Can someone explain fork oil? Confused on what to run, especially for sand....

Discussion in 'Thumpers' started by caffeine, Jan 12, 2007.

  1. caffeine

    caffeine Been here awhile

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    ...first i have people telling me 15w in my KLR with the progressive springs...then people saying use ATF which i guess is 7.5 w?

    what would be better for sand? what would help it from bottoming out?

    I ready to say screw it and just go with 10w or ATF as thats what I can find closest to me without ordering...just curious how each is going to affect the ride and what would be better for sand.
    #1
  2. Krabill

    Krabill Long timer

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    A YZ250 would be better for sand :lol3

    I've got progressives in my forks. Tried 10wt first - nice on pavement, too soft in the woods. Have 20wt in it now - a little harsh on pavement, but great off-road. I'd suggest trying to find some 15wt to start with if I were you. Not all the shops around here had it, but I did find it after stopping a couple places.
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  3. Max Kool

    Max Kool Xtankteam™

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    If it is harsh on the pavement, it would be even harsher in the woods, wouldn't it?
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  4. Krabill

    Krabill Long timer

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    No. It soaks up the bigger bumps without bottoming out in the woods. Gives a much more "planted" feel.
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  5. Monkey_Boy

    Monkey_Boy Los bichos atacan

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    Dont' confuse harsh with stiff. Harshness is caused by the spring(s). Stiffness is related to the damping system.

    Increasing the oil weight increase damping in both directions and will provide more stiffness (or resistance to movement) in the suspension. You will feel the stiffer compression damping affect through the handle bars. It's tough to find a good compromise with non-adjustable forks. General rule of thumb is to use as no more compression and rebound damping that is required for the conditions. You're looking for the right balance of compliance.

    Temperature, of course, affects damping as well.

    edit: Running thinner oil in the winter makes sense, heavier when the temps go up. Not sure what the stock oil weight is, but if it's 5 or 7.5, try 10w and see how it works. If it works, consider running 15w in the summer. You can't hurt anything by experimenting.
    #5
  6. caffeine

    caffeine Been here awhile

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    would you want stiffer or not stiffer in the sand?
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  7. Monkey_Boy

    Monkey_Boy Los bichos atacan

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    I'm going to guess that you want less stiffness = more compliance. You want the tires ride on top and not push into the sand.

    I think. :lol3

    Sorry, I'm not a sand rider but will be after this weekend's Jimmy Lewis school. :D I'll have a better answer on Monday.
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  8. Jack90210

    Jack90210 quia ego nominor leo

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    I have been running 15w with the Progressive spring mod, but am going to use 10w when I put the emulators in next week (waiting for bushings and seals to arrive). I recently bumped up a KLR suspension thread, gimme a minute to see if I can find it. EDIT: Here is the post/thread.
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  9. Zerodog

    Zerodog Long timer

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    What fork oil do you have now? Can you adjust anything on a KLR fork externally? One thing overlooked is oil height. You can raise you oil level to make your fork more progressive and more resistant to bottoming. A lot of guys like ATF in MX bikes. But if you are running 5wt now it is barely a change. But if you are running 10wt now it will make your fork worse. Another thing you can do is make sure your fork legs are flush to the top of your clamps. If they are up at all you are running a steeper head angle and it will make it worse in the sand. Other than that low tire pressure and staying on the gas is key.
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  10. caffeine

    caffeine Been here awhile

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    im running whatever is stock now...blew a seal and looked at this as an opportunity to put in progressive springs...just curious what weight fluid would be best...i think stock is 10, and im used to it in the sand now, just wanted to see if i should change it or just stick with it..i think ill just stick with it its not hard to change.
    -Rob
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  11. Rad

    Rad Done riding

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    Yes, yur gonna know sand by the end of yur class with J-L and yur gonna know this "road" all too well:lol3

    [​IMG]
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  12. tedder

    tedder irregular

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    Can anyone point to a good primer on the variables and why you might want to tune them? I.e., high/low speed compression, rebound, linear/progressive, oil viscosity and volume? I know I'm asking a lot. But I'm looking for a basic primer that is aimed at practical uses, not a 200-page engineering or racing text.
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  13. caffeine

    caffeine Been here awhile

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    what he said.....

    id settle for an explaination on whats better for deep sand, whats better for street, jumping, whoops, rocks, MX etc.
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  14. Jack90210

    Jack90210 quia ego nominor leo

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  15. caffeine

    caffeine Been here awhile

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    good read, thanks.

    still unclear though, on how things are going to handle in the sand...first impression is that id want a lighter oil, to have less damping, however, my first tap on the brake or let off the throttle, i can picture the bike diving? so im thinking that a stiffer, maybe 15w oil would be better?

    :ear
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  16. Krabill

    Krabill Long timer

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    Let me just +1 to what that Krabill guy said cuz he's really fuckin' smart. Yes . . . go with 15wt to start with and see how it feels. Fork oil is easy enough to change ;)
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  17. Monkey_Boy

    Monkey_Boy Los bichos atacan

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    Sweet! :lol3 Gonna be chillly this weekend. A butt-cold snow storm came through yesterday and we'll have a high of 40 or so in Primm today. That's warmer than in my town of Kingman, where it's 16 this morning. Brrrr.
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  18. 'Flagger

    'Flagger ..this space for rent..

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    Doesn't giving a '+1' to your own post risk tearing a hole in the universe....... or something? ::dunno
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  19. caffeine

    caffeine Been here awhile

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    haha i picked up 15w, I'll give it a try....
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  20. Zerodog

    Zerodog Long timer

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    I am not a klr guy but I do know a thing or 2 about how suspension works.
    I downloaded this for your viewing pleasure from the Kawi website.
    http://www.kawasaki.com/Scripts/ImgServ.exe/convert?ilFN=E%3A%5CEpcimages%5CI12%5CI1289%5CF2340.TIF&ilSC=35&ilIV=0&ilBR=0&ilIF=P&ilRE=8
    This is a pretty simple fork. It looks like there are no external adjustments to this puppy besides air pressure. The damping is controlled with item #44022 moving in and out of #44013. There are no shims or pistons. Oil rams through holes to control the damping effect.

    So the tunable items are:
    1. Fork springs
    2. Oil viscosity
    3. Oil height
    4. Air pressure
    Stiffer springs will make the bike ride higher in the stroke. Good for sand. Progressive springs will give a softer initial ride but resist bottoming.
    Thicker oil will slow down the damping. This is good for sand as well. 15wt is probably a good way to go if stock is 10wt.
    Oil height will control bottoming resistance as well. The higher it is the harder it will be to bottom. The air chamber in the fork acts as a spring. The smaller the volume of air the faster it will ramp up pressure under compression.
    I am not 100% is this item #16126 is on all KLRs but from the diagram here it shows an air fitting. This is a really good adjustment to make.
    You can add air pressure to the fork through the shrader valve on the fork cap. This will also act as a progressive spring. The more pressure the harder the will be through the entire stroke. You can then tune with a small bike pump the way your fork rides. Less pressure it will be softer and much better in the rocks. More pressure the higher in the stroke the fork will ride and also be much harder to bottomout. You can pretty much adjust your springs on the fly with this. Before you dump cash on any springs.......unless you are really heavy enough to need them. I would fully test out the air pressure adjustment of this fork.


    For sand on MX bikes you run slow damping all around. Slower compression to aid low speed damping for big G outs and large sand whoops and slower rebound for these same items. You want the front to ride higher. This angle helps with the bikes geometry. The higher it rides the slacker the head angle. This makes the bike more stable and handle a little slower.
    Tips for riding sand are this:
    1. Go faster than you think you should
    2. Never touch your brakes
    3. Roll off the gas slowly. This is your brakes
    4. When turning give it even more gas after you get into a turn.
    5. Lean back.
    6. Stand while going straight and sit in turns.
    7. Go fast
    8. Stay on the gas
    9. If you don't crash while riding sand you are not trying hard enough
    Big bikes suck in the sand. They are a lot more of a handful than a small bike and harder to learn on. Once you get the hang of it though it isn't too bad and can be a lot of fun. Good luck. Have fun!

    [​IMG]
    #20