Tuesday, March 29, 2011

When Less is More

In When 16 is Not So Sweet I admitted that I still run tubes while blogging about repairing a flat on a 29" mountain bike tire prior to a ride.  I have been getting grief about that fact for several years, but have been reluctant to try something new. Since that blog, the same tire has flatted 2 more times so I finally gave up on that tire.  Since I was changing tires, it seemed like a good time to explore the world of tubeless mountain bike tires.  The stated advantages of tubeless mountain bike tires include the ability to run lower pressure to improve traction without risking a pinch flat, and added sealant makes them self-sealing when punctured by sharp objects.

In this case, the rims were tubeless ready, but still needed a special rim strip and valve stem to seal the inner portion of the rim.  The next detail was picking-out tubeless tires which have to be installed in a special way.

The tubeless tires have a special bead with a soft rubber compound that seals the tire against the rim for an airtight fit.  You also need to put some sealant juice like Bontrager Super Juice or Stans to seal any small leaks or punctures while riding.  Getting them to pop in place takes some high pressure and good technique.  Tom showed me a neat trick of brushing water mixed with dish soap on the bead to lubricate it so it will not get hung on the rim when seating.  The bead on the tires will seat when there is sufficient pressure added and make a rather surprising and unnerving loud pop.

Both tires installed and seemed to hold air on the 1st try, so I was anxious to try them out on the commute home from downtown.  I am fortunate, that if I commute on a mountain bike that I can include the HD trails so about 1/2 is on road and 1/2 is on dirt trails.  I normally ran about 50 psi in my tires to minimize the chance of a pinch flat.  This helped for flats, but made the tires hard as rocks and quite bouncy every time I hit rocks and tree roots.  It also did not do a lot for my traction on loose terrain like sand or gravel.

I played with different pressures and finally decided on 35 psi for the rear and 30 psi for the front and headed south for the bluff.  The ride was surprising supple and the wider footprint of the tires seemed to hook-up better in areas I had spun-out previously.  So far, so good.

My next test was the 24 hour course out in Riverside State Park.  Same results as before, but I found that I could ride through the rock gardens faster because of the supple ride and better traction the lower pressure gives.  Everyone who rides that course knows it can be punishing to riders, bike and tires but the tires seemed no worse for it today.  I cannot attest to the self-sealing aspect of the liquid sealant in each tire since I don't know whether anything punctured them during the rides.  All I know is that I did not flat with less than 36 psi in each tire.

Bottom line - there seems to be something to this tubeless thing where less is more.  I will keep testing the limits of the technology to the extent my humble riding abilities will allow and report back in the future.

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