plush but takes jumps and hits reasonably well. But the spring has to be right to start any adjustments with any shock. You can patch some bad springing with the damping but it is a "fix"
  20. Zuber

    Zuber Zoob Supporter

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    The shock on these bikes is really a compromise to allow two-up riding. So, it is reasonable that you need a softer spring to optimize it for solo.