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  1. #1
    namagomi
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    Rockshox All-travel spacer and Blackbox/MoCo

    The answer is probably yes, but should the oil volumes be redone for the both air spring and dampening sides when a travel spacer is put in or removed? Can't see an answer in the service manual.

  2. #2
    Biking Like Crazy!
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    Good question there electrik! I just reduced my '11Totem Solo Air down from 180mm to 160mm to see how it would work on my Titus SuperMoto.
    It feels okay in the garage, though I have taken it out due to weather yet. My answer would be to leave the oil as is until it blows up.

  3. #3
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    Or you could play it on the safe (and less expensive) side and make sure of the oil levels. I'll assume the above was tongue in cheek.
    Rimmer - "There's an old human saying - if you talk garbage, expect pain"

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    Quote Originally Posted by electrik View Post
    The answer is probably yes, but should the oil volumes be redone for the both air spring and dampening sides when a travel spacer is put in or removed? Can't see an answer in the service manual.
    No. Oil volumes remain the same even though you may change travel with the spacers. That's why the manual does not specify different oil volumes.

    But, when putting in or removing spacers you will have lost oil. Oil levels are not set by height on the RS forks, so you should dump all the old oil and refill by the volumes specified in the manual.

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    Quote Originally Posted by TigWorld View Post
    No.
    ^ This.

  6. #6
    namagomi
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    Quote Originally Posted by AlexRandall View Post
    Or you could play it on the safe (and less expensive) side and make sure of the oil levels. I'll assume the above was tongue in cheek.
    Hah... Maybe a good idea just to be safe. Since the fork is almost new i was planning to try and capture any oil that came out and simply pour it back in. However...

    Quote Originally Posted by TigWorld View Post
    No. Oil volumes remain the same even though you may change travel with the spacers. That's why the manual does not specify different oil volumes.

    But, when putting in or removing spacers you will have lost oil. Oil levels are not set by height on the RS forks, so you should dump all the old oil and refill by the volumes specified in the manual.
    Quote Originally Posted by bad mechanic View Post
    ^ This.
    Ok.

    So for RS does the level of oil go by the stanchion length then? I was thinking that if I changed the spacer(and thus the travel) I would have to adjust the oil volumes to get the proper travel/spring rate and that the change in the length of stroke would mean that I would have to also adjust the volume of oil in the damper. Though I am unsure if the structure of the damper is dependent on the stroke or a different factor? Does it work more like the preload on a coil spring?

    Probably got about 3 different terms mixed up there, sorry!

  7. #7
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    The fork moves when used... It doesnt move or displace any more when lowered. The fork oil volume, at full length, is designed to allow the fork its full travel (to the bump stop). Think of lowering the fork as being in a continued state of mid stroke or something.

    Oil level is determined by the length of the uppers, not their position in the lowers.

  8. #8
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    Quote Originally Posted by electrik View Post
    So for RS does the level of oil go by the stanchion length then? I was thinking that if I changed the spacer(and thus the travel) I would have to adjust the oil volumes to get the proper travel/spring rate and that the change in the length of stroke would mean that I would have to also adjust the volume of oil in the damper. Though I am unsure if the structure of the damper is dependent on the stroke or a different factor? Does it work more like the preload on a coil spring?
    Your damper is not a spring, and your spring isn't a damper. They are independent of each other, and you need to separate them your mind.

  9. #9
    namagomi
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    Quote Originally Posted by bad mechanic View Post
    Your damper is not a spring, and your spring isn't a damper. They are independent of each other, and you need to separate them your mind.
    Hm, don't know why I would of confused that. Particularly because they are on opposite sides of the fork!

    Quote Originally Posted by One Pivot View Post
    The fork moves when used... It doesnt move or displace any more when lowered. The fork oil volume, at full length, is designed to allow the fork its full travel (to the bump stop). Think of lowering the fork as being in a continued state of mid stroke or something.

    Oil level is determined by the length of the uppers, not their position in the lowers.
    Ok, thanks this is what I was mainly wondering. So oil volume relates primarily to the length of uppers, but I am confused about a fork not displacing any more when lowered...

    Say a fork is 100mm and you drop it to 80mm. So now it sits into the travel, but does the spring rate curve simple shift to the left or does the spring rate get correspondingly corrected/scaled down somehow?

    What I am getting at here is that as the fork compresses the oil in the damper side must be forced through the damper, but if the fork stroke is shorter the oil must travel faster through the damper(perhaps making it seem like you have a thicker oil in there). Would dropping the fork into it's travel result in a different dampening force. I.e. would dropping the fork result in a fork with a lot stiffer compression and less linear feel? Could that be overcome with a lighter oil?

  10. #10
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    Quote Originally Posted by electrik View Post
    What I am getting at here is that as the fork compresses the oil in the damper side must be forced through the damper, but if the fork stroke is shorter the oil must travel faster through the damper(perhaps making it seem like you have a thicker oil in there). Would dropping the fork into it's travel result in a different dampening force. I.e. would dropping the fork result in a fork with a lot stiffer compression and less linear feel? Could that be overcome with a lighter oil?
    Are you making the assumption the damper is still using it's full stroke even when you reduce the fork's travel?

    The travel doesn't affect how quickly oil flows through the damper.

  11. #11
    namagomi
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    Quote Originally Posted by bad mechanic View Post
    Are you making the assumption the damper is still using it's full stroke even when you reduce the fork's travel?

    The travel doesn't affect how quickly oil flows through the damper.
    My idea of how the damper worked is the oil sat below it ready to flow through. I suppose it is also possible that when the fork sits into it travel, such as when you install a spacer, some of the oil on the damper side has already moved through the damper? In which case the flow rate of that oil would be the same as unreduced.

  12. #12
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    Quote Originally Posted by electrik View Post
    My idea of how the damper worked is the oil sat below it ready to flow through. I suppose it is also possible that when the fork sits into it travel, such as when you install a spacer, some of the oil on the damper side has already moved through the damper? In which case the flow rate of that oil would be the same as unreduced.
    No on this. If the oil was below the damper piston you would get a terrible
    oil/air cavitation problem. The damper piston is always in the oil a certain amount.
    That being said I wonder if the oil level in the damper side could be too full with the travel reduced and
    cause a loss of travel such as the oil migrating problems the Fox forks had?
    Maybe some oil needs to be removed there so the damper is submerged the same amount as before the travel reduction?
    Anybody?

  13. #13
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    The damper doesnt know where it is in the travel. Its not position sensitive. Its completely dependent on how fast the fork is compressing.

    The flow rate of the oil is related to shaft speed only. How much has or hasnt already passed the piston doesnt matter.

    Im trying to visualize the pressure difference with a DA spring when lowered... but honestly, thats the beauty of DA.. You can retune the pressures to do whatever you want it to.

  14. #14
    namagomi
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    Quote Originally Posted by blcman View Post
    No on this. If the oil was below the damper piston you would get a terrible
    oil/air cavitation problem. The damper piston is always in the oil a certain amount.
    That being said I wonder if the oil level in the damper side could be too full with the travel reduced and
    cause a loss of travel such as the oil migrating problems the Fox forks had?
    Maybe some oil needs to be removed there so the damper is submerged the same amount as before the travel reduction?
    Anybody?
    That was my original thought(too full), but apparently it should be fine as the length of the upper will remain the same. I don't know much about the oil migration problem with the fox though.

    Quote Originally Posted by One Pivot View Post
    The damper doesnt know where it is in the travel. Its not position sensitive. Its completely dependent on how fast the fork is compressing.

    The flow rate of the oil is related to shaft speed only. How much has or hasnt already passed the piston doesnt matter.

    Im trying to visualize the pressure difference with a DA spring when lowered... but honestly, thats the beauty of DA.. You can retune the pressures to do whatever you want it to.
    Ah, ok. So the damper is "dumb" to the position of the travel. Yes with the dual air I think your suspicion is correct that the negative spring can be increased to lower the spring rate when you reduce the fork's travel. Excellent.

  15. #15
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    The final compressed volume (full travel) is going to be the same.. so with a shorter spring, you're compressing less volume. You might have to bump up the positive pressure a bit to maintain similar bottom out characteristics. Play with negative pressure until its sensitive enough. Too much neg and you'll bottom out harder.

  16. #16
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    You generally need to add air when you reduce travel, since you're now supporting the same weight with less travel.


    Quote Originally Posted by blcman View Post
    That being said I wonder if the oil level in the damper side could be too full with the travel reduced and cause a loss of travel such as the oil migrating problems the Fox forks had? Maybe some oil needs to be removed there so the damper is submerged the same amount as before the travel reduction? Anybody?
    Fox doesn't have issues with the oil migrating in the damper. They have issues with oil migrating into the air chamber.

    No, oil does not need to be removed. The volume of the damper stays the same.

  17. #17
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    Quote Originally Posted by bad mechanic View Post
    You generally need to add air when you reduce travel, since you're now supporting the same weight with less travel.



    Fox doesn't have issues with the oil migrating in the damper. They have issues with oil migrating into the air chamber.

    No, oil does not need to be removed. The volume of the damper stays the same.
    Makes sense now. I just need to get an allen wrench so I can remove
    the blue knob on my Totem so I can visualize this!

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