As far as Canadian - someone asked if both riders use the mountain strap/center bar. For us, no. Typically, the driver, person on the right side of the sled, uses both handgrips, Passenger holds end of bar with left hand, shoulder strap of backpack on the driver. That's what works for us, mostly because we're not really on the same page wrt steering - it is pretty much impossible to turn the bars with one hand on grip, one on mountain strap. If BOTH riders were on the same page/of the same mindset as far as steering, that could work. I like having control of the brake, though.
You need a fairly narrow left hand and/or long grip area to make that work. I've been planning on mounting a bar end off a mountain bike on the left side just for the passenger. For us, it works - the driver steers, brakes, throttle, passenger is just ballast.
With some of my cohorts, we ride seamlessly. I'm normally driving - scarily enough, I'm the least jongtastic in my group on a sled. Newer passengers, if I need them to lean more uphill, I tell them "your side," if that's not enough, I left elbow them til they get the point

.
If you're sidehilling Canadian, it often helps a LOT for the downhill side person to put their rear knee on the seat. GENERALLY SPEAKING, with my sled-deficient friends, I tell them NEVER to put their knee on the seat - sleds only know WHERE your weight is interacting with the sled, and respond to that. MOST of the time, knee on seat = stuck or tipped over. Unless Canadianing + sidehill. Even with me on the downhill side (I'm big), we can sidehill pretty effectively if I put my knee on the seat.
Upper bodies don't need to be close together. Sometimes, I get on with a newer person, they crowd me in a big way. No, stand up. Upper bodies don't have to be all cozy - again, all about the feet.
Probably the biggest thing I've learned in riding sleds is simple - they like to be horizontal OR slightly rolled uphill/into the turn. Once they go past horizontal, they're hard to get back. Keep it "on edge" a little, they're happy. Getting new people to keep that in mind when Canadianing is hard - they'll often let the sled be truly flat, not account for the depression in the snow BEFORE they get to it, all of a sudden it is a scramble to get on the high side. If the sled had been a few degrees tilted in the correct direction *before* the depression in the snow/low spot/whatever, it'd likely have sailed right over it. Anticipating the next thing plays a huge role.
Bookmarks