Shock Tuning

gtd.

I have a Rock Shox Monarch 3.3 190mm i2i 50mm stroke in D3 tune on my Patriot

I don't understand the rising/flat and falling rate bit but ...

http://foto.mtb-forum.it/data//950/tune.jpg


I'm using the 6" travel mounts on the frame and swing arm and to fit the shock this way I have to fit it so the air can is pushed over the shaft, rather than pushing the shaft into the air can.

Is this ok?

If I'm using 6" travel mounts the swing arm has a leverage ratio of 3 ( 152.4mm / 50mm =3) which on the chart above looks well out of spec for the shock as it looks like it works best with a leverage ratio of 2.2-2.3

I weigh around 17 stone and have to run the shock at 270psi to get the 30% sag (max pressure stated on shock is 275 psi)

The bike also has 5" travel mounts giving a leverage ratio of 2.54 (127mm / 50mm = 2.54)

Still out of spec but not as far...

Is it possible to change the tune of the shock myself? (adding air to the nitrogen port?)
or is it a shim stack job?

or should I send it away?
or should I just buy a Monarch Plus RC2 in the correct tune?

nicklouse

the rate the shock is compressed in relation to the "travel" bikes rarely have linear rates of compression the rate either rises or falls.

gtd.

I've changed it to 5" and turned it round.

It now is about 20-25% sag and the three position compression gate seems to work better :?

nicklouse

you are on the right path. to get more travel out a shock you have to increase the ratio which means more work and higher spring rates. reducing the travel by changing the mounts changes the leverage ratio with reduces the spring needed. If that is the Max pressure you may need a different shock (fox are ok to 300IIRC) but again 30% on a 6" travel frame is not bad.

back to Rates. air forks/shocks are rising rate. (that is what happens to air as it is compressed. the spring rate increases following a parabolic curve.) this also effects closed spring forks and air assist preload forks. a steel/ti spring when compressed in a straight line is a liner spring.

But what you then have to consider is the suspension designs rate. any design pivoting about a static point will have a changing rate. this can be worked into the shock design to effect how things work. A rising rate sus design with a linear spring with give a rate as per the suspension. a Falling rate Design with a rising rate spring may give a linear suspension feel ( Whyte/Marin) a rising rate with a rising rate can be odd or great.

But that is the springs. the damping also has lots to do. on a linear set up it can do the same all the time. with a sizing and falling design it has more to do at one end or the other of the stroke. this is more a suspension design issue as damping is a movement issue rather than a force. (sorry tying to keep it simple).