Sunday, September 21, 2008

Back to the Trance

I got to take theTrance out again today. We went to The Newlight Trails A great mixture of fun and tough. Lots of short rooted climbs for an old man(That would be me) to tackle and I am clapped out(Not a reference to an STD). So this, the Trance story, may run to a three parter.
Back to setting up the suspension. I know this is not specific to the Trance, but I get asked a lot about doing set up so this seemed as good a time as any to include it, and it applies to all suspension setup. Yesterday I talked about setting sag and setting rebound. Today we will go into compression damping.

By the way the controlled action of the suspension is damping, not dampening. Dampening happens when you wash your bike. And quit putting a "U" in stanchion. One more, don't pout when you find out you cannot pump up your shock with a floor pump.

Back to compression. This is the controlled motion of fork in the compressing (when you hit a bump) direction. Most forks/shocks do not have adjustable compression. If you are one of the lucky few, you want to set it up so that the fork/shock reaches full compression on the hardest thing you hit. This makes set up easy for a course but harder for general riding. However, most people ride in the same places all the time so you should have a good idea of where the big boys are. I wish that more suspension had this adjustment because, if you are fully compressing the fork, often the only fix is to increase the preload(More air or bigger spring). Even upping the weight of fork oil does not help much(It is good if you need to increase rebound more than the adjustment allows) The big problem with increasing spring rate to solve a compression problem is that it reduces your sag. You don't want to reduce sag much because this is what helps keep the wheel planted. The suspension needs to be compressed a little so when you go over a hole or other drop the wheel can quickly move into it and retain grip. This also reduces the jarring on the rider.
In the case of the shock on this bike, a Fox Float RP23, there is also a Propedal lever with three settings. What this does is increase the initial compression damping. This helps when you ride mixed trail with rough and smooth sections. You can get out of the saddle and sprint with minimal rear suspension movement but when you hit a big root or rock it will move past this high damping and into the normal rate. The three settings let you pick just how hard a hit it takes to get out of Propedal. The fork, a Fox 32 F120RL, has a similar feature with its lock out, but there is only one setting.

So, I set my bike up based on my 180 pound weight(I am trying to correct this by growing another two inches, which reminds me of a Richard Pryor joke) 90psi in the fork and 180psi in the shock. A sag check showed me in the ballpark. I dropped the pressure in the shock to increase sag a touch(This later proved to be a mistake as stiction was screwing up the sag a bit) Then I increased the air pressure a little in the fork. This also was a little bit of a problem but I had test ridden down a stair case and it felt to soft(Have you been paying attention? How would I fix this? That is right more compression damping, however that knob is missing from this bike) Turns out this made the fork a little to stiff and the sensation I was feeling, being tossed over the bars, was better alleviated by increasing the rebound on the shock. This slowed the rear down so it did not feel so much like it was catapulting me. Unfortunately I did not get to play with the pressure for the actual ride as my pump was resting securely in the tool box, where it could not be stolen(or used).
Alright, I have to call it it a night and fall out before I fall down. To paraphrase Bullwinkle, "Tomorrow, for sure"

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