FM036 shock tuning (Rockshox Monarch RT3)

[two-one]

Hi everyone, I just joined this forum, but I've owned my FM036 for two years now, and really enjoy riding it! There are however a few things that bother me about this frame:

• The rear linkage is not very stiff, I'm currently looking for new chainstays with 12x142 axle to replace my current QR chainstays
• The suspension curve is unusual, so the rear shock must be specially tuned to get the most out of the bike, see the data here

So I was wondering what kind of tuning all you FM036-owners have done to get the most out of your rear suspension.

I'm currently using a Rockshox Monarch RT3 from 2013. I like the 3-setting switch, even though I would probably survive just fine with setting it to "open" all the time. But the problem was with the rebound. When I use a pressure that allows me to ride with ~30% sag (while in attack position), I had to close the rebound completely, otherwise the rear end would produce a big kickback, but suppleness over small stuff would disappear.
The reason why the rebound must be completely closed is because the leverage ratio at the end of the travel is more than 3:1, which stores a lot of energy in the progressive air spring, and gets unleased in G-outs (such as riding through a ditch while seated), and the deepstroke rebound (handled by a shimstack) cannot dissipate this energy.

So I upgraded to a H/H tune by replacing the compressionpiston in the Monarch. This improved the ride enormously, allowing me to open the rebound knob a little for softness in the top-of-the-stroke. But still it is not enough.

My next experiment will be to further tune the rebound shimstack of the Monarch. I'm also considering a Debonair aircan upgrade.

I'm very curious about your experiences

[pyre]

I have been riding a medium/medium tune Monarch for the past year and have resorted to extreme settings too.  I am it 250 psi to keep it around a 30% sag and to help prevent bottoming out but the small stuff tends to bounce me around.  I was planning on converting to a high tune this winter.

What PSI did you run with your medium tune and what are you running now with the high tune?

[two-one]

Hi, the tune will not change the springcurve, so if you need 250 psi, then that will remain the same. The compression tune only changes the firmness of the damping, so less comfort, but more platform to push against during pedalling or jumping.
What this bike definitely needs is een very very strong rebound tune, because the deepstroke compression ratio is more than 3.
Tonight im going to change my tune for a selfdesigned superhigh rebound tune, so hopefully I can open up the rebound control for starting stroke plushness.

[xcbarny]

Sounds like you should try the Debonair can to make your spring rate more linear, I think that is the bigger issue for you rather than rebound - how does the bike perform over small stutter bumps?

Apparently the Monarchs also come with volume reducer bands, similar to the travel tokens in the forks, that you can add or take away to tune the spring rate. On my duelly, I don't get full travel at my preferred sag pressure, so I was thinking of removing some of these bands to make the spring rate more linear. Not sure what year they started adding the bands though?

http://www.mbr.co.uk/how-to-2/tech-advice/five-minute-tune-rockshox-monarch-shock-324308

Although in your extreme case, I thing the debonair is the way to go.

[two-one]

Sounds like you should try the Debonair can to make your spring rate more linear, I think that is the bigger issue for you rather than rebound - how does the bike perform over small stutter bumps?

The leverage ratio of the FM036 is falling rate, so you actually need the progressive spring of a small air can to compensate for this design choice, otherwise you will actually bottom your suspension FASTER with the same sag setting.

Apparently the Monarchs also come with volume reducer bands, similar to the travel tokens in the forks, that you can add or take away to tune the spring rate. On my duelly, I don't get full travel at my preferred sag pressure, so I was thinking of removing some of these bands to make the spring rate more linear. Not sure what year they started adding the bands though?

These rubber bands are only available in HV and debonair aircans. For the 165x38mm shocks, the HV has never been made available, but the debonair can now be bought for this shock size.
I'm still convinced that the FM036 needs very stiff rebound tuning for improved plushness. I havent been able to tune it yesterday, but maybe this evening...

[xcbarny]

Ok, I took what you said about there being a big kickback, to imply that the spring curve was too progessive, and the shock was rebounding so fast that the damper could not cope with it.

However, if bottoming out is a big issues, then this mustn't be the case. In my head these 2 things are the opposite of each other.

In the comments section of that linkage design page you linked to, he says that Scott are using a low volume shock on the Spark, to counteract the falling rate linkage design. This seems to make sense to me, I'm just not sure where your big kickback is coming from. Maybe the shock is bottoming out hard, and that's what is causing the kick back?

Sounds like you need to reduce the shock volume, to match the falling rate of the linkage, as you said. Is there any way you can reduce the volume of the shock?

[two-one]

However, if bottoming out is a big issues, then this mustn't be the case. In my head these 2 things are the opposite of each other.

Bottoming the shock isn't my problem, but maybe @pyre had a problem with that.

In the comments section of that linkage design page you linked to, he says that Scott are using a low volume shock on the Spark, to counteract the falling rate linkage design. This seems to make sense to me, I'm just not sure where your big kickback is coming from. Maybe the shock is bottoming out hard, and that's what is causing the kick back?

Sounds like you need to reduce the shock volume, to match the falling rate of the linkage, as you said. Is there any way you can reduce the volume of the shock?

I'm actually happy with the progressive spring of the small air can (non-debonair). But the progressive linkage does store a lot of energy in the air spring. So when you use a lot of travel, it will return with a lot of force.

The rebound circuit consists of two channels: The adjuster (LSR or startingstroke rebound), and a shimstack that is tune-specific (HSR or endingstroke rebound)
So when the shock rebounds with as much force as it does, then the normal High rebound tune cannot slow it down enough.

To compensate I had to close the LSR almost all the way, but then the smaller bumps become much harsher (because the shimstack is closed for those smaller hits).