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October 11, 2009


Filed under: Riding and racing — mtbguru @ 11:03 pm

So far I’ve never quite experienced mechanical failure of catastrophic nature on the trail – good, I’ve had my share of flats, torn sidewalls, broken chains, vaporized brake pads, bent rotors, minor crash damage and a pretzeled wheel (but that was in college and there were two of us on the same bike). But today my lucky streak kind of ended.

The day after our onerous excursion in Coe, I found myself in south San Jose with some hours to spend before the sun would go down, and I was thinking – what better recovery ride from Coe than a nice short sunset ride in Coe? So I headed to Hunting Hollow with the Red Rocket (my Salsa) and had just started to pick up some speed on Coyote Creek road, as I experienced some trouble with the rear shifter; no worries, a few quick shifts up and down to jog the chain in place I thought but all of a sudden the chain locked up; this was accompanied by a loud crunching sound, after which my drivetrain halted driving anything… turns out half of the rear derailer cage had sheared off and disintegrated, due to what looked like some twig or stick getting caught up in the cassette and/or pulley wheel (and me greatly exceeding the force that one should put on the chain in such unfortunate conditions).

Derailer cage sheared off

Even worse, derailer parts had caught, scratched up and damaged a few spokes, and my Salsa derailer hanger thingie was bent beyond hope. Those spokes are made out of polyphenylene bensobisoxazole fibers (aka plastic wires), and I was impressed by how well they held up – the wheel was still perfectly true and certainly useable, but I didn’t care much for the only idea that could save my ride today: trying to make a temporary singlespeed out of my Salsa. Reasons for this: (a) this is Coe, the place is just not ment for singlespeeding, (b) I was only a few hundred yards from the parking lot, and (c) I didn’t have a chain tool with me.

Spoke damage

And thus was my sunset ‘ride’ over. After I’d completed the most pointless drive I’ve done in recent history and gotten back home, I decided to seek opportunity out of this unwanted change, and improve the bike’s bling a bit further: say hi to this Redwin Red cutie.

October 1, 2009

Pedal power

Filed under: Tech Corner — mtbguru @ 7:51 am

A power sensor has always been on my gadget wish list, as a bona fide bike geek should. However, the prohibitive cost of such things and their non-portability has always kept it in quarantine there. Portability may not matter to some but it does a lot to me as I’d love to experiment with singlespeed vs geared, 26 vs 29, road vs mtb etc -and swapping wheels or crankset doesn’t really work here. Of course, the main requirements are accuracy and consistency – this means so far I’ve been stuck with the – non-portable – crank or hub option. I could give the iBike the benefit of the doubt (a device that basically measures wind speed and inclination and hence the power demand, in order to estimate the power put in), but it just doesn’t cut it for me (it may be great in conjunction with a second power sensor on the bike though).

What would work well for me is a sensor that can be either mounted (a) in the shoe (b) on the cleat or (c) in the pedal. And which produces an accurate and consistent signal, of course. I’ve been thinking about this for a long time and was about to embed some piezoresistors in a shoe or cleat myself, but it now seems a very promising effort is underway – and close to market. In fact, a number of such approaches have been tried out or are being developed; the late Microsport Technologies tried a sensor integrated in a shoe, the Brimm Brothers are working on a cleat sensor, but the Metrigear Vector, presented at the latest Interbike, looks now to be the first one to launch. It seems to be based on silicon piezoresistors (which I always thought would be better than traditional strain gauges, since they’re more sensitive and you can more easily measure the different components of the force vector), in conjunction with an accelerometer to measure cadence/crank position (the latter is an absolute requirement for pedal/cleat/shoe based sensors), and is integrated in the spindle of the pedals. Bikes and MEMS, right in my backyard!

Metrigear is also a local (to me) startup, and led by a guy that climbs Kennedy in 30 minutes flat – though he used a crossbike ; ) – so they must be serious about their cycling! The device is ANT+ compatible, so it will work with e.g. a Garmin 705 as head unit, it will come initially as a modified set of Speedplay pedals (mainly for road) but is promised to become available in different types later. Dan Connelly (from low key hillclimb fame) is doing a nice job in discussing the device in more depth and there is lots of chatter and talk about this on the Wattage Google/usenet group. There are still many questions, about the battery, durability, sealing, signal processing and availability etc but I’m for sure hoping this works as well as advertized!