Photo by Tom Lippert: Seth skiing powder at Squaw Valley.All contents of this website Copyright 2011-2015 by Seth Masia. All rights reserved. No reproduction without prior permission.
Several years ago, Pete Wagner asked me to contribute some thoughts on the art and science of ski design. The resulting discussion lived for several years on the Wagner Custom website but got lost in a redesign, so I’m summarizing it here.
Buying skis has become both easier and tougher than it was 20 years ago. Before 1990, there were about 35 ski factories around the world, and they all made essentially the same product. The design of skis had been more or less frozen for several decades. The classic slalom ski was 205cm for men and 190cm for women, shaped 85-65-75mm. This gave roughly a 40-meter sidecut radius and a bearing surface of about 1300 square centimeters. The classic giant slalom ski was 210cm for men and 200cm for women, shaped 87-68-77mm — roughly 50 meters radius and a bearing surface of 1400 square centimeters. The big differences in skis were not in shape and size, but in flex and materials. Slalom skis were of fiberglass, GS skis of aluminum. Recreational skis were thinner (therefore softer) and made of less-expensive materials. Buying skis required a lot of trial and error to find the flex pattern that worked for your weight, strength, skill and snow conditions.
Today most of that trial-and-error is gone. You can choose a ski based on matching width and turn radius to the kind of snow you like.
For hard snow, get a ski with a narrow waist: 70mm or narrower.
For soft groomers or general western front-of-mountain skiing, get a moderate waist — 70 to 78mm.
For resort powder (with a firm surface underneath) get a mid-fat waist, 75 to 85mm.
For deep snow (with an unpredictable base beneath) get a fat waist, more than 85mm. If you’re big and heavy or carry a heavy pack, go even bigger: 95mm and up.
What remains is length and shape. Most men skiing at resorts can get along very nicely on a 165cm ski, most women on 155cm. If you’re stronger than average, go a bit longer but nowadays it won’t buy you a lot of additional stability. If you’re much lighter than average, go a bit shorter — it will pay off in improved agility.
Shape means sidecut. A deeper sidecut with a shorter radius carves a shorter turn. In general, this helps best on groomers. It won’t help in bumps, where you want the tail to release to avoid hanging up at the end of the turn. A good mid-fat nowadays has a shape close to 115-76-105, which gives a theoretical radius of about 12 meters and a bearing surface of 1350 cm2. Note that the bearing surface — the ski’s ability to “float” on soft snow — is similar to the classic straight slalom ski. So is the ski’s weight. But the agility — the ability to bend easily into a turn — is vastly improved due to a turn radius roughly 25% of the old long, straight ski.
So what shape should you buy? Start with that “generic” 115-76-105mm shape at your length, then blow the waist up wider if you’re going to ski a lot of soft snow, and pull it in narrower if you’re going to ski a lot of hard snow. If you’re an expert who loves to carve, go for a shorter radius. If you want to be able to slide the tail a bit in bumps and tight woods (or if you have to skid a bit when you teach intermediates) opt for a bit narrower tail.
That’s the basics. Next time, I’ll consider the relationship between shape and flex pattern.
Vail Ski School
Here’s a history lesson: When Norwegian farmers began running across snowy meadows on planks of wood, they quickly discovered that where the snow drifted deep, the plank flexed. When you jumped on the middle of the plank, it bowed downward into the snow. This meant that in order to push the ski forward, you had to push it up out of the hole it had made in the snow. That took a lot of work.
Some bright soul figured out that if you steamed the plank and bent it into a gentle arch (what we call camber), the skier’s weight would spread more evenly across the surface of the snow, and the skier’s weight would straighten out the camber instead of sinking into the snow. The loaded ski now made a more-or-less straight beam and could be pushed straight ahead. Running got a lot easier. If the camber were made high enough, you could carve the tip and tail a lot thinner, making the ends lighter and more supple. The ski became even easier to run on, and floated nicely over uneven snow.
By about 1840, in the Telemark region, local woodcarvers had figured out sidecut. Making the ski narrower in the middle helped the ski turn with better agility. But the narrower waist tended to sink deeper into the snow, so to avoid the original problem of the center sinking, the middle of the ski had to be made a bit thicker and the camber a bit higher. Thus, by trial and error, ski-makers learned the art of balancing flex pattern against sidecut and camber. Change any one element and you had to change the other two.
One more element entered into the balance: torsional stiffness. In a ski meant for running across uneven natural snow, you wanted a supple tip to float over and conform to the surface. But you needed strength, too — if the tip were too thin and soft it would break. As long as a ski was made from a single piece of wood, a clever solution was the ridge-top shape, carved with a central reinforcing rib standing above the top surface. The rib reinforced the ski’s beam flex (its stiffness in bending) but allowed it to twist a bit to absorb the impact of sastrugi, suncups, and the like.
After 1935, quality skis were laminated from a variety of tough hardwoods and lighter softwoods. As I mentioned yesterday, all alpine skis were still more or less the same shape, so the adustable elements were flex and weight. Now, by choosing and aligning the laminates, a skimaker could adjust the torsional stiffness more-or-less independently of the beam flex. The ability to do this took a quantum leap with the adoption of aluminum and fiberglass structures.
It became clear that racers wanted higher torsional stiffness than recreational skiers. For grip on ice, race skis were engineered with torsional stiff around 1.9 newton-meters per degree. This proved to be a practical limit: if the torque went much higher (some metal skis went to 2.5 nm/deg) they felt harsh and hooky, and had to be edge-bevelled pretty aggressively. Most recreational slaloms — bump skis, for instance — torqued at about 1.7 nm/deg. At 1.5 nm/deg and below you had forgiving intermediate skis. And a balance had to be found between torsion and beam flex: one factory called this the “torflex ratio.” A stiff beam flex, for a stronger, more precise skier, could use a stiffer torsion.
When “shaped” or deep-sidecut skis first appeared, it took a couple of years for engineers to figure out new flex patterns and torque ratios. Early shaped skis had a tendency to “hinge” in front of the binding, so they sort of plowed in deep snow — it was the original sinking-plank problem all over again. Compared to straight skis, it was found that shaped skis needed a longer stiff section in the middle and softer ends, and the progression of flex distribution had to be matched to the exaggeration of the sidecut. Similarly, torsion had to be softened a bit at the ends to soften the edge bite. Otherwise, the new wide shovels had a tendency to climb up the sides of moguls, and the new wide tails were reluctant to release at the end of the turn.
Balancing flex and torsion to sidecut is an art. It requires skill in adjusting core thickness, and clever choice of core laminates. Getting it wrong isn’t a disaster — a ski that feels a little harsh at the ends can usually be fixed with some smart tuning. But it’s so much more satisfying to get it right.
Vail Ski School
Jimmy Lillstrom stopped by over the weekend, in the course of his daily loop on the bicycle. Jim is a veteran ski industry marketing guy, a relic of the days when Head’s factory ruled North Boulder. He’s still a lean, mean cycling machine, carrying about 1% body fat.
But he doesn’t ski much anymore. A cycling crash years ago put a hairline crack in his femur, and in fixing it the surgeon took 3cm off the leg length. Since then he hasn’t felt comfortable in his normal boot size — everything seems to cant to one side. When he does ski, he uses an oversize boot and sacrifices control.
This is something that can be fixed. There’s a lot that can be fixed by a smart bootfitter. What can’t be fixed is skiing with good control and finesse in an oversized boot. Half the problems I see on the hill are due to skiers slopping around in boots just one size too big. A boot that’s too big is, by definition, too stiff. You won’t know it, because you can feel the ankle flexing inside the shell, but the shell itself doesn’t flex much and there’s a long delay before your muscular input is translated into pressure on the ski.
A big boot isn’t even warm. You wind up compensating for the slop by overtightening the instep buckle. That squashes the veins on the top of the foot, cutting off the return of blood from the foot to the heart and lungs. Blood pools in the toes and cools. The toes then freeze.
The solution is to get into the smallest shell that will take the length of your foot, and then do the work necessary, on the inner boot and inside the shell, to make it comfortable. If the shell fits properly, you can ski with the buckles pretty loose — on the first notch most of the time. The boots flex comfortably, you get a sensitive feel of what the ski is doing, and instant response to edging and pressure changes.
Getting that snug, comfortable fit starts with the smallest shell, then depends on an accurately shaped footbed (not the flat foam product packaged with the boot) and, possibly, a good aftermarket innerboot.
The innerboot is, in fact, the single most important piece of ski equipment. I can put my innerboot into nearly any boot shell of the right length and ski comfortably. I use the Zipfit innerboot, but there are some other good ones out there.
I told Lillstrom to call Sven Coomer, the Mahatma of ski boot design, and talk over the problem of differential leg length. We’ll get him fixed up so we can ski together.
Today is Sept. 7. It’s supposed to snow the next four days in Vail. I received an invitation today to ski at Copper with the PSIA Demo Team in October.
Time to wax the skis.
Old age and treachery will overcome youth and strength.
My dad was a superb semi-pro tennis player. It’s one of the reasons I became a skier.
The last time I tried to compete with him, he was about 50. I was 23.
I had speed and strength and endurance. He had wicked accuracy.
Dad could put his shots in the far corner from wherever I happened to be. I was forced to respond to each shot with some desperate defensive lob, aiming only roughly at the center of his court in hopes of saving the volley. Run ragged, I collapsed after the second set.
Dad, of course, didn’t have to run. His game was in his fingers and wrist. His expertise was subtle, and required relatively small movements of his forearm to guide the racquet. My game was gross, requiring that I heave 160 pounds of meat around the court.
Here’s the lesson for low-impact skiing: Use subtle moves inside the boot, and lateral gestures of the hands, to adjust the angle of the ski and thus the radius of the turn. Take advantage of terrain shape to guide your trajectory. You could waste a lot of energy lifting and throwing your body around, but why bother? The mountain will beat you after the second set.