Setting an A5-RR1

[bret]

Ok, my new rear shock arrived. Now what?

There are air valves for 'MP' which I read means "Main Pressure", and 'NP' which I read means "Negative Pressure". I understand I need a pump which will set the pressure and also a gauge that tells me what value it's set to.

So, how do I determine what to set it to?

Cheers,
Bret

 

[DavidJL]

The sheet that comes with the shock recommends 65-150 psi for the main cylinder, with the negative pressure not to exceed the main pressure. You will want to get a shock pump. Obviously, heavier riders will want higher pressure. Since I am heavier, I have been using 150 psi main, and 100 psi negative. Probably best to go by how much sag. I am not sure what the best negative pressure is.

 

[bret]

The shock is installed. The fellow at the bike shop moved the o-ring on the piston to 20% of travel, and I went for a ride including some bumps and some serious hill climbing. On return, the o-ring was in the same place, so he concluded "sag" was correct, and the main pressure was correct.

I noted no "pogo" feeling, no obvious bouncing. If anything, it might be too harsh, rather than bouncy.

So, 95PSI MP, 0psi NP - I weigh about 90Kg these days.

With the "sag" test, I largely trust the MP ("Main Pressure", I interpret). I may try putting some values into NP ("Negative Pressure") to see the effect. I haven't ridden an air shock before, and I haven't ridden a Cruzbike for long.

 

[super slim]

You should have 25% to 30% sag, when you sit on the bike, so lower the main chamber pressure!

On normal riding on a rough bitumen chipseal suburban road, OR bike path with lots of patches, the O ring should be pushed to about 50% of the max shocker travel.

If you drop off a 100 mm (4") gutter from a footpath onto the road, then 75% O ring movement would be expected!
http://www.mtbiking.com.au/workshop/shock-setup-101

I only have a single chamber rear shock on my Softrider, which vastly improved the ride, so no experience with two chambers!



http://www.bentrideronline.com/messageboard/archive/index.php?t-125771.html

I found that some shocks do indeed have a negative chamber which is pressurized to help equalize the shock valve, and improve response over small bumps.

The general approach is to set the negative chamber pressure to zero, sit on the bike and then begin adjusting sag to about 25% of travel and note the Main chamber air pressure value.

Apply that pressure to the negative chamber value to adjust the shock's liveliness.

https://www.pinkbike.com/news/Tech-Tuesday-negative-spring-air-shocks-2012.html

 

[bret]

I've ridden the shock in anger now. I took the pump along - I expect it's a long time of just trying things to get some idea what I'm missing - bad and good.

So, I set the main to 120psi, and the negative to 60psi, and rode around, bike paths, roads, hills. This setting isn't bad. I'll try something else later.

I found myself riding 1 gear higher. Some of that would also come from adding Power Grips: http://cruzbike.com/forum/threads/power-grips-on-a-quest.11811/

 

[Gary123]

Never ride in anger

 

[Giloun]

A5-RR1 setting from the operation manual.

 

[GV_Ottawa]

If this shock is installed upside down such that the MP valve is on the bottom, are you supposed to invert the MP and NP pressures too? Or is MP always where it is labelled regardless of whether it is on top or on the bottom?

 

[Giloun]

MP will always be MP regardless of orientation of the shock.

 

[GV_Ottawa]

Perfect - thank you for the confirmation.

 

[Bikes&Banjos]

I just checked the pressure on my A5-RR1 and there didn't appear to be any pressure in the MP or NP sides. I bought this bike in early December and it's been fairly cold where I'm located near Baltimore. Is it possible that I've never had any air pressure since I got the bike? or maybe I lost pressure in cold weather?

I'm looking for some more "stiffness" in my ride, so I put just under 150 in the MP side and a little less than that on the NP side

How often should I be checking those settings?

 

[benphyr]

Mine doesn’t see below freezing often, however I has seemed to never need any top up. I did check it a couple times in several years and never needed anything. Perhaps pressure was released for shipping?

 

[billyk]

Lots of good advice above.
Especially:
- MP is always main, NP is always negative. Doesn't matter which orientation the thing is.
Do NOT lose track of those caps!
I remove a cap, pump it up, replace the cap, then pump the other. But actually you can recognize which is which by the shape. Take a photo (showing the caps on) with that device you have in your pocket ... Then you'll always have a reference.
- The most important thing is that MP must be larger than NP.
- I judge the right pressure by the o-ring. When I pump it up I put it at the top, and like to see it about halfway down after riding. If it goes more than that it need higher MP. You don't want to bottom it out, I don't think.
- These guys hold pressure for months and thousands of miles (even more km).

 

[Bikes&Banjos]

Lots of good advice above.
Especially:
- MP is always main, NP is always negative. Doesn't matter which orientation the thing is.
Do NOT lose track of those caps!
I remove a cap, pump it up, replace the cap, then pump the other. But actually you can recognize which is which by the shape. Take a photo (showing the caps on) with that device you have in your pocket ... Then you'll always have a reference.
- The most important thing is that MP must be larger than NP.
- I judge the right pressure by the o-ring. When I pump it up I put it at the top, and like to see it about halfway down after riding. If it goes more than that it need higher MP. You don't want to bottom it out, I don't think.
- These guys hold pressure for months and thousands of miles (even more km).

Good tips!

I noticed in the documentation above that it says to lubricate the main shaft after 25-30 hours of use. Does anyone know how to lubricate this shock? or perform any maintenance on it at all?

 

[Bikes&Banjos]

You should have 25% to 30% sa
I found that some shocks do indeed have a negative chamber which is pressurized to help equalize the shock valve, and improve response over small bumps.

The general approach is to set the negative chamber pressure to zero, sit on the bike and then begin adjusting sag to about 25% of travel and note the Main chamber air pressure value.

Apply that pressure to the negative chamber value to adjust the shock's liveliness.

https://www.pinkbike.com/news/Tech-Tuesday-negative-spring-air-shocks-2012.html

I've been fooling around with pressure settings on my A5-RR1 and just want to make sure I sort of understand.

Are you saying that once you find the main chamber pressure setting for the 25% sag and apply that to the negative chamber, that will cause the sag to change again and you'll need to keep applying pressure to the main chamber until you hit 25% again?

 

[billyk]

Are you saying that once you find the main chamber pressure setting for the 25% sag and apply that to the negative chamber, that will cause the sag to change again and you'll need to keep applying pressure to the main chamber until you hit 25% again?

I think you should try this, but ...

- The supposed point of the negative chamber is to reduce rebound. As I understand it, the negative chamber does nothing else. So zero pressure there should only disable this function. I think ...

If that is correct, then the two functions are effectively independent. 25%, whatever (mine is closer to 75%). But please do some testing and let us know.

- How about starting with low-ish (not zero) pressure in the negative side? We don't really know what would happen with zero pressure (google might find you some info). And until you see how low pressure is working, don't start in on jumping curbs.

- @super slim is full of wisdom, but as he says he has experience only with a single-chamber shock. Nuff said.

- I might try these tests myself, but on my 1st-gen Q45, only one of the inlets can be exposed and available. Being able to get to both would make testing much easier.

 

[Bikes&Banjos]

Thanks billyk,

I did experiment with this a little today. I discovered with the negative chamber at zero psi, I had to pump my main chamber to 140 psi for the shock to drop only 25%. (btw... I'm 6'3" 230lbs). So I went back and put 140psi in the negative chamber.

But after doing that, I had a hard time putting enough pressure in the main chamber to get the idle seated drop (o-ring measurement) to only 25%. Most of the references I'm seeing online (and the manual image above) reference keeping the pressure between 65 and 150 in the main chamber. So for my fist try at 150 psi in the main chamber (again with the negative chamber at 140psi), the o-ring dropped more than 50%.

I was a little gun shy to go above 150 psi in the main chamber, but I did push it up to about 165 and tried it again. (with 140psi in the negative chamber) and I was still dropping more than 50%.

I'm a little reluctant to go higher than 165psi in the main chamber, but if anyone can find documentation telling me it's okay to go higher... I'm game.

In the mean time, I just dropped pressure in the negative chamber down to about 110psi, and ultimately I was able to put about 150psi in the main chamber and get the idle seat drop (o-ring measurement) down to about 25%.

I took it out for a spin today and I think it felt pretty good. It was so cold though, I'm not sure I got the best feel for the new shock settings this afternoon. I'll try it again hopefully as it warms up here some more.

 

[rfneep]

The documentation for these particular shocks is pretty thin on the web, but eventually the story becomes clearer.

Basically you are using the large-volume main chamber to mainly set the top-out pressure of the shock. That is set such that regular riding has a max compression drop of about 50% or so of the full motion of the shock piston. You can raise this max deflection (or top-out) to make the bike ride softer by lowering the main pressure, or make the ride stiffer by raising the main pressure and lowering the maximum deflection. As stated, the absolute max main pressure is 180 psi and they recommend a max of around 150 psi. What main chamber pressure you choose is up to you, depending on how soft or hard of a ride you want and the available range of operation of the shock (i.e., the max pressure rating, max cylinder range, etc.).

As I understand it, the negative chamber is not there to control the shock rebound, but in the general literature it is there to reduce the "stiction" of the shock and improve the linearity of the shock response. This "stiction" is the tendency for air shocks to require a kick to overcome friction and get its motion started. Having a low-volume negative chamber effectively lowers the friction that needs to be overcome when activating the shock movement. This smooths out the shock motion, which otherwise would be more jerky.

The sag is there to provide a negative force on the shock so that when you hit a hole the wheel is slightly pushed down faster than the bike and hence the bike gets less impact, and the shock remains active as its goes up and down over bumpy surfaces while lessening the bike motions.

For this particular shock, you want to set the main chamber pressure to get the desired softness or hardness of ride, or in another view set the pressure at which your shock movement tops out - typically 50-75% of total available movement. You want to then set the negative chamber to get the right sag for your desired main chamber pressure. If I recall from the last time I did this, these pressure settings interact so you may have to iterate your values to get where you want to be. These values are referred to as "preload" for sag and "top out" for main pressure in the attached specification sheet.

Ray

 

[Bikes&Banjos]

Thanks for that input Ray.

So If I'm understanding correctly about the negative chamber affecting "stiction" and based on my rides yesterday, I think I'm gonna lower the negative chamber settings a little and then compensate the main chamber pressure to still try and achieve that 25% drop setting when seated at idle.

Just out of curiosity, where did you find reference to the max psi setting in the main chamber being 180? I thought I saw that somewhere before as well, but I couldn't find it as I was adjusting it yesterday

 

[rfneep]

I just took it from the manual (above) that says "Do Not Exceed 180 psi"