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Old 12-23-11, 05:55 PM
  #20  
cyccommute 
Mad bike riding scientist
 
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Join Date: Nov 2004
Location: Denver, CO
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After my experiences yesterday and today with rides on 10" of fresh snow (yesterday) and car packed snow today, I thought it might be illustrative to revisit the tire pressure issue. Yesterday, I left my house with the tires at the same pressure I use them for riding on dry pavement...about 60 psi. The snow had some tracks in it so I had the choice of plowing through the fresh stuff (not easy) or trying to follow the tire tracks. I tried both but following the tire tracks is just easier with that much snow. However, as I rode down the tracks, my bike kept sliding off the side of the tracks and down into the snow. Keeping going was very difficult and going in a straight line almost impossible. The tires do indeed want to punch all the way through the snow to the ground but that's not necessarily a good thing.

After struggling with sliding off the tire tracks, I decided to let air out of my tires and see what that would do. The difference was like night and day. At around 20 psi, the tires started to float across the car tracks instead of driving through them. Staying up on the packed part of the tracks became much easier and the bike tracked better. The tire tracks were no wider than before, however. And in snow pack you are very unlikely to run across anything hard edged enough to cause a pinch flat.

On today's ride, I did notice that even at a low pressure, the packed snow had enough soft spots that it kept throwing me off my line. Several times, it threw me off enough that I had to pop out of the pedals (another aspect of riding in snow is that clipless aren't difficult to get out of but that's a different thread) and stop. It took a while for my mountain bike brain to kick in and start riding the packed snow like sand, instead of like a harder surface.

When you ride in sand, it's best to sit up and even lean back on the bike. The idea is to pull your weight off the front wheel so that it doesn't dig in as bad and floats over the sand while your rear wheel - which is going to dig in anyway - provides the drive. Get into a lower gear (but not too low) and spin your way along through it. Works the same with snow and packed snow. Try to float the front wheel over the snow as best you can. Again, a lower pressure in both tires causes them to float rather than dig into the snow. Front suspension (perhaps even dual suspension) allows the tire to float more and dig less.
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