Sunday, May 30, 2010

Tubeless for Cyclocross

I had been wanting to try it for a while, so I finally got the Stan's NoTubes Cyclocross kit and gave it a try. My first thought was to try the conversion with one wheel from each wheelset and test them out to see which worked the best. I started with a Mavic Aksium wheel and a Vittoria XG Pro tire. With a liberal sudsing of soapy water, I got the combo to inflate with my floor pump. It helped to hold the tire in a certain way, I pulled the sidewalls apart as far as I could so the tread was laying flat and held it against the rim with my palm while I supported the wheel in my hand. Easier to do then to describe.

It worked so well I decided to skip even trying the Kysrium Elites or Mavic Reflex clinchers. Besides, I didn't really want to subject the Elites to cyclocross, and I had heard that OpenPro (similar to Reflex clincher) was a poor candidate for tubeless because of the deep center channel.

I then added sealant, and had both wheels converted within an hour. Over the next two days, I went on several rides while successively letting air out to lower the pressure. I started with 40 psi and got down to 20 psi in the front, and 25 psi in the rear with no signs of burping or air loss. Not much point in going lower, or I'll just be riding on the rims. So far so good!

Next, I need to find some fast, flat, grippy east coast grass to really put the side loads on, but I'm feeling confident that this will make a great racing combination so far. 20 psi in the front, and 25 psi in the rear is much lower then I could run with tubes, I can feel the difference as I float over rocks and roots instead of bouncing around.

It's only the end of May, and I'm getting excited for cyclocross season already.

This bike came with the usual chainrings for a compact crank on road (50/34) and the 50 was just about useless on most courses, at least for me. I swapped it for a TA Specialties Zephyr 9/10 sp 42 tooth outer ring (ramped and pinned, nice!) which is infinitely more useful on a cross course. I'm hoping I'll be able to ride it like a single chainring configuration, and not have to shift the front during a race.

I also switched the rear derailleur from Ultegra to Shimano XT (MTB) in order to accommodate the IRD 11-34 10sp cassette for Becca. It was very fortuitous that I grabbed the medium cage version ($5 at the Velodrome flea market) instead of the long cage version that I thought I would need. It turns out that because I changed the big chain ring from a 50 to a 42, that reduced the number of chain links that the rear derailleur needs to take up to a number that is within the capabilities of the medium cage.

Shimano long = 45T; medium = 33T

(42-34) + (34-11) = 31T

Perfect. Now I can leave the 11-34 on the bike with road wheels for Becca, and swap to the cyclocross wheels with a 12-25 and not have to worry about chainlengths or anything else.

The last thing that I did was to get rid of the front brake cable hanger that mounted with the spacers on the steerer tube. It was really close to the stem and put a sharp bend in the cable. Although the bike didn't have any brake shudder problems, the fork seemed like a better place for the cable hanger. (See Leonard Zinn on brake shudder)

Thanks to Cutters bike shop for drilling and tapping the Tektro hanger for a threaded cable stop.

The bike is ready, and I'm ready, when does cyclocross season start?

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