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  1. #1
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    Manitou Headz: Air shock IFP tuning questions

    Mullen, Dougal and co,

    Winter riding seems to be about done here, and I want to switch back to my air radium from my avalanched swinger coil. My bike (a nickel) has a regressive to progressive ratio, and there is alot of ramp-up at the end of stroke.

    It doesn't ride poorly, but if I have the bike set up to run at 145mm travel, I wouldn't mind having it available.

    With the pressure out of the air can, the shock "bottoms" at about 51-52mm. It is a 57mm shock, or its supposed to be. I ordered it new, and that is what I ordered, and what the packaging said.

    I'm thinking that lowering the ifp pressure a bit will give me a more linear stroke. I might have to run some more air pressure, but I'm fine with that. At 180 lb, I"m running 110psi in the shock to get less than 20% sag.

    With the air can off, compressing the damper, I have to put A LOT of weight on the shaft to get it to move. Much more than on a mid tune fox, or any of my coil shocks (RC4, new van RC, swinger) without a spring on them. This all leads me to believe the IFP pressure might be too high from the factory.

    So, what do you guys recommend for an IFP pressure? I have the 3-1 tool.

    This is on a new manitou radium RL. No SPV. Aside from some new valving and standard shock eyelets, it looks JUST like a S-type SRL.

    I'm thinking 150psi is a good place to start, as that is what was factory recommended for the S type in the 2007 service manual.

    I just don't want to go too low and have to take the damn thing apart and bleed it. It's really running exceptionally well otherwise.

    Also, I would like to pick up a HV (or DC in manitou speak) aircan for it. I think a swinger, or older S type air can would fit. Anyone here holding?

    Thanks all,
    H.

  2. #2
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    You could look for the DC air can for an Evolver, but I cannot guarantee it would fit.
    My Radium has a rubber bottom out bumper that compresses quite a long way! The rubber is quite soft and sculpted, so I would not be surprised of the last 5mm can be found in compressing that ring. And don't forget that full extention is only achieved by compressing the negative elastomer, which should be done by pressurizing the main air can to >80psi.
    Furthermore, I think that using the lockout feature with the IFP at low pressures (<300psi) will create a lot of cavitation behind the piston, which can damage parts, and suck in air from the aircan-seal.

  3. #3
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    The last 4mm of stroke your missing is probably the bottom out bumper. When the air is out, push down hard and see if you get a little more. If it does and you're getting 51-52mm of the stroke on an average ride, consider it a light bottom out. and the last few mm would be a harsh bottom out.

    In non spv shocks, playing with IFP pressures is not going to make much of a change. Shim based shocks tend to run close to the lowest pressure possible to stop cavitation anyway, so you shouldn't go to much lower than what should be in there now. I would email Manitou and see if you can get the recommended IFP pressures and what comes stock in the shock(ask about the air can too, not sure if the changed the thread pitch of stanchion diameter). If you really want to make a change,(air can would be the best/first option), making the IFP volume larger by raising the IFP depth is a better option. Then you can run the correct pressure to stop cavitation and decrease the ramp up in the IFP chamber. This would require a full rebuild though.

    150psi is pretty low by the way. I would not go below 250psi unless you check with Manitou. Even that may be too low.
    Hope that helps.

  4. #4
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    thanks guys. Shock had 230 psi according to my gauge in there. Rode stiff as a brick, and felt like it hit a wall half way thru the travel. Lowered it down to 210, shock feels more linear thru most of the stroke before it ramps up quickly (cycling without aircan on)

    Took it out for a hard ride today, no cavitation. Full travel event still yields about 52mm of travel...which is fine. Call it a soft bottom out, it's better than beating the piss out of the shock. Bike rode great and stayed up in its travel, even though I was beating the crap out of it chasing my buddies around on a revolt, wilson and dhr down a jumpy hardpack trail.

    Mullen, I came up with the 150 number per a post you made that I pulled up searching manitou ifp psi......and from their tech doc on rebuilding the damper (cited all radium and s type as 150psi ifp/170 psi )

    You think 210 is a safe operating range?

    Going off of what I remember from messing with a monarch, I thought the important part was to run more pressure in the IFP than in the main can. What would make the radium different from the monarch in this regard?

    At 185lb with gear, I'm running 125psi to get ~25% sag. That's what I based the 200psi or greater in the ifp off of, assuming that 75 psi was a great enough difference to prevent cavitation.

    If 200-210psi won't hurt anything, I'll leave it there. If there is a danger of cavitation, I'll bump it back up.

    I never run the bike with the lockout, FWIW.

    Certainly made the shock more rising rate compliant though. This thing rips ridden hard.

  5. #5
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    Out of order for some reason
    Last edited by mullen119; 04-07-2013 at 04:41 PM.

  6. #6
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    S type shocks use SPV dont they? SPV shocks run much lower IFP pressures then Shimmed shocks. For example, a boost valve fox shock runs 175 to 225psi. But a non boost valve fox shock runs 350-400psi

    How did you check the IFP pressure? If you stick your pump on the shock and check it that way, you are going to lose 40-50PSI from the air filling the pump.

    FWIW, if a shock is cavitating, you should be able to hear it after a rough section of riding. Once the oil starts to foam, the damping gets louder. If you feel comfortable riding it at 210 and dont think its cavitating, then ride it. Probably worth sending Manitou a quick email asking for the operating range just to be safe.

  7. #7
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    Dammit mullen,
    You make too much sense. I never know how much pressure drop to assume when screwing a pump on. I'll call manitou up, but sometimes that's easy, sometimes its not. Unless their shock engineer is in the house, it's kinda hard to get an answer on that kind of stuff. On the up side, when you do get to talk to him, it's very enlightening.

    I'll see how much the pressure drop is when I put the pump back on it tonight, and will re-pressure-ize closer to the original range it came at. I'll shoot for 10-20psi less than factory, hoping that gets rid of the super ramp up, but provides a nice margin of error. The consensus then is that 250psi is usually safe?

    But yeah, for all intensive purposes, the shock is running better now. Still full function, I didn't have to alter the rebound range more than a click or two, main can psi, or anything like that. Effectively made the shock play nicer on frames that are L/M tune friendly, instead of M/H tune friendly.

    If I had this thing in stock form on my Remedy or Prophet MX when I had it, it would have been the answer to all my previous shock fiddling.

    This is the 2013 radium RL, so no spv, all shim damped. 10mm stanchion for increased oil capacity, for a very simple shock I like it so far.

    H

  8. #8
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    Curnett style pistons increase comp damping with increased ifp pressure. Rebound will not cavitate with low pressure cause of the low comp damping. The oil can pass quickly through the piston so no rebound cavitation with low pressure.

    On non-curnett shocks the ifp pressure need to be high enough to get the damper oil to the rebound side without cavitation. One might not even be aware of low ifp pressure until a hard hit and the rear kicks back. One can adjust the ifp with a given comp damping I suppose but if one has ever had a shock kick back hard they will then realize the importance of proper ifp pressure.

    Air in the oil is not the same as cavitation.
    lean forward

  9. #9
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    You can lose a good amount of pressure when attaching a pump to the IFP since the volume is so small. Much more than the 5-10psi you lose when attaching it to the main chamber. I would guess if your gauge read 230psi, the stock pressure would be around 300psi. 250psi would probably be safe if you dont use the lock out or use it in very small doses.

    What I would do is run it at the highest pressure that gives you the feel you are looking for. Start at 300psi and go back 10psi at a time until you get a feel that you like. Hopefully you can get a good feel still at a fairly high pressure

  10. #10
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    excellent advice as always....hopefully I didn't do any harm with this little experiment so far. Shock still runs silently, so I suspect I'm ok.

    I didn't think the difference in feel would be as drastic as it was...and, through most of the stroke, it wasn't But the last bit of stroke was really affected, and the combination of mechanical bottom out combined with the progressivity of the shock was a bit much. I'll pump'er back up and dial back accordingly till I get to 250, and then go as high as I can before adverse ride quality again.

    Pretty pumped to have a shock that, even though it doesn't have all the external bells and whistles, can easily be modded for different ride qualities.

    I would pop the whole thing open, but I don't have shaft clamps small enough to get the tincy damper rod on this.

  11. #11
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    I think the difference is such a drastic change because the you changed the pressure so much.(as much as 100psi) I think you will be in good shape though with a little higher pressure.

    And 1niceride, I never said cavitation was air in the damper. Its just bubbles forming in the oil from agitation

  12. #12
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    Quote Originally Posted by mullen119 View Post

    FWIW, if a shock is cavitating, you should be able to hear it after a rough section of riding. Once the oil starts to foam, the damping gets louder.
    Yea, I misread your post...
    lean forward

  13. #13
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    Quote Originally Posted by mullen119 View Post
    You can lose a good amount of pressure when attaching a pump to the IFP since the volume is so small. Much more than the 5-10psi you lose when attaching it to the main chamber. I would guess if your gauge read 230psi, the stock pressure would be around 300psi. 250psi would probably be safe if you dont use the lock out or use it in very small doses.

    What I would do is run it at the highest pressure that gives you the feel you are looking for. Start at 300psi and go back 10psi at a time until you get a feel that you like. Hopefully you can get a good feel still at a fairly high pressure
    I know this thread is old but I think I have relevant info if anyone is searching about this.

    This thread did caught my attention and I contacted Manitou about the stock IFP pressure and safe range for the Radium Expert (2013), here is the reply I got from them:

    Hi Ric, the stock Psi is 500psi.
    We need to go this high to achieve Lock out.
    You can run down to 100psi if you wish but you will no longer have a true lock out.
    Running around 300-250 you will have a soft and hard compression adjustment and no lock out.


    Colin Powell
    Warranty/ Tech Support
    Phone:888-686-3472
    5800 W. Donges Bay Rd.
    Mequon, WI, 53092
    I think that is pretty interesting, especially the part about running 250-300psi... unless I'm missing something, that basically turns the Radium Expert (lever controls locket) into a Radium Pro (lever controls compression setting).

    Only concern is, how do you get back to 500psi if you depressurize below 300, my shock pump only goes as high as 300psi...

    -- EDIT ----------------------------------
    Regarding putting over 400psi, nevermind, just realiuzed there are shock pump going up to 600:
    High Pressure Fork/Shock Pump 600 psi | SRAM

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