This post will likely mean nothing to you if you have yet to get out and do any serious trail riding on fix. Conversely, if you have done some fixing on trails, I apologize in advance for the PTTFSS [post-traumatic trail-fixing stress-syndrome] this may invoke.
Recent therapy sessions have allowed me to remember more clearly what happened in June ‘05 when I was fixing on some new crazy downhill in Morrisville, VT. [often known as Mo'Vegas---the place I went over the bars and landed on my original Vulture S/S, crushing the main frame tubes and putting an end to a great 5 1/2 year partnership] I had just got off and walked down and around a big steep rock slab of a drop in. It was totally an easy clean on a coaster, but a WAY SCARY skid-to-pedal-at-the-tranny-or-die type of challenge for the fix. At 20 plus feet in length, pedaling all the way down it would surely have put you at serious risk in the tranny….So, I had just walked down and around this and we were back on and tearing down this great trail [thanks, Ralph] when we came to a stair-step section. Feeling a bit resentful about the last walk-down, I looked this one over quickly, without stopping Very steep, but not so steep that behind-the-seat antics would be required. I didn’t hesitate and started in. With a bit too much entry speed, I realized about half way down that the last couple steps were at least half-wheel height. I got spooked. Of course, half way in and at a good clip, bailing was likely more dangerous than to keep going, so I decided to skid the second to last step drop, then pedal off the bottom one. This is the part I remember now….I skid dropped the penultimate step okay, but had too much speed still and got indecisive about that last one. This is where the dreaded Pogo effect is triggered. Keep in mind this analysis is highly theoretical and unproven. So, my theory goes that when you leg-lock, as opposed to braking [rim or disk] you are forced to move your center of gravity back towards the rear axle to maintain enough traction on the rear wheel to actually slow down. When you decide to release, you are naturally moving your center forward. Unlike braking, this causes the stored energy in your legs from your leg-lock to be released back into the drive/braking system with a force vector that is more perpedicular to the ground than parallel. Combine this with your body’s move forward and you get an over-the-bars-pilot-eject type of thing going on. Hence, when I went from leg-lock back to pedaling on the last step, the rear wheel pogoed from the energy transfer kicking the rear wheel up and me into the air. And did I ever go into the air. What I do remember about this part was that urgent effort to un-clip that comes with going over the bars…..then I remember the eternity of waiting to hit the ground. I must have gone fairly high, because it seemed like it took forever to come down. When I did, of course, I walked away without a scratch….and a completely pretzelled frame.
OK, I guess it was August ‘05: HERE’S A LINK TO THE OLD STORY AND SAD PICTURE
So…besides re-airing this laundry for therapeutic reasons, my point is that while trail fixing this summer on my new Vulture, I’ve learned to identify the Pogo effect and sadly, have been bailing on trying to ride downhills that put me at risk for the Pogo-Fix-Eject. I’m just too old for the over-the-bars-another-collarbone-bites-the-dust-stuff. For better or worse, we’ve got a term for this effect. And I haven’t been over the bars for a while, certainly not from pogoing.
I’m wondering if some of stored energy in leg-locking gets stored in the chainstays. I theorize that the loads created in the chain are “compressing” the stays during leg-braking. The effect of releasing the leg-lock “expands” the stays. The expansion of the stays kicks the rear wheel upward. Thus, the rear-end kicks up and sometimes you go flying. [engineers: your feedback on this idea would be appreciated]
So, I’ve been doing a fair amount of —- god, it’s true —– road riding. After just being a fat-deskjob-slacker for two years, I’ve been working hard to get to a new level of fitness. For that end, road riding avoids having to use a car to do a ride—-and as we mostly know, it’s great training for trail and single-speed riding. Just did a great VT road [with a little dirt] ride from Williston to Waterbury yesterday. Only about 35 miles, but a nice way to start the day.
One sad note. Over the years I’ve gotten in the habit of looking over my bikes a bit before a ride….just a bit paranoid, but this story will pan out. So, I’m looking over the GX, which is about as close to a road bike as I’ll likely ever own again. I found that the really crappy powdercoat I got on this bike was showing little rust blisters all over it. I got nervous. I did a much closer inspection and found some scary stuff on the bottom of the chainstays. Short story: VT corrosion has rotted through the powdercoat and just made itself at home inside the stays. There is actually a small rust-through hole. I fear now that acid rain got inside the stays and never evaporated out…so it just corroded its way out. I think the GX may be done. [insert weeping here] I’ll be seeing and talking with Wade later this summer, but based on my inspection yesterday, my road riding is on hold ’til further notice. I have no way of knowing how bad the damage is. I think probably a sandblasting a return to the maker for further evaluation is the only option. Sheeyit.
All else is well in my world.
Stay tuned for more trail fix feedback. Keep in mind I am still in the learning phase of my new job, so I don’t know I’ll be able to post to often this summer.
Thanks for reading.
Over and Out.
G:5