Gearing versus tyres-
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  1. #1
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    Reputation: Velobike's Avatar
    Join Date
    Jun 2007

    Gearing versus tyres

    I usually run a 32/20 on my 29ers in reasonably mountainous country (Highlands, Scotland).

    I've got a 12 hour race coming up so I arranged to go out for some practise on the track. It has some long gravel fireroad climbs, plenty varied singletrack, and the usual you can hurt/scare yourself here technical stuff.

    When I went to go, I noticed my 29er had a flat, so to avoid delay, I grabbed my nearest bike - my drop bar cross bike which is a 47/18 and 37mm tyres.

    What amazed me was that I felt much faster on most of the hills and in some cases I was getting beyond my usual get off, walk, and gasp points. On the rolling stuff I had a ball - piece of cake. There wasn't much flat but naturally that was good too.

    I was hopeless on the technical stuff - too scaredy cat for riding down steep stuff with a head down attitude and canti brakes, but I expected that, and I've never been great on it anyway.

    My 29er is 9.5kg, which is about the same as the cross bike, so the important variables are drop bars v flat, tyre sections 2.35 v 37mm, and gearing 32/20 v 47/18.

    Basically, the road bike feels much faster even on the climbs. It feels like hard work because of the high gearing but there was very little I couldn't climb with a bit of body english. It felt really natural to me because all my early offroad riding was done on drop bar road bikes.

    I'm now thinking of sticking flat bars and v-brakes on it and racing it instead of the 29er and run on the tech stuff.
    As little bike as possible, as silent as possible.
    Latitude: 5736' Highlands, Scotland

  2. #2
    mtbr member
    Join Date
    Apr 2009
    Heh... yeah, I have a similar experience. I bought a Spec TriCross a year or so ago with the intention of doing some long distance road riding / touring. On a whim, I decided to take it to the trails instead of my mtb, and I was rather surprised at how well it handled just about everything (except the really techy stuff, as you noted). That was a great bike, but I ended up selling it b/c a new baby does not give much time for touring or extended riding. Since then, I've seen a couple of these outfitted with mtb bars and converted to SS for ripping up the XC trails.

    I think the majority of the differences you are talking about (better climbing, faster with less effort, etc) come from the more efficient riding position. And it is the position you trained in, so it is going to feel natural and powerful.

    Sure, the narrow tires offer less resistance (but also reduced traction)... and the taller gearing is just going to _feel_ faster even if you have to crank on it. I don't think there's really enough difference between a moderately sized 29er tire and a 700cx37mm to make up for the difference in gearing.

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