ECDM Rear Suspension Setup -- what's working?
We've had our ECDM since April '06. Over the years we've hunted for the best set up we could get. The trails around Phoenix, AZ tend to be quite rocky and at times harsh.
The bike came with the Fox RP23 shock and 2:1 (4") rockers. Joyce was never happy with the ride. She says that over the same terrain her Santa Cruz Superlight delivered a much more supple ride. (I generally found the ride in front to be quite good on the ECDM). So we bought some 2.5:1 rockers off a logal guy and gave that a whirl. After a while of trying various pressurse and damping settings, I had the shock "factory tuned" at Push Industries, providing our weights, make and model of bike, and trails and style of riding. Still... still hunting for a good ride in back
Our most recent set up has us running 255-270 PSI which gets us .5" sag at the shock.
3 or 4 clicks from foull open on rebound
and RP2 or 3, but we switch to propedal off for descending, generally.
(Team weight: Capt 195/stoker 160)
here's a video of a recent ride
Added the two rear suspension videos we got on New Years.
FWIW these are the same two from the ECDM topic.
http://vimeo.com/18425433 , this is more rocky than the second one
http://vimeo.com/18418786 , flowing single track, softer soil with leaves and roots
Watched the video. Some similarities between your bike, ours and the two setups.
Originally Posted by reamer41
First off, your stokers published weight, is that ready to ride or birthday suit? My stoker is 150 without gear, but rides with a 100 oz Camelback 3/4 full.
In regards to rebound settings, I'm assuming your 3 or 4 clicks is equal to 4 or 5 clicks opened from fully closed. Sorry for asking, seems trivial but I learned and have always counted clicks open, it's more accurate from damper to damper this way.
Do you have the work order from PUSH? Besides a revalve, did Darren do any additional things?
I ask based on you having a large volume, or at least it looks to be a large volume air sleeve.
We have tested both the large and regular volume air sleeves. Watching your video is how the bike felt to me. Lot of base pressure, but marshmallowy soft thru the middle of the stroke. We have stock rockers, your rockers will compound this problem.
For comparison you run 255>270 PSI, @ .5", which I am assuming is shock compression from full extended. With our rockers, large air sleeve, this is a quote from our settings notes. "250PSI is good but has squeak, could be air seal / bushing but too soft in mid stroke...change air canister". So, even though this was a DHX, the large volume can could not be dialed in on our bike. I recall this day, we started with the same PSI as a small can, pedals dragged, added 10 PSI, rode, added 10 more, added 10 more. So we bumped our base pressure up by 30 PSI, but on any terrain with bumps or going over log piles, we blew through the stroke. No amount of damping adjustments could fix it.
I originally thought our damper had to be from a single bike, but seeing yours move around maybe it is for a tandem. Regardless, it is a small air sleeve RP3, initially we had to run the rebound fully closed. After I revalved it, we are able to run it 4 clicks open. The setup sheet for this reads "air pressure 200 PSI. Next were some details on the first time I had the shock opened up and what fluid and internal setting, plus internal PSI was used followed by 200 PSI too soft. 220 PSI liked it at this pressure."
FWIW, our DHX with the same small air sleeve runs 235>237 PSI, but runs much less internal pressure.
My note taker / stoker admitted needing to do a better job, but really she has the bases covered. Unfortunately, I did not log the shim stack dimensions on our RP3, but know I added one shim to help the low speed rebound (which also clips the HS rebound too). I will say I dropped the internal pressure by 50 PSI down to 250PSI. This in my opinion helps take the edge off on those stutter bumps.
Looking back, I'd say borrow or buy a small air sleeve. If you have never been inside a rear damper, these are not ones to learn on. Find a trashed one, learn about it and then have at it if you are comfy with it. Also, the learner shock will give you some shims and parts, which may be handy if you get into it.
The worst problem with these dampers is parts. Fox does not sell every part nor does PUSH. The #1 issue is keeping the internal gas pressure up. The rubber pellet design is a pain. You will need a needle filler to regas the damper.
FWIW, seeing both ends of your bike today has me wondering if when the back gets decent, will the front need more work.
The tandem is a funny bike to get setup. Rear has a load of mechanical grip, yet can slide or spin the tire. Unfortunately, the front does not have the same grip bias. Bottom line for us was that once the rear end worked, the front would not hold a line. The front tire would work fine to a certain point and then just slide with the wheel turned. Same front tire and wheel, different fork, now we have grip.
Last edited by PMK; 01-17-2011 at 04:44 AM.
Stoker is about 160 in birthday suit, but in light XC type garb and waist pack w/light load. Maybe +5 o 10 at most.
Originally Posted by PMK
As to rebound: yes 4-5 clicks from closed (or slow) is what we have been running. But we've bracketed from full open and full closed.
I don't have the work order from Push, but I'll be talking to them tomorrow or the next day. I'll see if they can provide it or valving info.
I do have the large volume sleeve, as supplied when I bought the bike from MTBTandems. I have an RP23 with the small sleeve on my Superlight. I could either sub the whole shock, or swap the air sleeve and see how it rides. I never ride both bikes at the same time!
Yes, the .5" sag is from full extended. The shock has a total of 2" stroke. While the static sag is .5, from watching the vid it looks like it's riding lower than that generally.
I'd never considered opening the damper on these shocks. How do you re-pressurize them? Do you need a nitrogen tank? I'm not afraid of it, conceptually. I just have no real starting point. I've got an old Float I can open if needed. Do you know of any reference material on opening, and reassembling these shocks?
I think I'll be sending the shock back to Push for an overhaul as the pro-pedal seems to have lost its platform.
In your video I noticed some side-to-side sway or flex (at the rear axle) that I saw and was startled at in my video. Normal flex, I guess.
Interesting comment about the front traction. The only times we've "crashed" was due to the front tire washing out.
Just don't tell me to buy a $1600 fork. Just can't do that right now!
If you plan to rest with a smaller air sleeve, be certain that the length is proper. Outside of that, don't count on a shock from a single doing much more than fitting.
Originally Posted by reamer41
In regards to the fork, consider that most Bombers are pretty lively and will need some additional work to give it fake PP.
Reamer, and others with the large volume air sleeve, I forgot about this simple volume change mod. Several topics on the mod, didn't read each, but possibly one will give the goods up.
DHX air upgraded with the RP3 air sleeve
Last edited by PMK; 01-18-2011 at 04:59 AM.
Paul, Reamer, all,
This thread is over my head. How do I get more educated about shock setup? We have an ECdM with an RP2 and after initial setup, my stoker has no real complaints so I don't have much data to work with. From that I'd assume we have it set up well enough to work, but I can't imagine we have it dialed in just from dumb luck.
I am mechanically inclined - I do all the maintenance and repair of the bike and have put seal kits in the RP2. Watching Reamer's/Paul's videos of the rear end, all I see is a rear shock compressing due to trail input. Is the video alone enough to tell what's what, or would I need stoker input?
This is a great set of questions.
Originally Posted by Okayfine
How do you learn more about suspension, truth be told, there is a very good book released last year. Paul Thede of Race Tech, the motorcycle suspension company wrote it. Might want to give it a look if you ever visit a Barnes and Noble. Books are fine, but to learn beyond the book you MUST start experimenting. There are some basics that always work, beyond that, each team is different, we all ride different terrain and preferences will be close, though often subtlety different.
If your stoker has no complaints, several things could be happening. 1) The bike is spot on. 2) The stoker is very adaptable, which is extremely possible. 3) The stoker doesn't know any better.
The best thing to do is to make some written notes of your existing setup. Then make drastic changes, ride and feel the differences. Talk to the stoker and ask their opinion of how the bike is reacting or feels. Make a big adjustment the opposite way. Ride again.
Now try and fine tune it for the two of you.
Our bike was setup without video. My stoker has dumb thumbs when it comes to adjusting shock clickers or the outside brake pad adjuster on out BB7 brakes. My stoker is in tune with the bike, she notices it sliding around, stepping out a lot at times, but also has basic terms for when we set it up. Too bouncy, hurts my back on bumps, etc.
Normally, when we dial in a new setup, first is to get it sprung correctly. We'll set the shock pressure to what seems good for static ride height (aka Sag). Then the bike gets ridden, the setup is discussed. Even if we both like it, the setup is changed. This is evaluated. It doesn't take long to find the air pressure settings. Most times this final pressure, and sometimes the test pressures are logged with notes.
The external damping clickers come next. Most often, the rear is initially setup by rolling with the pedals flat and her working the suspension by bouncing the bike. When we find a clicker setting that she likes, we ride it. Again we make changes, even if we have no complaints.
The compression or PP is set next, same method.
Changing compression, PP, or pressure all intertwine. As they dial in, small tweaks may add the final adjustment for the best setup.
Unfortunately, trails and weather are dynamic, so for us, each ride may see a click one way or another once rolling, in the end though we still have to adapt.
I'm not sure how, but Jeanne is also able to sense fork setting changes. Most often she is in tune with how the bike corners. She doesn't know what's wrong, but sometimes asks about why this or that. She knows I have no concern about turning clickers while rolling.
So back to the video, I don't just look at the wheel movement. The frame and how upset it becomes from the bumps. How lively is the wheels action.
Thing about suspension tuning, it's a moving target. What I see on Reamers setup, these could be changes that we would love, but they may hate. So much comes down to testing.
If you have the means to take some video, post it. Maybe you will see you are spot on. Do you need stoker input, no, but it does help.
Okayfine, I'm still trying to get educated, myself. It can be a little overwhelming. The first fork I tried to rebuild, a 1999 SID -- I couldn't get it apart or close it up and the shop ended up sending it to RockShok to fix it. So I'm a little cautious.
My Junior T fokr is super-simple, and air sleeve maintenance is simple on these Float shocks is very easy. I'd never considered opening the rear damper until PK mentioned it. Now I'm curious.
PK, a question on the large v. small sleeve: Wouldn't the large sleeve be less progressive? Wouldn't the spring rate in the small sleeve ramp up faster? It seems that we are not getting the last half-inch of shock stroke as it is -- a more linear rate would be better, I would think.
Or is the compression damping the issue?
Now Joyce is reminding me that we didn't used to have the less-than-full travel issue. Thant both before and after "pushing" the shock the ride has been "too bouncy" and too harsh.
I haven't talked to Push or done anything since my previous post....
Guys, first off, I am not saying the first course of action is going to the shocks internals. I have been working on gas charged dampers since the mid 1970's.
The emphasis is on getting your best compromise for the setup. Even if you think the settings are perfect...the weather will change and they could be better.
If your shock has the ability, learning to dial it in just takes a little bit of time and some practice. If your team, or you as an individual rider is one that must be on the gas every moment of every ride, and has little patience to do more than turn the cranks, suspension adjustments aren't for you.
Optimizing clickers, air pressure, or spring rates and preload can transform the as delivered stuff into pretty darn good many times.
Yes some suspension is super simple and can work very well, other stuff is very complicated and delicate with limited parts. Let's do the easy stuff first.
Honest and true, the rear shock video of ours, the only change made to that shock is the air sleeve size. The rest was merely optimizing the clickers with the current internal shim stacks. When the shock is pulled apart for a rebuild, I have one internal shim change I want to do, we will then dial it back in and with luck have it good for a long time. In regards to out FOX40 fork, the changes from as delivered, heavier springs, travel reduced, lube fluid replaced. The damper is untouched, the settings internally from FOX are not bad, but it took a while to "break in" before the settings could be optimized.
So you trashed a SID, many were not that good anyway, but did you learn anything besides not to work on SIDs?
Originally Posted by reamer41
Your Bomber is, as you say simple, but they are still a good platform. Last week I worked with a local guy on his Asian Marzocchi Bomber. Took a bit but the return phone call yesterday said he was happy with the changes.
"PK, a question on the large v. small sleeve: Wouldn't the large sleeve be less progressive? Wouldn't the spring rate in the small sleeve ramp up faster? It seems that we are not getting the last half-inch of shock stroke as it is -- a more linear rate would be better, I would think."
Yes small sleeve is more progressive.
Yes small sleeve will ramp faster with more end pressure, based on the same initial base pressure.
More linear is good for light teams or non aggressive riding style, or bikes that have long travel and need super compliant settings (True DH).
Not getting the last 1/2 inch of travel. To explain further, internally, the shock has an IFP (internal floating piston). This piston separates the internal gas charge from the oil, providing consistent damping. As you bottom out, the 300 PSI base charge on the IFP also ramps up.
With adjustable pressure shocks like the DHX5.0 they call this the "Boost Valve". We use the pressure on the IFP and the IFP rezzy volume to tune these settings.
On the RP series, these adjustments don't exist, and the window to change the pressure is small since there is no piggyback rezzy.
So, lets just say, you two are a "standard size team of standard ability". You adjust your shock pressure to a value, based on how much sag you see on the shock body. This is good. Now consider the progression effect of the air sleeve volume. Your base pressure is pumped in with the shock at full extension. When you check sag, the shock is partially compressed, therefore progression of the air spring rate has begun.
A large volume air can will often require more base pressure to achieve proper sag.
Going further, with the small can, the progression through the mid stroke will support the bike better. This noticed especially when cornering, or on some "G outs", or rolling bumps (whoop like features). The large air sleeve often has less mid stroke support of the bike, and in turn you here folks say "it blew through the stroke". I refer to this as the bike wallows around.
Going even further, towards bottoming. First off, the FOX RP and DHX is a shock you do not want to bottom out. The bottoming cushion is merely an "O"ring, and doesn't do a good job. True bottom out on an RP or DHX air is bad for the shock, frame, linkage, and the riders spine.
So your large air sleeve is compressing the pressure is rising, and hopefully you will light "kiss" the bottoming cushion. Bottoming peak loads are seen by several things. One is how fast is the shock compressing. This is primarily controlled internally by the fluid and shims. Next is how much pressure and ramp up is on the IFP. Third is peak air sleeve pressure.
So Reamer, you say the last 1/2 inch of shock travel is not being utilized...Can we assume then, that with your long travel rocker you have a 2.5:1 leverage ratio (5 inch wheel travel, 2 inch shock travel, 5 / 2 = 2.5 ). This translates to every inch of shock compression gives 2.5 inch of wheel travel. We run low leverage linkage, 4 inch of travel with 2 inch of shock stroke or a 2:1 leverage ratio.
So if our bike uses 99.9% of the travel (remember I don't like hitting the "O"ring cushion), we have 4" of wheel movement to absorb the bump.
Your setup, is 1/2 from bottoming, or 1.5" of shock stroke. So then 2.5 (leverage ratio) x 1.5 inch of shock stroke says you have used approximately 3.75 inch of wheel travel.
Stay with me...I watched your video and noticed you made specific comments at certain points. I also watched the shocks movements.
One comment made, the shock topped out (extended quickly followed by a possible "clunk"). It is possible that air has worked it's way into the shocks internals mixing with the fluid to cause this. Things is, the shock was definitely running so the fluid should be emulsified if air is inside. You could have the rebound set to quickly. Or, remember with the large air sleeve, you need more base spring pressure, this can be a big factor on top out. When you ride a coil spring type shock off road, you strive for a proper spring rate with minimal preload.
You specifically mentioned the chatter was often felt. A large air sleeve, will settle lower in the stroke under true riding conditions. Depending upon where the bike settles, and how large the chatter features are, this can position the linkage in a less than optimum position to be soft and compliant. The lack of ramp up on the air pressure further lets the bike wallow, often getting into firmer pressures for bottoming. For stutter bumps, the chassis needs to ride higher in the shocks stroke to optimize spring rate and linkage settings.
"Or is the compression damping the issue?"
For small bump compliance, you want to run the least amount of compression damping. Unfortunately, we also like the stability of having PP, this is a balance for each team to find. I will say that I do not like to see full suspension bikes in PP lockout except on pavement or smooth dirt roads. Most frame builders also support this.
"Now Joyce is reminding me that we didn't used to have the less-than-full travel issue. Thant both before and after "pushing" the shock the ride has been "too bouncy" and too harsh."
Can you give details of when or what conditions offered full travel.
The before and after being harsh and bouncy...I wold lean towards a smaller air sleeve volume ( just install the plastic sheet as mentioned in the link), AND ride up and down a smooth trail or street. With you seated, have your stoker stand an bounce up and down, using knee movement compress and unload the suspension. Dial in rebound until noticeably slow, as in the bike won't follow her movements upward. Then open the clicker one click and test.
Consider all events, the small sleeve will have less base pressure but the same approximate sag dimension. Hopefully less topping out, more compliance on small bumps, with decent bottoming control from less base pressure. The bike will sit taller in the stroke, which should be more compliant on stutter bumps. Added rebound should make pedal bob less noticed allowing possibly one setting of PP2.
Hold off on talking with Darren at Push, let's see if we are steering a good course.
Apologies for the long reply, I tried to explain all the whys and what ifs.
Last edited by PMK; 01-19-2011 at 10:39 AM.
Paul, thank you for your comments. That methodical approach is very sensical. We will be moving to an RP23 in a couple weeks, so that presents the perfect opportunity to go through all the adjustments.
Do you have any experience to know if our rebound and pressure settings for the RP2 will transfer straight to the RP23? That would be helpful to give a common baseline.
I pulled the air sleeve off today. It had a load of oil from the blown damper. That would explain the last 1/2 inch of shock travel never compressing -- the air sleeve was filled with oil! So I'm sending the shock in for overhaul.
I swapped my small sleeve RP23 from the Superlight onto the Ventana. Needed a lot more air -- 285 seemed about right for 1/2" sag. 290psi might be better. But I had to back the damper off 1 click from closed. At 2 clicks from closed it was definitely under damped. We got some squeaking from the shock -- whats that?
In general Joyce says it was much better than the blown shock. I took some video, but haven't looked at it yet.
Long story short -- its hard to fine tune a blown shock. The single-bike shock isn't ideal but its better than what we had been riding.
Originally Posted by Okayfine
I'm glad the writing was understandable. Hopefully it helped a little.
As for the RP2 to RP23, the logical answer is yes. Truth be told, it will be close until the suspension breaks in.
The thing to toss a curve ball is that, and I'm assuming this is in regards to the S&S, that should have a 2011, or depending upon Ventanas shock inventory a 2010, but both of these will have the boost valve circuit. This is something that has been on the downhill shocks for a while.
The circuit will add bottoming resistance based on how compressed the damper is.
This may have an effect on the pressures you want to run. Still they should be close.
The pressure numbers seem pretty high to me. Not sure why.
Originally Posted by reamer41
Curious if you sent it back to PUSH or somewhere else.
Yes it is extremely difficult to tune a shock that has lost it's fluid.
Not uncommon though, and you may not be aware of this, but often these air shocks have air forced into them past the main seal. This too makes tuning consistently, difficult.
Guys and girls, I've been working on suspension systems for a long time...I also get lazy sometimes...While looking for some Fox decals, I stumbled upon this.
As a suspension tuner, most of us would not claim to owning the setup procedures. There are basics we follow that work very well. I had never seen the Fox video until today, it is though how tuners have dialed motorcycles and bikes in
for a long long time.
Follow the sequence, Preload, Rebound, Compression. A change to any setting may require a small change to optimize the others.
The Fox video, and the format they present it in seemed very good for the portion I watched.
I'll still gladly help, however this may help some of you get a better understanding of how as a tuner, we sort out settings. As the Fox guy mentions, most often this works for many riders / teams. I do know that if you want more, often it involves going to the internals.
When you get to the topic Fox calls "Bracketing" I would rather see you do your bracketing on smoother level terrain initially. Their idea of running the limits while riding could cause some handling concerns. In other words, get your settings close before hitting a trail, then dial them in.
Remember, front to rear suspension balance is very important, to some extent this will need to e a team effort.
I did not watch the entire video set, but will when I have some time. If I notice any items more Tandemy, or not Tandemy, I'll try and point them out.
Have Fun, and welcome to my world.
Thanks so much for these links. I love things that give a sequential procedure. I have certainly learned a bunch from all your various posts and your help to others but this sort of ties it all together.
Thanks again for your time and efforts
Thanks again for all your input.
The small sleeve on the Superlight RP23 seems OK. We're still starting with a similar PSI. Haven't got it dialed, yet -- hopefully I'll get the other shock back soon enough that I won't have to. With the damping knob 1 cloick from closed the shock squeeks! (Under both compression, I think, and rebound.) Do you know what causes this? Is it harmful to the shock?
With the small sleeve shock we're back to 285psi for 25% sag. We tried 270 PSi and static sag was only slightly more, but I think 285 is closer and supports the bike better. I think it best to disregard my past posts regarding shock PSI as the air sleeve was half full of oil.
The thread on tuning the air volume with non-compressible material is interesting and very straight forward. When I get my shock back I will experiment with this. Our tuning over time has been somewhat complicated as team weight has dropped (Capt lost about 30-40 lbs), so I've found less air was needed in the rear shock -- but now it turns out that this was at least partially due to the sleeve filling with oil.
As to bottoming or using 99% stroke-- Looking back, 18-24" near-vertical drops, and maybe big g-out type dips. Short & steep whoops on the motorcycle trails is another possibility. The tandem can really be a handful in those whoops! PP is a big help there, and I'm looking forward to seeing how the bike manages them with the newly adjusted fork. And overhauled shock.
We often use the PP switch-- turning it off for rough descents (and the chatter section in the video), and on for smooth-trail pedaling and climbs. Most of the trails are so rocky here. On smoother trails we often leave the PP on.
Originally Posted by PMK
I'll (we'll) try this. In the past I had used a bracketing method on a piece of trail to dial in (guess at) a good damping setting. This sounds like an easy way to find a good starting point. Not to say that I wouldn't still bracket on the trail, but this makes sense.
Originally Posted by PMK
No need for the apology! I really appreciate your taking the time to share you knowledge and help me get a mental handle on some of these things.
Originally Posted by PMK
I forgot you have LT linkage. Therefore higher pressure.
Increase travel 25%, increase pressure 25%. Pressure sounds reasonable.
The squeaking could be the seals, it can also be the fluid sliding between shims.
Did you pull the air sleeve and see if the Santa Cruz damper had air inside the damper, felt and heard as a hiss with the shock extending on it's own from the internal gas pressure when it is upright.
I sent it back to Push.
Originally Posted by PMK
(thoughts? feel free to PM me.)
I was not aware that the shocks could get air forced into them. And I have heard, in the past, anyway, that hiss. I didn't know it was air in the damper.
I haven't done a thing since the ride with the Superlight's RP23. I've been out of town. Home tonight!
If there is air in there is there any remedy?