living the dream

June 2008
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twenty nine
Filed under: General
Posted by: Todd @ 3:45 pm

Or, to be specific, 29.0075475. I’m talking about PSI, not inches… More to the point, I’m talking about two Bar.

It was like any other Fells ride yesterday, save for one very important detail; my tire pressure was perfect.

I’ve been playing around with inflation to find the right combination of traction, flotation, cushion, and speed. On a fully rigid singlespeed, this can be a difficult combination to get right, but I think I finally did. After weeks of fumbling about, aiming the needle of my pump gauge “a little past this line” or “just shy of that one”, all with pretty okay results, I thought out loud, “Why not 2 Bar?”

Bar, for those who don’t know is a unit of air pressure based on atmospheric pressure at sea-level. The short of it is one Bar equals one atmosphere (at sea-level), which equals 14.5(ad nauseam) PSI.

By coincidence, my Michelin Mountain AT, 26×2.3 tires on MAVIC Crossmax ST wheels under my 190~ish pound self work really well at two Bar. The beauty of this is that two Bar is neatly marked on my gauge, where 29.0075475 PSI is not.

Maybe it’s too much for some of you to stomach; I’ll freely admit that I geek out about tire pressure almost as much as ThomP does about gearing. Still, something magical happened on that trail yesterday that I can only attribute to two Bar. The rock gardens felt smoothed out, steering on the singletrack felt precise, there was grip to be had on mud-slicked rocks, the fire trails felt fast and tight, and I felt my rim bottom exactly once (It is said that if you don’t bottom your suspension at least once per ride, it’s too firm and you’re not using all of your travel… The same can be said for your tires). On my 20-inch, I run 70 PSI in the rear and 65 in front. On my road bike, I ride 110. Now, finally, I can say I’ve discovered the magic number for the mountain bike (Sorry, Posdnuos, P.A. Mase, and Trugoy… it’s not three).

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