SkiBike Design Part 4 - By Wayne Richards

Posted: Sunday, 25 March 2012 by Mark Kinnon in Labels: ,
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Skis, now there's a rather fundamental requirement in ski biking that we need to be using skis, but they come in so many varieties and forms that it is actually quite complicated to choose what type you actually need. For the moment lets discuss "blade" and "short ski" types for the moment.

Blade skis are typically less than 1.0 metre in length, originally designed around the need for mountaineers to carry them up to the top of some peak, clip them onto their boot soles, and take the fast downhill route home using the last of the natural snow runs available. They had to be light, tough and quick to clip on as well as fun. The earliest forms I can remember were the "Big Foot" types of the early 80's, daft wide things with curves in all the wrong places, but never the less, did the job.

NISM skibike skis - but what should we be looking for in a Blade type ski?

However it soon became apparent that they could be used as on piste skis and a whole plethora of semi mini skis appeared, really short around 60cm’s. Now we regularly see the more useful 100cm mark and more recently, the emerging short skis at 120cm. More importantly though, they have become more ski than blade, proper release bindings, nicely curved edges that will hold carving turns, nice curved tails to allow tricks and stunts and composite construction, just like their larger cousins, to control flex and twist. One only has to look at the Solomon Crossmax 120cm and Atomic series of short skis, to see all the construction traits of a genuine on piste ski. Blade skis are certainly no longer the dead feeling lumps that we used to attach to our walking boots.

OK so without buying specialist ski biking skis ( which are available ) what should we be looking for in a Blade ski. Well the honest answer is there is just too many variables for me to be able to "road test" all brands and variations, but I've built up enough mileage on the types I have tried on my bike that I think I can start to make some assumptions. I specifically tried the extremes to see what differences there are.

OK then how do you pick a set of skis?

The extremes were wide, short, small radius and long radius. What am I talking about. Well have a look at any ski specification and somewhere will be a series of numbers giving length, width of the ski at the widest front point, width at the mid point and width at the tail. Now join the dots by running an imaginary line through those points over the length of the ski and an arc is formed. The really really important bit is that arc when angled into the snow, forms the radius of your turn. So then a skis specs could be L99.9: SC 105 : 80 : 100 : R 6.0. ( that’s a Salomon “Snowblade” ) That arc will shorten as the ski has G force applied dependant on whether the ski is soft or hard and the applied force. Blades seem to be mostly in the "hard as planks" category to cope with a wide spectrum of skier weights.

OK then how do I pick a set of skis, well that will depend on what your intended "usage" and your ability is. Do you mainly want to ski on pistes, more off piste perhaps, do you want to do ace hockey stops spraying snow over your mates followed by a 360 and a bit of backward skiing thrown in. Now throw into the equation your weight including your riding kit and your bike, your riding ability, your bike design, does it have suspension, there's just so many variables.

How do I pick a set of skis? - so many variables

Let's start with a relative novice looking to ride mainly piste ( lets be honest here guys and girls, you may think you spend more time off piste, but how do you get to that favourite off piste ) Look on line at a number of short ski sales sites ( www.theshortskishop.com are a good shop with lots of different blades ) and throw in your total weight to find the correct length, almost certainly you will be straight away 100cm metre or more. Now go to your bike and see if indeed two 100cm skis will fit without touching, using the axle points as the centre of each ski. If so now input your normal snow conditions, mainly groomed hard pack trails, back to the on line site and almost certainly it will be a relatively narrow waisted ski around 80mm at the centre of the bindings.

Now comes the conundrum, what radius ski for a novice. I found that the shorter radius skis are much easier to skid off the edge allowing easy skid turns ( and that is what a novice skier does and is taught ) and good controlled stops, now that is really really important. So back on line and find a narrow waisted, small radius ski to match your weight. My Salomon “ Snowblade “ would be a pretty good all round ski at L99.9: SC 105 : 80 : 100 : R 6.0. for most beginner / intermediate skibiker.

Equally a good ski biker on piste will choose a narrow ski ( allows a quick roll time edge to edge using the limited amount of loose snow to roll the ski over on ) but here's the difference, they would want to be carving nice radiused turns. Now using a bit of logic here, they also will be much faster over the ground creating a real problem for the ski. Try and do a 6.0m radius turn at 15mph and you can only imagine the G force created. The ski will quickly loose it's edge in the snow and begin to skid uncontrollably until the G force gets down to reasonable levels. So pick a ski with a longer radius. The wooden cored Gaspo Hot Stamp at 103-86-95 Radius: 10.9mts would be in this category.


What radius ski for a novice?


Mmmm controversial this one. A skier normally in off piste skiing would want a wide, soft ( more on hard v soft bending characteristics another day ) ski to float and support the weight of the skier, whilst allowing the ski to bend, ( forming an arc as side cut or radius is not going to work in powder snow ), to initiate the turn. Ski bikes in powder seem to be different, my experiences with a very wide pair of board style blades in fresh powder was disappointing to say the least. The Salomon SB10 at 128:106:122, ( radius I’m not sure as its not listed ) would be an example. The weight / drag of the snow over the tip, with the short length seemed to force the ski to rotate around the axle and seemed to want to dive the ski to such an extent that I seemed to be doing far too many over the handlebar dismounts that it became a problem. I had to have my weight so far back to counter this that it just felt wrong ( and if someone is thinking that's what they do when skiing off piste, then go and learn to ski off piste correctly ). Also that wide waist made piste skiing really ponderously slow to go edge to edge as there was insufficient loose snow beneath to roll the ski over on ( due to the wide waist ) and by consequence felt really “clunky” as you went through the middle of the turn. Not nice.

Just to confirm my suspicions I changed to a much narrower ski with a reasonably wide tip and they seemed to work a treat. My gut unscientific thoughts are that ski bikes initiate the turn in powder by simply steering the ski and leaning the bike which a skiers knees cannot do, creating a natural "berm" deep down in the snow, with the rear ski now passing over the already compacted snow, creating the support that much wider and longer skis would normally be doing. It's only a theory and I'm sure many will disagree but it does seem ski bikes do behave differently in powder than a skier. . Now I know other manufacturers such as Lenz do like this wide style ski on their bikes so perhaps there is bike setup or even snow conditions between Euro and American mountains that maybe coming into play here.

OK the snow park junkies, yep there's twin tip blades out there specifically built for the snow park, tough, built typically of a wooden core, strengthened edges, they are just for you. Downside they are heavy and due to the twin tip, have a much shorter contact area on the snow. Specialist ski for a specific need.

OK so where have I got too on my bike, I looked at the 80cm I picked on eBay for a pittance, and put them aside, they just look wrong, too weedy for my 90kgs + bike and kit. Bought a pair of Solomon Snowblade’s and set to and learnt to ride. Then tried a pair of Solomon One|Ten’s as a powder ski, really disappointed, and put them too aside for the moment. Now trying Gaspo Hot Stamp 99 long radius blades, these seem really nice and hold quite a good edge, but I wouldn’t recommend them to start with, as they are quite hard to skid stop in a controlled way, preferring to arc the turn.

What would I like to try next, a 80cm front and 120cm rear as I have this theory that particularly the peggers amongst us, put a lot more energy into the rear ski by the way we ski and as the rear ski is doing the majority of the work, needs to have a longer edge and snow contact area. Remember some time ago I mentioned that my bike has a 60 / 40 weight bias to the rear ski and most will have nearer 70 / 30, which should dictate a long and short ski to ensure equal weighting on both skis. I think also that the ski bob designs have headed in this direction. But it would mean real surgery to most bikes which would need the rear swing arm shortening to get that rear ski into the right position.

So then if I was building a ski bike, what would I fit. Well eBay and other similar sites have some real bargain blades in the summer and spring, the most I have paid is £ 70.00 for an almost new Solomon blade which has been very good to learn on and surprisingly good as a powder ski. It's specs are L99.9: SC 105 : 80 : 100 : R 6.0. which puts it into that medium category, a good start. It's one downside is that it is not a wood core and thus one has to be “Uber” careful how you mount the adaptors and that will be my next chapter, ski mounts and your bike. And that is a really really thorny subject.

Looking for parts to build a skibike? Or perhaps one ready to ride away? See our Parts For Sale page here.

Read part 5 here

3 comments:

  1. tjbb says:

    Great information here. Thanks Wayne, much appreciated.
    Tim Brooking

  1. Unknown says:

    I'm gathering parts for 2 ski bikes right now. Looking at 100cm skis and finding that kids' skis are a fraction of the cost of "snowblades" or "skiboards". Kids' skis are surely much less stiff than the adult snowblades or skiboards but the latter is designed such that the adult's weight is almost 100% over 1 ski during a turn whereas I'd think on a ski bike the weight is distributed more evenly over both skis during a turn - that leads me to think a kid ski designed for someone half my weight might be just right for a ski bike. Thoughts?

  1. Don't bother with kids' skis, a child weighs what 20-30 Kg? An adult on a skibike could weigh up to 100 Kg. Those who've tried it find that skis snap frequently. There's plenty of Salomon SnowBlades and the many clones available for under £50 in the UK. You'll even find reasonably priced stock right here... http://www.skibike.me.uk/p/skibike-parts-sale_15.html