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A ski-bike is a magnificent contraption that uses the basic elements of a bicycle fastened to downhill skis to ride down a snowy slope.

My first attempt at creating a downhill ski-bike resulted in a fully functioning prototype and was overall, a success. It performed as I suspected it would. The ride blended attributes of skiing, snowboarding and biking to great effect. You can find a link to my first iteration here: How to Create a Downhill Ski-bike

Despite the first ski-bike's admiral performance, test riding it revealed there were opportunities for improvement so I developed several design specifications and characteristics that would improve the ski-bike's durability, performance and ease of use. This Instructable chronicles the design improvements and changes that I made to create my second downhill ski-bike. Each step focuses on a specific attribute that I improved.

To avoid creating confusion, from this point forward I will refer to the first ski-bike as Ski-bike 1.0 and the ski-bike created in this article as Ski-bike 2.0.

Step 1: Bike Frame

After a few of my friends rode Ski-bike 1.0, it was apparent that the size of the bicycle frame was too large for most riders. The extra large frame was heavier than the riders were used to and more difficult to maneuver. The shock on the bike frame was also designed for larger riders so smaller riders were not able to fully utilize all of the shock absorbing advantages.

For these reasons, I chose to use a small sized mountain bike frame for Ski-bike 2.0. This would allow smaller riders to be more comfortable with the points of contact, and larger riders to ride the bike with few, if any, trade-offs.

There were two features of the bike frame from Ski-bike 1.0 that I wanted to keep the same. The first was to utilize a suspension driven frame and the second was to have an aluminum frame for it's excellent strength to weight ratio.

Step 2: Mounting Brackets

My top priority for Ski-bike 2.0 was to design and build the mounting brackets out of steel to achieve maximum rigidity and durability.

For Ski-bike 1.0, I lowered the axle height from the typical 13 inches for a mountain bike to 11 inches in order to lower the center of gravity and improve handling. The modification was effective so I expanded on that strategy for Ski-bike 2.0 by designing the axle height to be 9 inches.

Building the mounting bracket was a five step process:

  1. Cut the angle iron and tube steel to the lengths predetermined by my design.

  2. Weld the pieces together.

  3. Build the hub and axle assembly.

  4. Drill holes in the angle iron to line up with the ski binding screw holes.

  5. Drill the holes in the front of the brackets for the eyelet bolt (discussed later).

To create a basic hub and axle system, I used a standard 3/8 inch threaded rod as the axle and purchased plastic bushings (from the retailer Igus) to provide a low friction barrier between the axle and the outer steel sleeve. The internal diameter of the bushing was chosen to match the axle and the internal diameter of the outer steel sleeve was chosen to match the outer diameter of the bushing. This resulted in a free rotating axle with very little unwanted play. I also added lock nuts to the front and rear axles to control the longitudinal pressure exerted on the hub delivered by tightening the outer bolts over the dropouts.

Step 3: Ski Type

As I demonstrated with Ski-bike 1.0, a set of downhill skis cut down in size did work to build a functioning ski-bike, but there were some serious drawbacks. Since I shortened the ski length, I couldn't use the ski binding screw holes so I had to drill long wood screws up through the bottom of the ski to attach the mounting bracket. This method was not secure enough for extreme or long-term use. Another drawback was that the ski could break open or separate on the cut steel edge, ruining its performance, and becoming a safety risk.

A much better option was to use a set of twin tipped ski blades (aka ski boards or snowblades), which allow for the same control sliding backwards as forward. Ski blades are similar to modern downhill skis, but are significantly shorter, often coming in lengths between 90 and 100 cm. This length range has become the unofficial standard for ski-bikes. For Ski-bike 2.0, I obtained a set of ski blades that were about 94 cm in length.

The width of the skis was also a factor to consider. Despite being similar in width, I could immediately tell a difference in the performance of my chopped downhill skis on Ski-bike 1.0 and my slightly wider ski blades on Ski-bike 2.0. The extra width increases the amount of leaning needed to catch the ski's edge and carve through the snow. One is not necessarily better than the other; it comes down to the rider's preference.

Step 4: Fork Travel

Here are two technical bicycle terms that will help clarify the following section.

Fork Travel - The amount the suspension fork can compress. The larger the amount of suspension travel, the longer the fork is.

Head Tube Angle - The angle the center line of the head tube makes with the horizontal plane. A steeper head tube angle will steer a bike more quickly whereas a slacker head tube angle makes it easier for a bike to travel in a straight line. Head tube angles range from about 66 degrees (downhill mountain bikes) to 74 degrees (race orientated road bikes).

During its days as a regular mountain bike, the Ski-bike 2.0 frame had a fork with 100 mm of travel. When converting it to Ski-bike 2.0, I replaced the original fork for a fork with 130 mm of travel. The 130 mm fork had 30 more millimeters of travel than the 100 mm fork and was therefore longer. This increase in length raised the head tube and reduced the head tube angle which gave me more confident steering and control when pointed downhill.

The amount of fork travel paired with the height of the front and rear axles (based on the mounting bracket dimensions) determines the head tube angle. This in turn affects the steering and handling of a ski-bike. Since every bike frame comes in several sizes and has a different geometry, I can't say that there is a single, optimal amount of fork travel for all ski-bikes. It comes down to personal preference of the rider and the terrain.

Step 5: Footings

I really liked the footing setup I used for Ski-bike 1.0 because it provided the familiar feeling of using standard bicycle cranks and pedals and allowed me to change the position of my feet depending on the situation. There were a few drawbacks to this setup though. Without the resistance from the chain and rear wheel, the cranks spun freely, which as a cyclist, I wasn't used to. Another drawback was that the drive side crank arm still contained chain rings. During a crash, the teeth of the chain rings could potentially injure a rider.

For Ski-bike 2.0, I came up with the idea of using unicycle crank arms. Unicycle crank arms worked great because they still allowed the pedals to change position, had no chain rings to worry about, and were available in a variety of lengths. I decided to use really short crank arms to remedy the uneasy feeling of pedaling long crank arms with zero resistance. Having short crank arms resulted in a much smaller rotational diameter of the pedal, minimizing the effects of spinning the cranks with zero resistance. Another benefit of shorter crank arms was the increased clearance with respect to the ground.

I chose to use mountain biking platform pedals for Ski-bike 2.0 because they have a wide foot platform and large studs for extra grip.

Step 6: Ski Rotation Control

Unlike a bicycle wheel that's ready to contact the ground anywhere in its rotation, it's imperative to always keep the skis on a ski-bike with the bottom sides down. Ski-bike 1.0 had no system in place to keep the skis from over rotating in either direction. This potential problem was controlled by limiting Ski-bike 1.0's use to stable snow conditions and no large jumps.

Ski-bike 2.0 on the other hand was designed to be ready for anything. The front ski was controlled by a bungee retention system on the front of the mounting bracket. The bungee was in constant tension while the ski was on the ground, always trying to pull the front tip of the ski upwards. The bungee was threaded through the eyelet bolt on the front of the mounting bracket and lashed into a loop using sturdy stainless steel wire. The top of the bungee was lashed into a loop with more wire, looped over an "S" hook, and then the "S" hook was hooked to the bridge of the bicycle fork. I cut the length of bungee to achieve the right balance of tension. Once airborne, too much bungee tension would pull the ski tip quickly towards the handlebars and too little tension could allow the ski tip to dive into the ground.

For the rear ski, I was going to rig a bungee retention system similar to the front ski, but I came across a torsion spring that seemed to be the right size and have an adequate spring rate (i.e. strength of the spring). The spring had an internal diameter larger than the axle's lock nuts so it slid right over the top and pressed against the underside of the mounting bracket and the axle cutout of the bicycle frame's dropouts.

One key attribute of these two systems is that they both can easily be disengaged when needed, such as during transportation.

Step 7: Paint Job

This step is entirely optional, but very effective at giving the project a professional and completed look. I had the bicycle frame and mounting brackets powder coated which is very durable, but requires the parts to bake in an oven to harden the paint. Since the skis contain a lot of plastic that would have likely melted during the baking process I was not able to powder coat them so I simply spray painted them instead.

I chose a dark metallic blue color for the frame to accentuate it's shape when viewed with a white snow background. The skis and mounting brackets were painted white to blend into the white snow background to create an illusion of the bike just floating over the snow.

Step 8: Conclusion

The performance of Ski-bike 2.0 was a giant step ahead of Ski-bike 1.0. I was able to confidently ski-bike down a legitimate ski hill as fast as a typical skier or snowboarder. The front ski dug its edge into the snow when I turned the handlebars and allowed me to carve sweeping turns and stop whenever I wanted. Every improvement was noticeable.

Here is a quick summary of each improvement made to build Ski-bike 2.0 and the resulting performance increase:

  • Using small sized full suspension bike frame = lighter weight and easier to handle
  • Building mounting brackets out of steel = noticeable increase in rigidity and ability to fasten to ski via screw holes
  • Lowering axle height via mounting bracket dimensions = lower center of gravity made turning and leaning easier and more confident
  • Using twin tipped ski blades = allowed sliding backwards and the use of the screw holes for secure fastening to mounting brackets
  • Increasing fork travel reduced the head tube angle = more confident steering and control when pointed downhill
  • Using short unicycle crank arms = increased ground clearance, no chain rings to worry about, and minimized feeling of no resistance
  • Creating a bungee and torsion spring rotation control = prevented front and rear skis from nose diving while airborne

Ski-bike 2.0 was a major success. It achieved every performance goal that I set and more importantly, it was an absolute thrill to ride. While I will ride Ski-bike 2.0 as is for a while, I can't help but contemplate ideas for Ski-bike 3.0. Be on the look out. But until then, check out the video highlights of Ski-bike 2.0 in action!

<p>Really nice project! I love that white paint on brackets and skis. Those little cranks are nice touch also. I'm just curious how much does the whole thing weight, including skis? My frame is from cr-mo and i think that sub 12 kilo should be achievable...</p>
<p>Thanks! I have never weighed the ski-bike so I can only guess, but I bet it's close to 12 kilos. A sub 12 kilo goal is definitely achievable. My brackets connecting the skis to the frame are way over built and as a result are heavy. My next version will have more refined, lighter brackets. Remember to post a picture here once you've made your own using the 'I Made it' button!</p>
<p>How long are the skis that you used? And what bike frame did you use?</p>
<p>The bike frame is a women's K2 Ridgeline and the skis are 94cm long.</p>
<p>How would you take this on a ski lift?</p>
<p>You just walk it up to the line and once the chair comes around, it hits the bike's frame under the bike seat. Once you sit down and start moving forward (still holding onto the handlebars), you can lift the front end up so the bike seat is resting on the chairlift (close to a vertical position). From there you just hold on until you're at the top and lower the bike when you're feet are about to touch. It was pretty easy!</p>
<p>Seems like it would be a blast to ride.</p>
Version 3.0 should offer brakes on the handlebar like a regular bike, not for stopping the bike, just slowing it down. But great job, had a lot of improvements from 1.0
Nice but I don't see the use for the pedals. Anyway got my vote hope you win!
<p>Offset pedals allow inside foot to be higher for increased ground clearance when leaned over for a turn. Pedal strike is the bicycling term for pedal contact with ground during hard turns (and can be a problem for fixed gear bikes)</p>
OK I get it cool!<br>
<p>Just wondering how much of a hassle ski areas give you to bring this on the slope. Around here I am guessing they wouldn't allow it.</p>
<p>I would strongly advise calling ahead and asking if the hill allows ski-bikes. I found a hill in my area that allows ski-bikes through the <a href="http://www.americanskibike.org/" rel="nofollow">American Ski-bike Association</a> website and wasn't hassled at all. Even the chairlift operators thought the ski-bike was cool! </p>
love the idea, and i have always wanted one. And I thought about making a BIG wheel version for big kids
<p>Very nice design! To me however, it looks like a great way to break my neck. </p>
<p>Hmmmm I'm thinking for my skill level something along the lines of a 3 ski would work for me. Low to the ground like the old school big wheels. I think you did an excellent job!</p>
I've seen lots of these over the years and have actually aspired to build one up myself, but the ski portion of the build always threw me for a loop and degraded throughput of the project. Your ski option is TOPS and it will serve to be my platform of the build. This is [by far] the best ski bike build I've seen to date; very nice instructable as well.
<p>Cool!</p>
<p>This is amazing. You have my vote. </p><p>I was thinking. Would it be possible to a make a bike snowboard system? Mount a full suspension bike to a snowboard. You would loose handlebar steering though. </p>
<p>Thanks! Yeah, there are a few people on Instructables that have made them. They cut the snow board into two pieces and attach them to the fork and dropouts just like a ski-bike. It's basically like having really wide skis. I think it'd be pretty difficult to maneuver without cutting the board.</p>
<p>Well, this certainly got me reading. As someone rather familiar with bicycles I am looking at some of the old frames I still have with the idea of making one of these someday.</p><p>The <em>triangles </em>for skis look somewhat heavy, any thoughts regarding that?</p>
<p>I'm glad it got you thinking! Yeah, welding the mounting brackets out of steel certainly wasn't the lightest option available, but they're not boat anchors and in the end it's just sliding down a hill. I would guess that properly waxed skis would have more of an impact on speed and control going down the hill than the weight difference between steel and say, aluminum.</p>
<p>Thanks, will see how it goes eventually, now it's already spring here, so not to soon though. (:</p><p>By the way - I love the unicycle crank solution. The unusual position if using pegs vs no resistance was always one of the thoughts I had regarding snowbikes.</p>
<p>Looks amazing. Probably would kill myself if I use one of these. But it's brilliant. The bike pedals are a nice touch. If it was static you would probably not be able to do all the possible tricks. <br>Great job! Very nice tutorial too.</p>
<p>really cool, have you considered pegs or motorcycle foot rest in place of the pedal for better clearance and stability?</p>
<p>I did consider static foot pegs, but I thought having adjustable pedal positions would give it more of a bicycle feel and I definitely think it works! If you're turning right you can rotate your right foot to the rear position and that gives you a bit more leverage when pushing the rear end of the ski-bike into a side skid.</p>
<p>Whoa, this is beautifully done! So much cool.</p><p>Prior to reading, I was really curious about the pedal situation, and I wondered why you didn't opt for straight foot pegs. But I liked your explanation in step 5, and it makes complete sense to me!</p><p>What about torque-y issues with the front ski where it connects to the fork? Ever had that front ski just ripped off the fork by a weird bump or turn?</p>
<p>Thanks for the feedback, I'm glad you like it! I'm sure I fully understand what you mean by torque-y issues, but I made sure the axle bolts were tight throughout the test riding. The front ski can rotate around the axle fairly easily so it's unlikely to be ripped away from the fork. </p>
I think "torque-y" might have been the wrong word. :)<br /><br />I was thinking about lateral strength, say if you catch an edge or hit hard sideways into a bump. Regardless, this is cool and I want to make one!
This looks so fun! I can tell you put a lot of thought into the improvements for 2.0.
<p>This looks amazing! It looks so easy to ride! I like your bungee ski control idea! It looks like it works really well. </p>
This is just incredibly creative and well thought out. I love it!!!!!!! Always been interested in making one.

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Bio: I'm an engineer who loves to solve problems by creating new products and finding useful ways to improve existing products. I like working in ... More »
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