BY T . J . KROB
The Complexities Of Ski Design
Through the years snowmobile manufacturers and aftermarket companies have continued to evolve the layout of an essential part bolted to the bottom of every snowmobile spindle – the ski .
Let ’ s start with the raw materials : One could say they ’ re semi-consistent for the past several decades . After the sport moved away from steel and aluminum skis in the 1990s , the use of the material family of plastic polymers has been far reaching , with many applications . They can be molded , extruded and otherwise designed into complex shapes that all start from a fossil-fuel-based petroleum compound .
The thermoplastic nature of the material found in skis segregates it into a family that becomes pliable at elevated temperatures but then solidifies upon cooling , yet it can be reheated and reshaped . These are different than the thermoset type , which form irreversible bonds and shapes that cannot be altered upon reheating .
Further , this group has a very high molecular weight , meaning the long polymer chains transfer load more effectively to the chain ’ s backbone , drawing strength from the intermolecular interaction . To avoid brittleness , varied plasticizers can be added to keep the chain / product mobile and flexible in its fi n a ls t a t e .
Zeroing in more specifically on typical snowmobile ski material – polyethylene ( or ultra high molecular weight polyethylene – a . k . a . UHMW ) is durable and resistant to chemicals , and the poly gathers its strength from polymerization with ethylene . You may see UHMW stamped into some skis , but the mateiral is also found in skid plates and is widely known in manufacturing .
The cross section of the ski varies , from being thick in some spots to control stiffness to having thinner areas , ribs or cutouts / webs that shed weight while offering increased flex and some energy absorbing capabilities . The skis are , afterall , the snowmobile ’ s first line of cushion defense ahead of the shock package when impacting hard , whooped out snow .
Moving beyond the material of the ski , what ’ s most important is how the ski interacts with the snowy or icy surface . In previous Snow Science articles , we ’ ve noted that snow is an extremely temporal and ephemeral substance . It is one of the few creations that exist near its triple point – a material which in current state is a solid , a few degrees warmer turns into a liquid , or can reside as a vapor among itself at the same time .
The groomer runs over the trail and mechanically adjusts the snowpack by breaking down long arms of individual flakes and turning them into tightly packed “ balls .” Traveling over the snow immediately following the groomer , the surface often feels soft . But additional freeze time makes it much firmer . We ’ ve also all ridden down a trail and seen the grooves left by other machines ahead of us . Sometimes your ski and keel may fall into this groove and lead to following or unwanted darting in some cases .
A keel can take on a myriad of shapes depending on the goals of the manufacturer during its design . Long , deep , squared keels are ideal for aggressive , loose-snow riding . Such keels provide bite when turning . A shallower keel that doesn ’ t run all the way from the front to the rear of the ski will produce lighter steering with less feedback – but often has less turning ability .
Seeing a ski keel in 3D , though , is more important than just analyzing its length and total depth . The keel ' s side profile has received attention in recent years to fine-tune keel shape beyond a flat protrusion into a rocker shape . This allows it to have more keel height directly below the spindle and then tapering to have less at the front and / or rear .
Taking another slice of the cross section illuminates that keels needn ’ t be flat / straight / vertical on their sides . Skis can have a front / rear look of a keel that is 90 degrees square to the snow . But others can lean outward for some draft and snow shedding ability , while still others have a reverse lean inward , creating an hourglass appearance that channels the snow into a tighter pocket – where keels then can leverage the packed-up snow to turn against .
Multi-step keel designs leave three contacting levels to dig into the snow ( the highest wings , a first vertical step , then the final bottom vertical step where the skag mounts ) as an aggressive method to ensure positive cornering and handling . Clever companies can integrate one , two or even three sets of keels with skags to serve a multitude of riders and snow conditions , with each one offering a distinct experience and handling trait .
Another surface modification ski creators leverage is the induction of snow to the underside of the ski . The tip is the first part of the ski to contact the snow surface . Whether it ’ s a firm trail or mountain fluff will govern how snow passes the underside surface to glide with ease or pack the snow to provide lift . A tip that flares up and back will allow the snow to glance off the impact and disperse it sideways , like a V-blade snowplow driver . A tip design that flares toward the incoming snow – acting as a cup to capture it – will provide more lift by forcing snow underneath the ski .
Of course , the amount of snow “ consumed ” by the ski is governed by its overall width . A wider ski will exert less pounds per square inch of pressure on the snow , spreading the load over more snowflakes and sinking less into fluffy pow . Conversely , a narrow ski glides more readily through / across the pack with less resistance but sinks in powder . Therefore , a careful blend must be obtained to float or skim without translating into odd steering behavior – or being too wide overall to fit between trees or lean up onto an edge .
At the rear of the ski , attention has also been paid to the tail geometry for several reasons . A totally flat rear tail isn ’ t ideal for sleds with a reverse direction option , as the back of the ski has the potential to dig downward and restrict rearward motion . Thus most skis
40 / FEBRUARY 2025 / SNOWGOER . COM