RS Revelation RL Brake Dive- Mtbr.com
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  1. #1
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    RS Revelation RL Brake Dive

    Suspension experts... I'm getting pretty heavy brake dive at times. My current solution has been running it at high pressures and the negative spring at 5-10psi higher. Fork is supple on the chatter and progressive, works fairly well but the compromise is that it's typically 3/4" shy of getting full travel (measuring crown to o-ring distance) despite taking some pretty hard hits. This is due to high positive pressure, not related to negative spring reduction in travel.

    Is brake dive just a fact of life with the lack of slow speed compression adjustment? Any tweaks I can do to the valving, compression lockout, etc while open for oil/service (haven't serviced a fork in 10+ years, but have been told it's not too difficult for mech inclined).

    For reference: 2011 RockShox Revelation RL, Dual Air, 140mm travel, Motion Control damper, rebound and compression adj. w/LO

    190lbs / + 125psi / - 135psi

  2. #2
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    Too much negative. Go 5-10psi UNDER positive. And I would drop down to 90psi+ and 80psi-.

    I weigh about what you weigh, run a little compression damping and only about 68psi in my solo air Revelation.

    mk
    TrailWerks Cyclery
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  3. #3
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    Wow, so I just picked up a 2012 RLT Dual Air and am slowly working towards finishing the bike it will go on. I weigh the same as the OP, maybe 200 kitted up, and their chart says the pressure ranges that the OP has stated.

    I have read that their charts are off but didn't realize by that much. Is this statement true?

  4. #4
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    To handle brake dive, the fork needs the proper amount of both lsc AND spring force. Damping slows down the weight transfer, but ultimately spring force supports/counters the weight transfer. The longer you are on the brakes, the less effect damping has on dive. You can partially close the damper to adjust lsc. Running the air closer to even or even lower neg will provide more force in the initial to mid portion of the stroke. But, this has a huge effect on small bump compliance. I always had to live with a little excessive dive in order to get decent small bump out of dual air RS forks.

    This chart is a good visual for the relation between pos/neg and the effect on the entire stroke. You want more midstroke force to combat dive.
    84766d1119048722-reba-dual-air-spring-rates-air-graph-3.jpg

    Keep in mind that as you bias more towards pos or neg, you have to shift both pressures accordingly to maintain sag. Also, when running higher neg, make sure you always bleed it to below pos before making adjustments to the pos, and then set neg last.

  5. #5
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    Quote Originally Posted by ktm520 View Post
    You can partially close the damper to adjust lsc.
    My fork has a compression lockout... and it seems that it's either on/off through a quick garage compression test. Have I not done diligent enough testing out on the trail to feel there's an effective adjustment?

    Thanks heaps for the spring rate graph. Kind of confirms what I'm doing and why.

  6. #6
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    Quote Originally Posted by ktm520 View Post
    Running the air closer to even or even lower neg will provide more force in the initial to mid portion of the stroke.
    Correction, as this statement is miss leading and not completely accurate. Changing the bias of neg/pos basically changes the slope of the entire curve, ie. either makes it more or less progressive. For example, say -70/+70 and -105/+90 have equal sag, which is roughly accurate from memory of setups I've tried in the past. The later, neg biased, will be more progressive and therefore have more midstroke support, equal less dive. The key here is that sag is the same.

  7. #7
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    Quote Originally Posted by EatsDirt View Post
    My fork has a compression lockout... and it seems that it's either on/off through a quick garage compression test. Have I not done diligent enough testing out on the trail to feel there's an effective adjustment?
    Do you have a remote on the bar, or a knob on the crown? With the later, you have about a 1/4 turn of lsc adjustment. It can be hard to distinguish with a garage bounce test depending on how sensitive your hand dyno is. Next ride, try bouncing back and forth between open and half closed.

    Oh, does it have a floodgate adjustment in the center of the knob? Ifso, it could be set too soft which effects the overall adjustment range.

  8. #8
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    Here's a better graph that shows different setups at equal sag.
    https://fcdn.mtbr.com/attachments/sh...ir-graph-4.jpg

  9. #9
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    It has knob on top of crown with no additional adjustment knob. I'll give it a shot on a ride and see if it helps.

    Thanks for all the info!

  10. #10
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    I don't know how that graph was calculated, but, in my experience i get MORE brake dive when i run higher negative pressure. Anytime i make my suspension more sensitive to small bumps, it allows the initial movement of the fork to require less force. Hit the brakes and it instantly dips down.

  11. #11
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    Were you running the same sag with both setups? I've found that most folks that try neg bias don't increase the pos accordingly to bring the sag back into check. And on the flip, those running a pos biased setup run very little sag. This is usually the disconnect when folks compare setup.

    Part of why a neg biased setup has better small bump is due to the lower spring force below the sag point.

    Physics are physics. The absolute numbers on those charts may not be accurate, but it really doesn't matter. The general shape of the curve and the change in slope illustrates the response. The pos pressure sets the end rate. Work your way back from there. There are a ton of threads beating this topic to death going back to '07'ish.

  12. #12
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    Quote Originally Posted by EatsDirt View Post
    It has knob on top of crown with no additional adjustment knob. I'll give it a shot on a ride and see if it helps.

    Thanks for all the info!
    EDIT: I am idiot. On the compression lockout knob, there's what looks to be a cap that says "gate" with circlip under it. I've read mentions of gate adjust but I'm not familiar with it's function.

    I'll pop the cap off and dig around for info on gate when I have time... unless of course someone would like to explain it?

  13. #13
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    You use a hex key (2.5 or 3mm?) to adjust the gate. CW is firmer. I seem to remember there be approx 4 turns of total adjustment. On the firm side, you will get a "lockout" when lsc is closed. On the soft side, it is more like a finer lsc adjustment. I always ran mine full soft.

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