# Leverage Ratios and Monarch RT3 on Motobecane Fantom Pro DS

• 10-08-2012
Koin
Leverage Ratios and Monarch RT3 on Motobecane Fantom Pro DS
I have posted this same thread in the shocks and suspension section of the forum as I think that section more suits this thread. Here's a link http://forums.mtbr.com/shocks-suspen...ml#post9761985

Hello everyone. So I've been having some problems with my rear shock. It's a 2012 Rock Shox Monarch RT3. Despite all of the good reviews, I could never get the shock set to proper sag for my weight.

The shock is a 2012 (I think) Rock Shox RT3
165x38
Says ML (M in blue box and L in red box)

My bike frame is a 2010 Motobecane Fantom Pro DS
I weigh 190lbs

I've been searching around the forums and found some articles all about the monarch and leverage ratios etc. Someone once told me that the Fantom DS frame has a leverage ratio of 3.33:1 in the 5in travel setting. What are the leverage ratios for the 4in and 3in settings? How can I calculate this? How do I interpret the chart in this article in the first place? I also don't know the equivalent ABCD tune for my shock as it only says ML

http://forums.mtbr.com/specialized/2...ro-666525.html

Somewhere I read that leverage ratio is calculated by taking the travel over shock travel. If that's the case. then I presume that I need to convert the inches to mm. However, if I take 5in and convert to mm I get 127, then 127/165 does not equal 3.33. So I'm doing something wrong there.

Anyways, so that's me trying to think about things outloud. My problem is that I have to top the shock out at 250-260psi (I always tend to lose psi when I disconnect the shock pump) to even get 30-35% sag in both the 5in and 4in travel settings. That doesn't seem right as the shock is rated to only go to 275psi. I would guess that I have a low tune shock and need a medium tune shock. I just wanted to know all about the leverage ratios and what not so I could prove it to myself.

Is there any way to tune the shock using the IFP pressure to suit my weight? I found a nice article all about that, but I really don't know much about the whole theory behind IFP. http://forums.mtbr.com/shocks-suspen...ge-524727.html

Do I need a new shock? In the 3in travel setting I can get 25% sag with about 190psi. I want to run in the 5in travel since I tend to like jumping off stuff. If my frame can allow more travel why not right? If not 5in travel at least 4in.

Thanks.

The attached photo is of the shock in the 3in travel setting. the shock is current flipped upside down and in the 5in travel setting.
• 10-23-2012
m_dub007
I am having a similar issue of needing to pump the shock up to ~250 to get a decent sag %... did you figure anything out??
• 12-30-2012
lvstrshygrls
i have a phantom comp ds and experience the same problem in the 5in travel setting with a fox float and am convinced an air shock can't produce a heavy enough spring rate to handle the leverage issue you speak of
• 12-30-2012
Koin
Yes, I did figure something out. After talking to the guys at the lbs, it seems that, like lvstrshygrls said, the shock can't withstand the high leverage. After looking at some of Rock Shox's tuning guides, it seems that for this frame a high tune shock would be desirable for the higher leverage ratio. One could rebuild an existing shock and just purchase a high tune piston, a shock rebuild kit, and shock oil for around \$80. I might go this route, I'll have my lbs help out of course. Rock Shox provides service manuals on their website that shows step by step rebuild of the Monarch RT3 and other models, they also have a video on youtube which shows the steps as well.

I'll be trying it out once I have more disposable income. Hope that helps you guys!
• 01-29-2013
ProfGumby
An especially interesting topic to a Clyde like me. I am positive the rear shock will be the weakest link in ANY fs bike I buy....