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Discussion Starter · #1 ·
RP23 bv has been out for a while now, but I haven't seen anybody post anything about fine tuning the boostvalve pressure.

Can anybody with the right nitrogen gear adjust the boostvalve / Ifp pressure?
What sort of results can I expect?
What are the high and low pressure limits?
Can you substitute higher boostvalve pressure for lower airspring pressure to run more sag with less bottoming?
Does the RP23 boostvalve implementation actually generate significant position sensitive damping resistance to bottoming? Or is it a mild boost in compression damping?
Does it only affect high speed compression damping or is low speed affected too (g-out overtravel resistance)?

Lots of questions but not much info so far makes me think the rp23 bv version is mostly just Fox marketing at work trying to convince us we need to update our suspensions.

I own a RP23 boostvalve and aren't really that happy with it in stock form. Wondering if playing with the bv pressure might make me happier.

If anyone has pictures of the RP23 boostvalve internals I would love to see them.

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Discussion Starter · #4 ·
Please tell me more.
The "boostvalve" apparently is some special valving on the piston that gets stiffer as IFP pressure builds throughout the shocks stroke. From a lot of reports on MTBR the BV style compression damping seems very prone to spiking and seems not be as effective over a wide range of shaft speeds as a traditional velocity sensitive shim stack/high flow piston.

It's real marketed benefit is supposed to be improved resistance to bottoming late in the stroke which allows a lighter/plusher tune initially.

PUSH basically guts the shock and installs their own piston and shim stack matched to you, your frame and riding style. It seems that BV is not tunable enough to warrant their efforts.

What I really wish PUSH offered for the RP23 was an AM version where the ProPedal damping adjustments are converted to pure low speed compression adjustability. I never use PP on my Mach 5 but sometimes would like to be able to adjust how supportive the shock is on a "wallowy" trail with lots of low speed g-outs.

I have moved on to a Monarch Plus RC3 but still have the RP23 BV that came with my bike, and would like to get it setup better.
 

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There are two schools of thinking about MTB suspension. Some prefer no bobbing with a perceived artificial plushness aka blowoff or threshold type valving.

The other camp is for suspension that constantly works, plush and lively.

Some dampers are better at the middle ground, but in turn compromise each end of the spectrum.

Decide what you prefer, which you already mentioned, find a tuner that is capable of building your request. For a good tuner most of this is not that extreme or difficult. This includes making a PP lever design a low speed compression adjuster.

PK
 

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There are two schools of thinking about MTB suspension. Some prefer no bobbing with a perceived artificial plushness aka blowoff or threshold type valving.

The other camp is for suspension that constantly works, plush and lively.

Some dampers are better at the middle ground, but in turn compromise each end of the spectrum.

Decide what you prefer, which you already mentioned, find a tuner that is capable of building your request. For a good tuner most of this is not that extreme or difficult. This includes making a PP lever design a low speed compression adjuster.

PK
Actually a PUSH tune gives you the best of both worlds with no compromises so you can have your cake and eat it too! I've never been disappointed with their air shock tunes.

Have FUN!

G MAN
 

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Discussion Starter · #9 ·
It would be good if we can avoid the whole PUSH VS others argument and focus on the RP23. It turns into a mud slinging rathole of a thread.

Mostly I'm curious about how the bv performs in its stock form and what its limitations are.

Odds are eventually I will have it Pushed but in the meantime I just want to understand what's going on inside this super popular shock.

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I've recently been riding a 2011 BV RP23 on my Anthem X while I service my Magura Hugin. The Hugin has no "platform" but does have LSC/HSC adjustment. I have previously ran the stock Float R and a revalved RP3 on that bike and have compared all of these shocks back-to-back.

You're Mach 5, like the Anthem X probably doesn't need much in the way of a platform to pedal well, and the "propedal" setups on the Float R and RP3 (and probably other Fox non BV shocks) adversely affect rear suspension performance in two circumstances:
  1. when the rear is unloaded, like under heavy braking into rough corners the "platform" will cause the rear to kick; and
  2. on steep rocky out of the saddle climbs where once again the rear is unloaded and will kick on sharp edge rocks and roots instead of hooking up

The Hugin doesn't give me any of these problems, BUT I was really surprised by the 2011 BV RP23 in that it comes very close to the non-platform feel of the Hugin. What it does do even better than the Hugin is offer better bottoming resistance. I thought the Fox BV talk was probably just marketing hype, but on the Anthem X it really is an improvement over previous non BV Fox shocks.

The Anthem X specific RP23 BV has an "L" rebound tune, "F" compression tune and 300psi in the boost valve. I have seen other BV shocks with as little as 225psi in the BV.

You could certainly experiment with some changes in BV pressures. You don't need to use nitrogen if you're just experimenting, although without the proper fill equipment and gauge it will be hard to get the pressures accurate.

You can make a fill needle and use your shock pump - there's a few threads on MTBR on how to do that. Seeing as though your BV shock is essentially a spare and you'll probably send it to PUSH anyway, you've got nothing to loose with a bit of experimentation. Run some different BV pressures and report back.
 

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Discussion Starter · #11 ·
Great post...
Wow 300 psi seems like a lot, buy hey if it feels good. I would think it would be very bottoming resistant with that high of a boostvalve tune. My mach 5 came with 175 psi in the bv.
One thought I had about your positive experience is the leverage ratio factor. I believe the anthem is about 3 to 1, while the mach 5 is in the low 2s. Low leverage ratio means higher shaft speeds which might explain the spiking feeling I get when crossing perpendicular wheel ruts for an example.

I think I will try and get a local shop who rebuilds fox air shocks to up my ifp pressure to 225 from 175 and remove some of the air can shims. Maybe the bv alone will prevent bottoming.

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I've been experimenting on a 2010 rp23 BV on my sf100.

I haven't had the guts to alter the BV yet but have been playing with spacers to reduce the air can volume.
previously at 11mm [240psi] sag on the shock it would blow through the travel on small hits, engaging the PP only made things worse ( feel wise )
At 8mm sag, [265psi] the ride became harsh with poor small bump but better handling of the bigger hits.

I've made a spacer to fit into the shock can above the steel washer/bottom out oring. it fills most of the area and extends a few mm past the washer.

first test ride I tried a few different pressures, 220 was too soft still, 250 too hard ( both were still better by a margin over stock though.
for now I'm going to try 235 and fine tune from there. I get 10mm sag on the shaft and only used half travel over a 1 foot drop at speed ( previously that sag setting would see the indicator oring almost off )

(I'm 95kg FWIW )
 

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I don't have an exact pressure or mod to offer specifically. Tigworld has posted some viable options. In keeping the topic focused, yes, leverage ratio, rider ability to hit good lines, rider ability to apply smooth input, terrain, and ultimately how the damper is designed and setup are all factors. Each one interacts with the others.

Yes altering the pressure can be a huge improvement for some, for others it can be a horrible mistake. To be optimized you need to test.

Te same holds true for the internal valving, fluid type and so forth.

Following Tigworlds recommendation to test various pressures is sound. What you may learn though is that for you and that frame design, it is possible the thing is overdamped. This would not be the first time a production setup missed the mark for valving. That's when a good tuner come comes in.

If you start moving the pressure, I would work a range of 200 minimum to 350 maximum. Altering the main chamber volume is spot on to compliment the new internal pressure ramping.

Yes I have used these methods to compliment some of the revalve and rebuilds when needed by riders that are more picky / in tune with how their bike is performing.

On one of our personal bikes, the Ventana ECDM tandem with a DHX5.0 air, it took a little bit of experimenting to dial it in for the stokers preference. Prior to the DHX air, our early RP23 had some pressure tweaks and shim work also.

Testing takes some time and effort beyond just riding, it will be time well spent once it is sorted.

PK
 

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Actually a PUSH tune gives you the best of both worlds with no compromises so you can have your cake and eat it too! I've never been disappointed with their air shock tunes.

Have FUN!

G MAN
Not bashing nor praising PUSH, like every other tuner in the world, their setup is still a compromise. I don't use PUSH but do know they offer a valuable service for many but not all riders.

When the customer can actually feel a big change, they typically believe it was money well spent. Whether the customer understands suspension and setup enough to know if the entire spectrum of performance increased is another thing.

The OP here seems to have a good grasp on where he would like improvement in his setup. Often, this will give a tuner some concern. Yes by removing the internals and making the damper more active will be a huge change, probably easily felt by the rider. However once past the initial new feel, will other areas of performance fall short.

Every setup is a compromise in some way. Often it is the small detail work that can minimize those compromises. Unfortunately, bicycles run very few shims inside the dampers, have low power output to make things easy to correct and run a very narrow speed spectrum in most cases. Sadly, this will often narrow the tuners ability in making the small changes to take it to the next real level where compromises are minimized.

All the best with your setup GMAN.

The OP has a good plan and should test that first, if more is needed, go inside the damper. Unless absolutely needed for him he should not toss the baby out with the bath water as they say.

Suffice to say, one tiny additional shim made our RP23 go from dog to contender. You just need to know what you want and how to achieve it.

PK
 

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Not bashing nor praising PUSH, like every other tuner in the world, their setup is still a compromise. I don't use PUSH but do know they offer a valuable service for many but not all riders.

When the customer can actually feel a big change, they typically believe it was money well spent. Whether the customer understands suspension and setup enough to know if the entire spectrum of performance increased is another thing.

The OP here seems to have a good grasp on where he would like improvement in his setup. Often, this will give a tuner some concern. Yes by removing the internals and making the damper more active will be a huge change, probably easily felt by the rider. However once past the initial new feel, will other areas of performance fall short.

Every setup is a compromise in some way. Often it is the small detail work that can minimize those compromises. Unfortunately, bicycles run very few shims inside the dampers, have low power output to make things easy to correct and run a very narrow speed spectrum in most cases. Sadly, this will often narrow the tuners ability in making the small changes to take it to the next real level where compromises are minimized.

All the best with your setup GMAN.

The OP has a good plan and should test that first, if more is needed, go inside the damper. Unless absolutely needed for him he should not toss the baby out with the bath water as they say.

Suffice to say, one tiny additional shim made our RP23 go from dog to contender. You just need to know what you want and how to achieve it.

PK
Sure you can tune away all season and maybe get to where you need by winter but I'd rather go with a system that's been tuned on a shock dyno by guys who usually get it right the first time and for certain by the second time.

>>What I really wish PUSH offered for the RP23 was an AM version where the ProPedal damping adjustments are converted to pure low speed compression adjustability. I never use PP on my Mach 5 but sometimes would like to be able to adjust how supportive the shock is on a "wallowy" trail with lots of low speed g-outs.<<

OP- You really should look into the PUSH Monarch RT-AM which does exactly that. It also has an IFP chamber that the HOME tuner can tune using a simple adapter and air shock pump. I sold my RP-23 w/ boost valve and bought the RT-AM for only $110 more than what I got for the Fox. Now THAT was money well spent and I'm riding instead of wrenching!

Have FUN!

G MAN
 

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OP, not bashing PUSH, just get so tired of the marketing hype and BS associated with a dyno. This is somewhat related to your topic but apologies up front for the minor detour.

If the dyno is used for setup, then ask how many inches per second it is capable of. Anything under 100 IPS is not capable of simulating high speed compression spikes. Most companies are usually 40 IPS or less. Pretty much some rolling bumps or pavement setup. Some shops use a multiplier,this can work if the unit has enough HP to drive the suspension components.

Low speed or platform settings are easy to dial in, HSC is very difficult, dyno or not. Even with a dyno, every setting is tested under a rider to optimize it further.

Quoted from JGR

"Many teams have suspension dynos, but what kind? At JGR, our state-of-the-art suspension dyno lets us see the whole picture. Other units will only show a glimpse of what is happening, but our dyno eliminates the guesswork. A successful setting for you may make you more comfortable, help you cut faster lap times, or make the night show. Whether you race cars or motorcycles, it's critical to have the right tools for the job."

If these links play, they should give a good view of a very high performance suspension dyno subjecting damper to some serious IPS. Play number 1, then 2 and so on to see all of it.

JGRMX Suspension and Engine Service's Videos | Facebook

JGRMX Suspension and Engine Service's Videos | Facebook

JGRMX Suspension and Engine Service's Videos | Facebook

JGRMX Suspension and Engine Service's Videos | Facebook

PK
 

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Discussion Starter · #18 ·
Here's a link to an interview with Chris Cocalis of Pivot.
Chris Cocalis Interview | Bicycle Times Magazine
The way he talks it seems like a lot of thought and effort went into the selection and tune of the BV RP23.

DR: Can you talk about the 2010 shock and how that plays into the design?

CC: I talked about the anti-squat, and we actually call it "position sensitive anti-squat" because depending on what gear you're in and what incline you're on, your body mass position changes and it really changes the amount of anti-squat resistance. When you're going downhill and your mass shifts, the anti-squat is much lower that it is when you're cranking up a climb. So we've got a lot of things that we're really optimizing for the different conditions that you would encounter on the bike.

The Fox shocks previous to this year , when you make a valving change in the shock it affects the entire range . The Boost Valve changes it from damping that affects the entire range to ability to control the last 40 percent of the stroke independently. So for this bike, it really allowed us to open up both the compression and rebound damping and lighten them up tremendously, and still have that control through the back end of the stroke, and even through the tail end of the middle. So you don't get this wallowy hammock, but the bike has a higher level of plushness in roots and rock gardens.

DR: Is that Boost Valve rear shock tuning something you worked on with Fox?

CC: Yeah. Fox has had similar technology in their DHX. They have the ability to package it in the RP23-type shock, and they said, "Is this something you could use?" Actually me, Dave Weagle, Hans from Ibis, and Dave Turner were really pushing on Fox to get us some new things that we thought could advance it. I'm sure they would have eventually done something like that, but they kind of shelved the technology a couple times to wait and see.

So you got the tune we design for Pivot and everything. Last year's bike was great, but this just takes things to a whole new level, and kind of follows that philosophy of what we're trying to do, of getting the bike optimized for every type of riding and every situation that you can encounter.

DR: How do they separate that out?

CC: The Boost Valve is actually a separate valve system that gets pressurized. Like on the DHX Air 5.0, you put a shock pump on the reservoir, and the range on that one is anywhere between 150 and 200-something psi. I think the shock has a sticker on it that says what the Boost Valve pressure is. Depending on whatever that separate valve system pressure is set at, it changes that ramp from about 60%-on in the stroke. So, not only were we messing with those pressures, we were also changing the new valve stack and everything.

The shock has the ability to go much lighter on the damping than the previous version shock, so we have the ability on both ends to do things that weren't possible before. Depending on what pressure they pressurize , that affects how that valve opens and ramps up. So now you've got a shock that-the shock previously was mostly speed-sensitive, so depending on how fast you hit a bump and the oils hitting these shims and blowing them open or flexing them-now we have both speed- and position-sensitive valving. The Boost Valve kicks in at a certain point in the travel and can affect that end stroke. How much it affects or how much bottoming control you get is directly affected by how much Boost Valve pressure you put in that shock.

DR: And those vary by bike size?

CC: No, they vary by bike model. So the Mach 5 Boost Valve pressure is different than what we run on a Firebird, different than what we run on a Mach 4 and a Mach 429. Because, as I mentioned, the smaller bikes actually get a different-stroke shock and smaller rear triangle, even though they get the same rear travel. Part of the idea there is that the general valving is tuned for a range of rider weights. So a rider on a medium frame that weighs 180lbs., say they run 160psi in the rear shock. A rider on a small or extra-small frame that weighs 115-120lbs. will run about that same pressure. So the valving and everything works identically, we're just leveraging that shock a little bit more.

And we really do that to a greater degree on the double-extra-small and extra-small Mach 4 frames, where we get women down to 4'11" who weigh 90lbs. Most bikes that are women-specific, even if they went down to that size, the shock just doesn't work for riders of that weight. We make sure that everything from size to size handles that rider weight range.

And in general, between the frame stiffness and the shock pressures, we're a very low leverage-ratio bicycle. So the shock pressures run very low. If you have a big rider, even a 300lb. guy that wants to ride a Pivot, they're not putting 300-plus psi in the rear shock. I'm 200lbs, and I think I run 155psi in that shock. So, it works for a very wide range of riders. The shocks on some bikes are so leveraged that you get anybody really much over 180lbs. and things start to get compromised pretty heavily. That's not the case here.

DR: Is that the larger canister on there too? What's the advantage of going to that versus the standard size?

CC: When we first came out with the Mach 5, we actually had the small can on there and the ramp on it was so much that it felt a whole lot like a Mach 4. You really had to hit something to get the full 5.5" of travel out of the back end. So for the next year, we decided to test more with the big can, and made valving changes that would allow the bike to use the stroke more, but at the same time we made valving changes that wouldn't cause it to just dip into the middle.

And this Boost Valve shock takes that to the next level. We're just able to tune that combination and have a smoother stroke and still get the ramp at the end through damping and not have to compromise the mid-stroke on it.

Yeah, the way the bike is leveraged and everything-when I first designed this bike, the rates were very, very close to the Mach 4, and we wanted to basically make the back end plusher. I actually have customers that are doing 24-hour races but they like the comfort of this bike and they'll either buy a second shock or they'll buy the second can from us-it just unscrews and goes on there-it really gives the bike a racy, cross-county feel. It doesn't sit down into its travel as much.

DR: I can see that if you like to race occasionally, you want it to feel more efficient.

CC: You know on the flip side we have riders ordering large cans for their 429s and putting 120mm forks on it-it's fine. You can put a 150mm fork on this and make it even more trail-bikey and relax the angles even more.
 

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Still though, ultimately, Anti-squat or squat properties are derived from hardpoints on a drawing.

Dynamic anti-squat is about rider and terrain. This leads you back to the beginning, accept the marketing bit, but ultimately get dialed in for you the rider, your terrain and ability.

The best suspension is merely a set of good compromises optimized for that rider on that ride. It has always been this way and always will.

Test, tune, enjoy. If the performance needed requires going inside the damper, and the skills aren't there, work with a good tuner.

Also consider the anti-squat effect is dynamic, Sometimes small changes in riding technique through a certain section or different gear choice will allow better performance of the setup.

All the best with it.

PK
 

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Discussion Starter · #20 ·
Just a quick update.
My plan is not to really spend a lot of money on the RP23 but just to optimize it for what it is. That means really playing with Air Spring Pressure, BV pressure, air can volume, PP, and rebound adjustments. If I spend money on tuning it will likely be on my Monarch Plus shock, as I think it is the better shock overall for the bike but is not optimal with the Medium Compression and Rebound tunes that I am currently running.

I ordered the Fox air can volume reduction kit last week from my LBS. I finally got a chance to throw the RP23 back on with the biggest shim in the main air can in addition to my shim in the HV can.
I pumped it up to 137psi or so and went for a quick ride. Big difference! It's amazing what a couple a psi can do for ride quality.
The reduction in pressure means that I can run lower rebound as recommended by Pivot without getting kicked as much. Also I tried to spike it on repeated hits but couldn't.
I suspect the more progressive spring curve is keeping it out the spikey last 20% of the travel better.
I tried railing down some staircases, which it handled really well. Normally a long stair case would use most of my travel gauged by looking at the o ring. This time I still had 25% left and it felt plusher. I credit the reduced rebound setting and more progression in the air spring.

I will try and hit a trail in a day or two for the true test but it feels good enough that I will leave it on the bike for a couple weeks. If I can't get full travel I might drop the shim down one size.

All in all, I think my issues were more to do with the the air can than damper performance but I won't know till I use it on my regular trails.
 
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