Gear: February 2009 Archives


February 15, 2009

Usually I do my long runs at Rancho San Antonio (PG&E Trail or Black Mountain) but the past few weeks it's been incredibly crowded to the point that I had to park on the road leading up to the park and then run in. I thought it might be worth changing things up so this weekend I tried a different route, the Alambique Trail in Wunderlich County Park. At the entrance to the park is a free dirt parking lot with a portajohn. From there the trail goes from about 400 feet 5.5 miles up to Skyline (this is with the Skyline trail at the top rather than the Alambique trail all the way). It's basically one continuous climb to the top and then you turn around and come back down (there are also extensions along the Skyline Ridge Trail to Huddart park.) The trail is quite well marked--there was one place where I got off course because I saw a path that was well trodden but unmarked. Should have stuck to the signs.

Compared to Rancho, the footing is generally worse, with a lot more foliage, rocks and roots, as well as a fair amount of horse manure you have to dodge. The trail is a pretty good workout, but I don't really like the up then down format. The climb to the top is unrelenting and then you really pound your quads and your knees coming down that 5 mile descent. The PG&E Trail, for instance has about the same amount of climbing and even some long up or down stretches, but a fair amount of it is rolling. Today it was raining (pouring, really) and while footing was good, thanks to my Inov-8 Roclite 295s, a significant fraction of the trail was puddles, streams, and mud, with the results you see above. This actually understates the situation a bit, since I'm wearing green socks and so you can't see that my shoes and socks are covered in dirt, leaves, sticks, etc.


February 14, 2009

OK, this is incredibly cool: Shimano has what looks like a viable electronic shifting system. Most people don't think a lot about bicycle shifting, but this a topic of real interest to people who do a lot of riding: mechanical shifting kind of sucks and a working electronic shifting system would be quite nice.

As background, the way bicycle gearing works is this: on the front you have either two or three gears ("chainrings") directly connected to the pedals ("cranks"). On the back, you have between 5 (if your bike is ancient) and 10 (if your bike is new and expensive) gears. They're connected to the rear wheel by a ratchet so that when you pedal faster than the wheel, it drives the wheel but if you stop pedalling while you're riding the gears spin freely with respect to the wheel so you can coast (this is called a "freewheel" or "freehub" depending on how it's put together.). The gears are connected with a chain. Anyway, the amount of mechanical advantage you get is determined by the ratio between the front and back gears. If they're the same size then every turn of the pedals turns the wheel once: the bigger the front gear the harder it is to pedal (but the faster you go with each pedal stroke); the smaller the front gear, the easier it is to pedal but the slower you go. The opposite is true for the gears on the back.

Roughly speaking people choose the general range of the gearing with the front gear and the fine-grained gear selection with the back gears, which are closely spaced. So, for instance, if you want to climb a hill you'd choose the small gear in the front. On the other hand if you're on flats or the downhill you would choose the big ring. Incidentally, while it's natural to think of the gearing as being sequential, it's not. Let's denote a given gear configuration X-Y as being ring X on the front and Y on the back, with "harder" numbers bigger. So, 1-1 is the easiest gear and 2-10 is the hardest. However, 1-10 is almost always harder than 2-11 and there's actually quite a bit of overlap. This means that you can get a fair amount of gear flexibility without changing the front gear, which is good because front gear shifts are very clumsy compared to back gear shift.

Why Electronic Shifting Is Promising
Mechanical shifting has a number of drawbacks, mostly connected with the front derailler (the gizmo that does the shifting):

  • Because all the linkages are mechanical you can only really have one set of shifters. This is inconvenient for triathletes and time trialists who tend to use aerodynamic handlebars a lot of the time. You can put the levers so you can shift conveniently in the aerodynamic position or the upright position but not both.
  • The front derailler doesn't shift well under load, so if you suddenly find yourself on an uphill (which means you're putting a lot of load on the chain) it can be hard to downshift, which is inconvenient because this is exactly when you need to shift. In the worst case, the chain can come off and then you're really hosed.
  • Because the rear has a lot of gears stacked on top of each other, there's a lot of displacement of the chain even as far as the front. This means that you need to "trim" the front derailler to stop it from rubbing; a configuration at the front that works with the biggest gear in the back will cause rubbing with the smallest gear in the back and vice versa.

It's easy to see how electronic shifting can solve the first of these: you can run as many wires as you want so you can have shifters in any location you want. This has been obvious for quite some time and there have been a number of stabs at electronic shifting but they've never worked well. Early reviews suggest that Shimano's does.

Another advantage of Shimano's system is that the front derailler is self-adjusting: this means that you don't have to trim and that allegedly it shifts well under load. The downside is that it's $4k for now, but this is the kind of thing that comes down in price.

1 Technical note: gears are denominated in the number of teeth. For instance, a 20-speed bike might have two front chainrings with 53 and 39 teeth, and 10 back cogs with teeth ranging from 11 to 25 teeth. With our above notation: the ratio for 1-10 is 3.5 and the ratio for 2-1 is 2.12, so there's a very substantial amount of overlap.


February 8, 2009

Most climbing at climbing gyms is done on top-rope: this means that the climber is supported by a rope that runs through an anchor at the top of the wall. The person holding the other end of the rope (the belayer) stands at the bottom of the wall and takes in the slack in the rope as the climber ascends. I suppose it's theoretically possible to belay just by holding the rope in your hands, but it's prohibitively difficult: most people can't easily apply 150+ pounds (600+ Newtons) of force to a rope continuously, and if the climber is falling, it's much harder to stop them. Instead, you use a belay device: a gizmo that attaches to the belayer's harness and lets the belayer apply friction to the rope.

Most modern belay devices are of the "tube" variety, such as the ATC, shown below.

The way that an ATC works is that the climber's rope goes through both the ATC, which is just a metal tube, and a carabiner attached to the climber's harness. In order for the climber's rope to pay out, it has to feed through the carabiner and the ATC. To stop the rope from feeding, the belayer pulls on the free end of the rope with his brake hand, which pulls the rope tight against the edge of the ATC where friction stops it. Effectively, then, the climber is hanging from the belayer's harness (remember, the rope is going through an anchor above the climber), with the belay device coupling the rope to the carabiner.

The key point here is that an ATC is passive; if you ever let go of the free end of the rope, it will feed freely and if the climber is weighting the rope, they will fall, potentially to their death. This makes technique important. In particular, as the climber ascends you need to take out slack in the rope by pulling on the free end. However, eventually your arm will be fully extended and you need to move your brake hand up the rope. It's important to do this without letting go, because if the climber falls during that period there's nothing to stop them. The standard technique for this is to take your other hand and grab the rope below your brake hand and then slide it up, so there is always a hand arresting the rope. There are other techniques, but they are less safe.

You can also get active belay devices which autolock if tension is suddenly applied. The most popular of these is probably the Petzl Grigri. The Grigri has two main advantages for toproping: first, if you're not paying attention and the climber falls, the grigri will autolock and catch them [there is a lever you pull to unlock the device so the climber can descend.] Second, if the climber needs to hang for a while, you don't need to apply tension to the free end of the rope to keep it from feeding through as you would with an ATC. [Lead climbing, where the climber pulls the rope up with them and sets their own anchors, is more complicated. Here, I'm just talking about toproping. Grigris are popular in part because the autolock seems safer. Planet Granite, where I climb, has Grigris fixed to the line and won't even let you toprope with an ATC. PG also has another safety feature: the anchors at the top of the wall are large diameter (4-6") metal pipes with the rope wrapped around the pipe twice.. The effect is that when tension is applied to the rope it cinches around the pipe, creating a lot of friction and thus arresting the climber's fall (though not necessarily to the point where they couldn't get hurt) even if the belayer does nothing. [Technical note: the instructors at PG regularly tell students that the double wrap halves the climber's effective weight, but this misunderstands the basic physics. There's no movable pulley; it's purely a friction effect.]

I'm not sure that either of these are really good ideas for a climbing gym. While I suspect that Grigris really are safer for topropoing if that's all you use, they don't give you any feedback for bad technique because the climber won't fall even if you totally fail to lock off the device yourself. It's quite common to see people using the "pinch" technique where they pull the free end of the rope up to the end going towards the climber, pinch them both together with their free hand [which is usually pulling down on the rope to feed it through the aforementioned high friction anchors], and then move their brake hand up towards the belay device. This is OK with a Grigri, but because the ATC's friction depends on the rope being pulled against the edge, doesn't provide acceptable braking with an ATC. Yesterday, I heard an instructor at PG tell a belay class that if they lost control of the climber's descent (e.g., you're pulling the lever and having trouble braking with the brake hand) you can just let go and the Grigri will autolock. While this is true with a Grigri (though you're not supposed to rely on it), it would be disastrous if you were using an ATC. So, my concern here is that always using a Grigri encourages bad habits that could get you into real trouble if you ever used an ATC, either because you were lead belaying or were at a gym that had ATCs instead of Grigris. Perhaps what would be best would be if some small fraction of the ropes at PG were set up without belay devices and they encouraged you to use ATCs on those so you would learn how.

The pipe thing is even worse. Lots of gyms have anchors with much lower friction (e.g., carabiners at the top). If you're used to the slow descent provided by the pipe, you could drop your climber way too fast even if you were using a Grigri. Even if you don't ever climb at another gym, the variation in anchor friction is quite high with the anchor getting slower as the rope ages. I've seen anchors where the climber actually had to bounce to feed the rope through and descend and ones where there was barely more friction than a carabiner. So, this is a problem even if you only climb at the same gym. Again, I know why they do it: it seems safer, but it teaches bad habits which could get you, or rather the person at the other end of the rope, seriously hurt.