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Old 01-01-10, 07:02 PM   #1
AngrySaki
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Well that didn't work... (front ski)

Built a crappy "ski" with a couple of friends for a mountain bike for use on back roads/fresh snow/trails, but it ended up being worse than the regular front wheel (except while going downhill at a decent speed).
These were the best runs. We never made it more than 50 meters or so.

I think I might try a double ski design (so I can't fall over). Has anybody had good luck with any designs? I don't hope to go fast, just to be able to get over more terrain than I normally do without having to get off and walk.
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Old 01-01-10, 07:23 PM   #2
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Nice...I have thought about buying a cheap snowboard and trying it.
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Old 01-01-10, 07:36 PM   #3
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I think I might try a double ski design (so I can't fall over). Has anybody had good luck with any designs? I don't hope to go fast, just to be able to get over more terrain than I normally do without having to get off and walk.
google image search:
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Old 01-01-10, 07:45 PM   #4
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I think the design of putting it over the front wheel is great.

To me it just doesn't look like your ski is big enough.
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Old 01-01-10, 10:08 PM   #5
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I've always been intrigued by this idea. I'm not enough of a tinkerer to build one myself though.

Oh, and it was in Bobcaygeon where I saw the constellations reveal themselves one star at a time.
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Old 01-02-10, 12:17 AM   #6
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It sort of looks like a traction issue, have you tried a super aggressive spiked tire?
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Old 01-02-10, 01:00 AM   #7
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^ Agreed, and use some metal rails from an old-timey sled. They could reduce the resistance compared to the wood.
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Old 01-02-10, 01:51 AM   #8
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The old-timey sled doesn't steer well at all.
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Old 01-02-10, 08:35 AM   #9
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^ Agreed, and use some metal rails from an old-timey sled. They could reduce the resistance compared to the wood.
There is a piece of crazy carpet stuck to the bottom of the wood, but I think proper skis would work better, because they have a better edge.

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It sort of looks like a traction issue, have you tried a super aggressive spiked tire?
No, but I think i'm going to give that a try. Maybe a thinner tire with aggressive spikes would work.
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Old 01-02-10, 09:09 AM   #10
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You practically have to use out-of-the-saddle climbing muscles just to cross 50 yards of level ground. That to me says you need a more efficient ski. If you develop one, then you won't need so much power.

The video does have that exhausting look of the rider trying to pedal hard, but holding back at the same time to keep from overwhelming the traction of the drive wheel. I think that would go away if there was less resistance.

Last edited by garage sale GT; 01-02-10 at 02:36 PM.
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Old 01-02-10, 09:23 AM   #11
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^That's why I suggested the sled rails (not the whole sled, I realize that those things didn't steer so well). Something with less resistance that would also provide some side-to-side bite for control. Rails or something like them would help.
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Old 01-02-10, 11:23 AM   #12
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If that's the frozen yet crunchy type of snow that I think it is, it's gonna feel lik











Where'd my damn post go? There was a whole paragraph here the other day!

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Old 01-02-10, 01:34 PM   #13
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Folks have experimented with all kinds of hybrids using skis and bikes, but ultimately the best snow bike has proven to be the fatbike with its extremely wide tires.

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Old 01-02-10, 08:33 PM   #14
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I tried making a double front ski, sort of like in the picture thirdgenbird posted. It didn't work at all.
When you try and turn left, the bike leans right, and vice versa. I'm pretty sure it's because of the head tube angle and is something that would get worse as the skis got wider apart (I had my skis fairly wide/handlebar width). I also tried adding a sideways hinge for leaning when my original design didn't work, and that made it completely unusable. I'm going to try and add some sort of springloaded setup with bungee cords to the hinge and see if that helps in anyway.

For double skis to work I think you'd either need a bike with a 90 degree head tube angle (or a negative one), or you'd need to setup the skis to turn like snowmobile skis do (with each ski rotating from it's center point).
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Old 01-03-10, 07:48 AM   #15
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I'm still waiting for usable and affordable AWD MTB There were some ideas but none really took off:

http://www.popularmechanics.com/outd...s/1276766.html (2001)

Even though it looks like they still make them:

http://christinibicycles.com/bikes.php

Adam
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Old 01-03-10, 08:14 AM   #16
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I did have this idea of coupling a hydraulic pump to a freehub or disc mount which would give drive power to the front wheel. All it would require is a proper hydraulic sealed rattle cage style pump that mounts on a freehub or disc mounts and a device that secures the pump to the fork and rear triangle.

to make a tadpole work well on an upright, you need to have some sort of tilting mechanism when steering because your CoG is very high.
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Old 01-12-10, 12:08 PM   #17
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A bike is stabilized by a rounded tire that causes the bike to turn right when, for instance, the bike starts falling to the right, left when falling to the left. Let's just suppose the bike is falling to the right. This means there's a force vector pointing right (wrt the direction for travel) at the point where tire meets road. Since the center of gravity is above the road, you get a net torque vector pointing backward (right hand rule), throwing the bike back toward vertical.

Flat bottomed skis can't do that for you. It's why snowmachines are designed with double skis.

A pedal-powered snowmachine would be cool and is basically what's shown in the photo of the double-ski rig.

As AngrySaki hints, anything like a trike suffers from a nasty tendancy to flip on turning. It's how sidecar pilots "fly" the rig. They're treading a very fine line. Most side car rigs also swap the rounded motorcycle tires out for flat-bottomed automobile tires because they no-long make use of the cone-effect stabilization of rounded tires (there are exceptions with leaning-sidecar rigs and the new trike-scooter offered by Piaggio). Snowmachines are very intentionally built with a low center of gravity and will tend to slide sideways before they flip, but beware a patch of non-slippy stuff in the middle of a high-speed curve. This is not, however, a result of the rake.

The rake will require that the ski be on a pivot at the attachment point like a cross country ski is at the toe attachment point. It looks like this is the case in the photo and it is also how snow machines are designed. Otherwise the skis want to turn out of the horizontal plane.

You should really send that in to the Red Green Show... It's actually a credit to your biking skills what you kept it upright at all.

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Old 01-12-10, 12:30 PM   #18
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A bike is stabilized by a rounded tire that causes the bike to turn right when, for instance, the bike starts falling to the right, left when falling to the left. Let's just suppose the bike is falling to the right. This means there's a force vector pointing right (wrt the direction for travel) at the point where tire meets road. Since the center of gravity is above the road, you get a net torque vector pointing backward (right hand rule), throwing the bike back toward vertical.
Naaah. The bike can't tilt inward to counteract the fact that the center of mass wants to keep going in a straight line even as you turn, which apparently causes your weight to be thrown toward the outside of the turn.

When you steer a bike, you lean inward before the turn to counteract the centripetal force.

Try staying perfectly upright in the saddle relative to the seatpost on your wheeled bike. You won't be able to turn without tipping outward. Then try turning in the opposite direction you want to turn in, just for a moment, until the bike tilts, then turn in the other direction and complete your turn.

Since you can't lean a skibike which is forced to remain upright, it leans outward.

Also, if you draw four circles in the air to describe the path the tips and back ends of the skis would take if the bars were rotated, you will soon see that due to the steering tube's angle you're lowering the tips of the skis and raising the back, and the tip is inside while the back is outside, twisting the head tube of the bike toward the outside of the turn.

It would have effected the OP's single ski bike, but the ski is mounted on the wheel and is able to rotate. I believe the wheel has to rotate backward when the bars are turned away from center in order to keep the ski flat on the ground.

Last edited by garage sale GT; 01-12-10 at 12:36 PM.
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Old 01-12-10, 12:47 PM   #19
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I'm still waiting for usable and affordable AWD MTB
It would be nice to have one where the front wheel was powered all the time because if the front wheel is suddenly hit with power when the rear wheel slips, you just might get a two wheel spinout and loss of control. However, if you didn't have some kind of differential in there between the wheels, it would skid on hard surfaces and maybe snow also.
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Old 01-12-10, 01:57 PM   #20
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Well, granted it's considerably more complicated than the 1-paragraph explanation I gave which Jones (link below) describes as "not the whole truth." I was essentially just giving a layman's version of Timeshenko and Young, and closely paraphrases the fantastic Archibald Sharp, "Bicycles and Tricycles: A classical treatise on their design and construction,"New York, Longmans,Green, 1896. See Chapt. XVII. The book is available from Dover and contains a tremendous amount of what is still state-of-the-art bicycle engineering.

http://www.phys.lsu.edu/faculty/gonz...9no9p51_56.pdf
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Old 01-12-10, 02:53 PM   #21
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I saw a video somewhere (damned if I can find it now) where a guy had two small (1-2 foot) skis mounted on either side of his front and rear wheels, with his rear tire protruding enough so when the skis were flat on the ground he could propel the bike by pedaling, but as soon as he leaned the bike he was carving the skis. it was the best bike-ski design I have ever seen.
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Old 01-12-10, 06:41 PM   #22
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Ski Bike V2:


It actually works , and is better than a front wheel is deep snow.
My brother built it with an old downhill ski he bought from the thrift shop. The ski is worse than a front wheel on heavily packed/thin snow (like riding on a snowy road), but substantially better in deep snow. We went riding around and there was a few parts I couldn't ride on my regular bike, that he was able to because the resistance is lower (I could ride on them, but I'd have to be going at >80% so I'd burn out really fast and couldn't really get anywhere).
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Old 01-12-10, 08:38 PM   #23
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You want the most surface area you can manage.

Last edited by TFS Jake; 01-12-10 at 08:42 PM.
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Old 01-12-10, 11:42 PM   #24
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Awesome.
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Old 01-13-10, 12:15 AM   #25
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I went with the scouts to MT loon a few years back and the rented ski bikes for down hill riding, of course I had to try one. it worked well with down hill sking but this bike had a ski on both the front and back wheel

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