Monday, February 13, 2012

Winter Bike Projects

The saying "if it ain't broke, don't fix it" holds true in many situations. However, I am a scientist and I like to tinker with stuff to see if my ideas would improve things, or just because I am curious to see what happens. In science experiments, the success rate is really low, perhaps 10%. In technology and engineering, such as bicycles, I tend to believe success rate must be higher, because smart people have figured it out already. But if they really did, wouldn't the saying above always apply?
So the changes I did to three of our bikes described below may seem like unnecessary, but they have a certain logic which I will try to explain.

Part I: Mojo 2x9
Of course, we all know that the new Shimano and SRAM 2x10 drivetrains are all the rage these days. Interestingly, the mainstream technology spurs ideas like a 1x9 or 1x10, all based on the question: "how many gears do we really need on mountain bikes?". I know, some people would say "just one", I have been through that phase before....
I asked myself this question: how many gears of my standard 3x9 setup (11-32 cassette and 22/32/44 triple) do I really use? Riding around the Bay Area on some really steep hills both up and down, one would think I used the full range. In reality, it is more like this: on steep climbs, I tend to ride 22/32 or 22/30, then shift to 32/30 - 28 etc. as the terrain becomes more rolling. In the middle chain ring, I tend to use the low gear half of the cassette. When spinning out on downhills, I shift the 44 chainring way before reaching the tall gears just because it is way fewer shifts and the chain bounces less at 44.
So using the Bike Gears iPhone app, I figured that changing to a 2x9 setup, using an 11-34 cassette and 24+38 chainrings would yield gear range quite close to what I have now. The lowest gear would be tiny harder (1.373m of development vs 1.337m) and I would lose more at the high end (6.719m vs 7.780m), but then how often does one ride at 44/11?
Here is the solution:
  • SRAM PG980 9-speed (11-34) cassette
  • SRAM X-9 long cage derailleur

  • Shimano XT cranks
  • Blackspire 24 and 38T chainrings mounted to 64mm BCD position (24T) and the middle        104mm position (38T)
  • Shimano XT front derailleur locked by the limit screw in the middle position
  • SRAM PC-991 chain
OK, so everything is in place, it shifts beautifully on the work stand and in the parking lot test. The next test, of course, will be climbing and descending on trails. Stay tuned for a ride report.

So this takes me to the Part II of the project: Marketa's Specialized Myka Expert bike is really heavy for a women's bike. What makes the Specialized product managers think women need bikes heavier than guys'? So one way to make it lighter (after researching some of its components weights online) would be to swap the Alivio crankset / front derailleur and the cassette for XT-grade components. See? If I really like my 2x9 setup on the Mojo, the next logical upgrade would be going full 2x10 SRAM X0, thus all the 9-speed components from the Mojo would end up on the Myka.
But the best place to start saving weight is wheels and tires. That's where the 3rd bike (my Motobecane Phantom Pro 29er) comes into play. This bike comes equipped with pretty lightweight Vuelta XRP SL wheelset and I have been using Kenda SB8 tires pumped up to 50psi for commuting to work on pavement. These tires perform really well on dry dirt in loose and dusty conditions and have a low rolling resistance. Front wheel with tire, skewer and a large 180mm rotor weighs 1800g:

The Myka uses Specialized own Stout hubs laced to some Alex sturdy looking rims, but with nicely color coordinated green anodized spoke nipples. With Specialized Captain Control 29x2.0 2Bliss ready tires it weighed 2150g:

 OK, so I was not ready to swap the whole wheels just yet, but thought that swapping the tires would give the Myka an advantage of ~ 200 grams less and lots less rolling resistance. My 29er would be OK with heavier tires - I will just pedal harder on my commutes and have more tire tread for wet trails in the winter.

As you see above, the Vuelta+Captain combo comes out at ~ 1875g and the Specialized+Kenda combo at 2000g. Given the +/- 100g accuracy of the scale, looks like about 200 grams (both front and rear) moved from the Myka to the Motobecane, as predicted based on published tire weights.
But the real test would be in real world conditions. First chance to test the 29er "new" tires presented itself the very next day.

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