In Search of the Perfect Telemark Ski Binding

Nov. 23, 2008
The design of a good ski binding is an exercise in engineering compromise and a lesson in the use of analysis tools.

Who, what, where
Authored by Stephen J. Mraz
Senior Editor
[email protected]

Key points
• Telemark skiing combines cross country with downhill.
• FEA cut weight off G3 bindings without a strength loss.
• Physical tests verified FEA results.

Algor Inc.
G3 Genuine Guide Gear Inc.
North American Telemark Organization
U.S. Telemark Ski Assoc.

Telemark skiing might not have as many devotees as downhill and cross-country skiing, but its back-country setting — off the beaten trails with plenty of fresh snow and wide open vistas — has attracted a loyal following. And as more people take up the sport, a hybrid of downhill and cross-country skiing, the equipment is changing to accommodate a wider variety of telemark (or freeheel) skiers. So G3 Genuine Guide Gear Inc., North Vancouver, Canada, decided to update its popular Targa binding, the device that holds a ski onto the skier’s boot. “The introduction of plastic telemark boots, and the trend for those boots to become larger and stiffer, led to a lot of broken bindings,” says Cameron Shute, a senior product developer at G3. “Unlike Alpine (or downhill) bindings which connect at the heel and toe, telemark skis have the physics stacked against them in that they only connect at the front of the boot with a plate or duckbill.”

Just what is telemark skiing?

Take downhill or alpine skiing, mix in aspects of cross-country skiing, and do it in the back country, far from the ski lifts and crowds. The result is what's called telemark skiing. The key difference in equipment for these three types of skiing is the binding, the mechanism that holds the ski to the skier's foot. In Alpine or downhill skiing, skis rigidly attach to the heels and toes of tight-fitting boots, giving users execellent control of the skis as they schuss down steep hills. But boots and bindings make walking and climbing snowcovered hills somewhat awkward and exhausting. (Hense the ski lifts.)

Cross-country bindings, on the other hand, let skiers lift their heels from the ski, so they can climb hills and maintain a walking-like gait to glide across level ground. The loose heel connections means skiers cannot guide or control their skis well enough to go downhilling through knee-high powder.

Telemark bindings represent a hybrid. A special boot connects to the skis at the toe while a pair of springs in the binding hold the heel to the ski. (For climbing, telemark skiers apply skins to the base of their skis, whic, at one time were made of seal skin, but now are made of plastics or mohair.)

So G3 set about to develop a new binding with the idea of making it stronger but also lighter, more dependable, and more controllable for skiing downhill.

Keeping it flexible
Key to the Targa binding redesign are compressionspring cartridges, a common feature on modern telemark bindings. A pair of cartridges, one per side, mount in line with a cable that encircles the back of the skier’s ankle or heel. The cartridges pull the heel forward, forcing the boot into the binding. They also apply a load to the heel to keep it from lifting. As manufacturers made boots and cartridges stiffer to help downhill performance, it became more difficult to do the touring or cross-country aspect of telemark skiing. “Flexing stiff boots and compressing the cartridge springs during each step adds up to a huge amount of energy,” says Shute. “The springs made it energy intensive just to walk.”

To counter this trend, G3 started making several varieties of cartridges with different spring strengths to meet different conditions (aggressive downhill, level cross country, and deep powder, for example). The company also uses aircraft-quality cabling for strength and light weight.

Another important feature that lets the new Targa Ascent binding handle downhill and cross-country skiing is the free-pivot system. Skiers put the bindings in touring or ski mode by using a ski pole’s tip inserted into a strong plastic cup on the toe section and sliding it from one mode to the other. In tour mode, a toe plate freely pivots on a stainless-steel axle. This makes it easier for skiers to go up on the balls of their feet. The flex point was biomechanically determined to give a natural feel and an efficient cross-country skiing-style stride. This lets telemarkers cover ground on their way to those hills and vertical drops covered in undisturbed powder.

Not your everyday snow shovel

Though G3 Genuine Guide Gear is probably best known for its ski gear, it ahs long designed and maufactured snow shovels that come in handy when a ski buddy has been buried by an avalanche.

G3 shovels are light, weighing under a pound, and relatively strong. Their aluminum blades are formed while soft, then heat treated to boost yield strenght by 500%. The blade and connector tube are then TIG welded. An ergonomic plastic handle finishes off the design.

But there are also details back-country skiers appreciate. For example, a watertight compartment in the handle can hold matches, batteries, or other emergency supplies. The handle also has small hooks molded in that let backpackers securely stow the shovel using ice-axe loops, common features on backpacks. And the shovel blades have slots that let back-country explorers attach skis to the shovel and contruct a rescue sled if needed. The company also makes two different styles of shovels with different blades and handles to suit different digging styles.

The company recently tried to update its shovels, concentrating on strength. "Avalanche debris tends to be really cohesive," says G3 engineer James Shaw. "It's chunky icy, not like powder snow." So he first considered an all-metal design to give the shovel more ice-cracking strenght. Aluminum was thought to be too soft as it gets damaged when hacking at icy debris. And more-durable metals such as steel would make the shovel too heavy.

So Shaw decided to try a metal-and-plastic design. The idea was to make the shovel body clear poycarbonate or a nylon, but with a cutting edge and reinforcements of steel. The design would be light, strong, and have a unique look. SolidWorks CAD and Algor FEA software indicated the shovel would withstand all anticipated loads and abuse after stress analysis indicated areas that would benefit from beefing up with steel and others where shaving off steel would save weight.

With the design complete, G3 had some prototypes built and this is where the design headed south. The plastic blade could not be made to the correct dimensions. It would shrink, which in turn meant the metal reinforcements didn't fit without distorting the blade. As a result, the new shovel design still sits on a shelf at G3.

A skier ready to go downhill again inserts a ski-pole tip into the cup at the back of the bindings and slips it into ski mode. It slides a steel retainer into place about a rigid steel retention bar, which locks the toeplate to the ski, thus limiting how high the skier can lift his or her heel. It also tightens the cable with its compression springs, further stiffening the connection between heel and ski.

Analysis and refinement
Once the concept for the redesign was developed, the G3 team examined each part to reduce its weight and boost its strength. For example, the sheet-metal base plate that screws to the skis and holds the bindings to the skis became 200-gm lighter after testing and FEA revealed that two extra screws on the midplate would keep the binding on the ski. This let a sheet-metal version replace a heavier forged piece. Tests also determined that screws at least 1 in. away from each other do not weaken the ski or the plate.

Another component that got changed was the toe box, the area into which the toe of the boot fits. Other bindings did not include a box, just upper support members. But this part often broke because it flexes slightly. G3 added the box for structural strength and riveted it together. “Rivets are stronger and more flexible than welds,” says Shute. But rivets are also just as permanent and difficult to repair in the field if they break. “Many of our customers rely on our equipment, so we try to ensure it won’t break, despite heavy use,” says Shute. “But if something does break, we try to make sure the skier can repair or replace it in the field.”

Analysis also revealed that the design of the cable guides, the small component that directs the cable up and around the side of the binding, was causing stress concentrations. “So we angled them more and gave them a larger, more-rounded diameter which reduces cable fatigue, a cause of cable failure,” says Shute.

Field testing and years of telemark-skiing experience also helped the G3 team. Anti-ice plates, for example, were added to the front and back of the boot where it meets the skis. “These were problem areas because of ice buildup,” says Shute. “Ice interfered with the bindings and was time consuming to remove.” The plates are of a hydroscopic material to which ice won’t stick.

Material selection was important. Plastic components, for example, had to maintain critical qualities despite cold weather. So engineered thermoplastics were the typical choice. Metal parts are mostly 7000 Series aluminum, but 300 Series steel goes where strength is critical.

The resulting Targa Ascent binding took less than a year to redesign, but spent almost the same amount of time in testing to assure the gear is top notch. The binding has earned several recreationalindustry and ski-magazine awards. What makes me the proudest,” says Shute, “is that professional explorers and guides are choosing the Targa Ascent binding.”

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