Fork subtanks... are they for you?

Discussion in 'Thumpers' started by creeper, Aug 27, 2006.

  1. meat popsicle

    meat popsicle Ignostic

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    Bill,

    just in case you did not catch my joke, a "sock monkey" in an online discussion forum is slang for someone's extra "profile", so they can post things anon. :D I think it is a funny term. And thanks for your contribution to suspension threads recently. That KTMTalk thread was a very nice find :nod

    Also, just in case you didn't follow Zerodog, or didn't peek at the link I posted on the previous page, you need to be careful when changing these specifications. Raising the oil level will indeed firm up the fork, by trading oil spring for air spring, but you will increase the fluid pressure inside the fork, and run the risk of hydraulic lock. Who's to say when that will happen :dunno but I don't like the sound of it (probably damages the valves). Or if that doesn't happen you might just blow your fork seals out. I think that would ruin anyone's day.
    #81
  2. bmwktmbill

    bmwktmbill Traveler

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    Meat,
    You got me on with the sock monkey comment, I thought it was a new form of ritual self abuse practiced with new friends after an evening of suspension tuning.

    I have a question.
    Are you going to volunteer your ride for the stock suspension subtank upgrade?
    You would have to pull the fork caps to install the subtanks anyway, then you can add say 10mm of preload spacers and 25cc of fork oil per leg depending on your numbers. The oil that you add could help adjust your damping depending on the viscosity you use.

    You might end up with a very nice ride without changing springs. Preload spacers and fork oil is only pennys.
    I vote for you for test pilot.
    I would do it but my bike is already lowered.
    Unless your sag numbers are way off it might work??
    Bill in Tomahawk, WI.
    #82
  3. meat popsicle

    meat popsicle Ignostic

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    Thanks for the nomination, but I am taking Zerodog and creeper, and the rest of La Familia at their word: professional suspension tuning is the Number 1 upgrade that you can do for the LC4a.

    And adding the subtanks alone will only serve to soften your setup (hope I got that vaguely right :lol3). I won't play around with raising the oil level to compensate because I have no idea when that will create enough internal pressure to cause the hydraulic valves to fail, or simply blow out my fork seals.

    I will be doing spring upgrades (and perhaps valves depending upon the recommendations of the professionals) with the subtanks integrated into the rework when I have that extra C-note.
    #83
  4. bmwktmbill

    bmwktmbill Traveler

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    Meat,
    I understand where you are coming from. Just don't get yourself sprung too stiff. Check the numbers in the WP manuals. And trust yourself.

    We have ATV trails here and they are ideal for testing suspension in the real world. They are all the way from road racing on blacktop an good gravel to wide single track and back. We have plenty of mud, rock and sand thrown in too. Well it'd the stuff the glacier left behind.
    It's a mix of every sort of riding.

    I talked to Brad Lowe tonight(Lowe Racing). He is the suspension guy who did my revalve and lowering work. Suspension guys don't alway think too highly of sub tanks and it was his opinion that a good revalving job made sub tanks unnecessary.
    I didn't want to argue but he might not be a dual sport rider.
    Most suspension tuners are racers in one form or another.

    And isn't suspension work the best part of motorcycle tuning.
    Man, you've got to ride to do the testing.

    Bill in Tomahawk, WI.
    #84
  5. JamesC

    JamesC Adventurer

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    Forgive the slight diversion. I've enjoyed this thread very much and have learned a lot. Thank you.

    Can I ask for informed opinion on this application for a sport bike. It seems they have just recently shown up on a Marzocchi RAC 50mm superbike setup as follows

    [​IMG]



    I'm wonder if the adjustable valve type are in use here but more importantly just how they are really put into use. The rider of this bike is a champion many know so obviously knows his stuff and is testing but would this perhaps be used in place of a per-track spring change or perhaps to counter..I don't know, unexpected temperatures? Why would a top level superbike need something so seemingly macro? We're not talking about street-to-track nor street-to-dirt. Are there advantage my small brain can't come up with for a professional superbike calibre setup?

    Or maybe this is a gas charged reservoir on top instead of an Ohlins bottom mount?

    Thanks!
    #85
  6. Jan from Finland

    Jan from Finland Been here awhile

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    I would say that your latter asumption is right. Most likely it's a high pressure unit with hose connected external gas reservoir. So, in function it’s just like piggyback rear suspensions have been years. The fork contains high pressure nitrogen gas instead of air. The suspension fluid is kept under gas pressure and the gas-fluid separating piston is in that reservoir.

    The benefits of such a system according to Ohlins are: “The pressurised damping system improves the front fork function at high frequency movements. The immediate damping responses improve the tyre feeling and also give more possibilities for adjustments. Of course the combination of spring and air-gap (oil level*) still gives a possibility to adjust the characteristic of the fork to suit different tracks and riders.” and “The pressurisation prevents cavitation of the fluid and the shock absorbing action is therefore more even. The external reservoires also contribute to better cooling of the fluid, giving longer service life for both the fluid and components.”
    #86
  7. meat popsicle

    meat popsicle Ignostic

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    [​IMG]

    :bluduh

    I really don't think I am the fella to do this seal. Need a graphic designer.
    #87
  8. motometal

    motometal i like motorcycles

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    regarding the small tanks on the green bike, I don't see how those could work with a bladder etc. as suggested...the displacement of the forks is way greater than what you have with a rear shock...you would need a much larger tank with bladder for this to work. Actually they have made forks with a bladder inside the forks to separate oil and air, for mx bikes.

    ---

    With any sub tanks, I think it would be a useful experiment to fit a fast-acting pressure gage atop the forks, and the bottom of the tanks, with a "hold" feature to record max pressure. Then try this with the valves opened and closed. I can see how the sub-tanks would have an effect on g-out situations and circumstances where the forks are gradually compressing, but in the case of a large force on the forks suddenly being applied, suddenly, then going away (say, a hole or rock), I find it surprising that you could get enough air to travel through that little 1/8" hose to make a difference.

    it takes time for air to accelerate, then travel through that little orifice (the hose and fittings) to equalize pressure with the forks (which is only at it's peak for a very small fraction of a second)...then about the time the air starts really flowing through the hose, the situation reverses as the fork is rebounding.

    ever fill up one of those portable air tanks using your air compressor? Even with a 1/4" hose (as oppsed to the 1/8" hose on the sub-tanks), it takes quite a few seconds to get any kind of pressure in the portable tank, even when you have say, 100 psi in the main compressor tank. I could run over many bumps on my bike in that period of time...
    #88
  9. bmwktmbill

    bmwktmbill Traveler

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    Interesting to see this thread re-emerge.
    Since my above comments , I bought the Infinity Machine and Design subtanks, installed them and rode my LC4640a darned near around the world on the 45th parallel with a side trip to the Gobi desert in Mongolia.
    I rode with full travel gear and lived off the bike for 5 months.

    The only reason I say this is to give a frame of reference to my comments.

    In real world riding the tanks actually work.
    They are nice because they are simple and durable...and only two settings...on/off. Your tired of riding brain doesn't have to think very hard when your body really doesn't want to get thrown off the machine because road conditions have dramatically changed.

    Think of off road tracks, potholed gravel, 50 miles of road construction detours, 6 lane interstate, broken asphalt or tight turn mountain highways.
    You can get it all in one day.

    So when you are riding and conditions change it is easy to adjust the bike.

    Thise tanks are the easiest and most effective way to have two suspensions.
    They really works and it make the ride that much safer.

    Off road you can make the ride plush and on road firm things up
    I know the system works because of the many times I actually stopped riding to change the tanks
    .
    That says a lot when you are on the bike every day and just want to get some food and a place to rest.
    The built in fork bleeders are the icing on the cake.
    bill
    #89
  10. Zerodog

    Zerodog Long timer

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    I think you are thinking about it in reverse. The tanks help the most with the small bumps. If all you need is big hit performance a high oil height takes care of it. It is just at the cost of small bump compliance.

    It is the volume of air displaced not the speed of the air or the hit that makes subtanks so effective. Small bumps = less air to flow through the valve/ orifice. The small amount of air displaced equalizes quickly. The fork acts like it has a very low oil height. Big bumps = more air. The effect of the big hit is that the air can't flow through the valve fast enough. Pressure builds in the fork and it resists bottoming. It acts like it has a very high oil level.


    The tank on the race bike could just be a small subtank. They could be using it to control fork dive and bike geometry in a corner. On a long sustained push like a corner subtanks do let a fork dive more. On a road bike that could be awesome. Or they could just be a variation of a twin chamber fork with a bladder.
    #90
  11. meat popsicle

    meat popsicle Ignostic

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    Zerodog,

    I noticed on your website an explanation for this, I assume prompted by people asking why your kits don't utilize the stock bleed screw hole. From your explanation it seems that you addressed the issue of adequate flow between the forks and subtanks during R&D. During that process if 1/8" were truly inadequate you could have opted for 1/4" easily, but after reading your reply above it seems you are saying the size of the connection between the forks and subtanks is carefully chosen - the same way that valve stacks are designed to ease and impede oil flow in the fork leg, thus tuning air movement. That is very interesting.
    #91
  12. motometal

    motometal i like motorcycles

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    I realize of course in my example that a portable air tank has way more volume than a fork or sub tank...was just illustrating a point. Compression and rebound of the forks happens in a split second.
    #92
  13. meat popsicle

    meat popsicle Ignostic

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    I am no engineer but the same sort of thing is happening down there in the suspension fluid eh. I have never laid eyes on a valve stack... anybody out there care to post the sizes of orifices in fork valves? Of course the density of hydraulic oil is orders of magnitude more dense than air so they would have to be pretty damn large :dunno

    Now that I am way out on this limb, I'll leave it to Zerodog to laugh, give me a shove, and clean up this mess. :augie
    #93
  14. cbig

    cbig Rift- Raft, SCooter Trash

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    so I took the TE610 out, gave it the "curb" test - up, down the curb, at speeds of about 8-10 mph. Then down the street wit some small 2 inch bumps that over time will wear on you if off road.

    I then removed the fork bleeder screws and did it again - much more plush!

    I really didn't think it could affect the short stroke so much but it did. I'm interested in these too...

    Anyone with lots of use on these besides the round the world guy?
    #94
  15. señormoto

    señormoto Supermoto Abuser

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    Seeing as how I didn't read all of the pages of this thread...

    I'm wondering how useful subtanks would be on a 50/50 dirt/road KTM 950SE.

    Anyone, anyone?
    #95
  16. bmwktmbill

    bmwktmbill Traveler

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    Meat, if you go on KTM talk to the suspension forum a breakdown of our forks including the valves is shown in detail in a pinned thread(the valves are shown assembled and disassembled.
    You will understand much more if you spend an hour with that thread...alsoa great overview on the WP fork and how to modify it, is posted on the Husaberg site.

    If you want to lose several months and become an expert because you've got the suspension bug...which I suspect you have, go back to the first post on the KTM talk suspension forum and start reading forward to the present.

    After you get all done with that you will realize why I say Z-dog is a fucking genius.
    You guys are picking at what few secrets he has.
    I always thought the right sized orifice was important.
    b.
    #96
  17. motometal

    motometal i like motorcycles

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    I don't mean to pick, but I feel I have the right to question the engineering aspect of a product, or more accurately...try to provoke thought and discussion on the physics involved with how things work. This tends to happen when pictures and details about a product are posted. As far as secrets, I would doubt Zerodog would want to post any real trade secrets that set his product apart from others. The workmanship looks great to me. Sub tanks have been around for awhile (years), although no doubt the design details vary somewhat from one mfg to another.
    #97
  18. meat popsicle

    meat popsicle Ignostic

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    I thought he tried to answer you, and I just added a bit more info - for you. :scratch Sounds like the "air valve" is designed to tune the airflow between the subtanks and fork bodies.
    #98
  19. bmwktmbill

    bmwktmbill Traveler

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    Hey guys,
    I was totally kidding with you.
    Very sorry for any misunderstanding.
    Man, I want to know the answers just like everyone else.
    And I despise secrecy.
    I can barely read the KTMtalk suspension forum for all the bullshit that goes on ever there among the racers.

    Rob is the most open suspension tuner doing professional work.
    He is a LC4 specialist.
    Most of the shops really tend to be assholes when you ask them what is going on and the tuners are not riders, they are trolls.

    We are not racers.
    We are a brotherhood of adventure riders and Rob is one of us.
    bill.
    #99
  20. tirebiter

    tirebiter Been here awhile

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    I ordered the deluxe kit for my '05 300mxc on monday, hopefully it'll be here tomorrow.
    Gotta nasty ride planned for Sat, can't wait to see how the whole system works..
    Dan