Canting of Skis
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Note; Nothing has been changed in this booklet since 1994. Nothing really needs be changed in principle but I do intend to review it soon.
With a gap of eight years since writing appendix III all my experience has confirmed my views and several top skiers (BASI trainers etc) have become converts and use the KPS cant gauge for their groups.
In this booklet I have quoted Warren Witherell and his 1970 book "How the Racers Ski" on various occasions. It is therefore gratifying to find that his newly published book "The Athletic Skier" bases the whole of canting on the position of the knee. This is exactly the principle that I have been promoting since 1975 or so, and I have no doubt that it is correct and will, with the publicity generated by "The Athletic Skier", become the accepted measurement system in use at every ski shop. Warren Witherell has produced a gauge (page 174 "The Athletic Skier") suitable for shops. My own KPS gauge has the advantage of being truly portable – easily fitted in a suitcase without occupying any space (because it is flat) – and particularly quick to use in groups when one has become experienced in making a quick judgement of where the centre of the knee is.
To avoid one area of possible confusion it is worth noting that basing the measurement on the Knee Perpendicular above Ski system does not mean that the knee must be exactly at 0° . I recommend somewhere between 0° and 2° on the outside edges (see appendix III), and Warren Witherell recommends between 1° and 2° . More experience will soon clarify what is right for which skier in which conditions.
The only difference that I can find between Warren Witherell’s ideas and my own is that he finds it necessary to correct a significant number of people who are over-canted (i.e. negative or skiing on the inside edges). Almost all the corrections that I have done have been positive e.g. they are skiing on the outside edges (usually significantly so). This may be because he is dealing with racers and I am dealing with recreational skiers. No racer could be significantly over +3° ) on the outside edges. He couldn’t have progressed at all and would have given up and gone to play football instead!
If many racers really are on the inside edges until they are corrected, does this mean the following? Those beginners whose leg shape puts them initially onto the inside edge without having to angulate learn to use the inside edge more quickly and therefore progress to become racers. If so why don’t we give beginners a slight negative cant so that they learn more quickly? It has long been one of my suspicions that this would be so, but it remains to be tested!
What is Canting?
Figure 1 - Cant -The angle between the ski base and the leg.
The whole of this booklet is concerned with the angle of the surface of the ski in relation to the rest of the body as seen from the front. This is the angle between ski and leg in figure 1. The angle will be defined more exactly in the text but all reference to the "angle" or the "cant angle" is to the view from the front. There is no reference in this booklet to the view or angles as seen from the side. In order to avoid frequent repetition this is not restated in the text.
Since it is the angle of the ski on the snow that is the whole basis of skiing, the relation of the ski to the body or leg is of critical importance. Adjustment of this angle is referred to as canting. (It is also referred to as "wedging".)
This booklet describes a new and more objective method of measuring the cant angle than has been in use up to now.
The importance of canting has long been recognised. In the normal skiing stance the two skis should be flat on the snow, but "We Learned to Ski" published in 1974 quotes the American racing coach Warren Witherell as saying "that 80% of skiers stand on the outside or inside edges".
In 1974 or 1975 most London ski shops had machines to check whether a skier needed to cant (or wedge). The machines were designed to measure directly whether the skis would be flat on the snow in the normal skiing stance.
Figure 2 - Typical Cant Measuring Machine
Figure 2 shows such a machine. The skier would stand on two narrow plates which were free to tilt sideways. The deviation from the horizontal to which the top of each plate was set by the ski boot would be indicated by a pointer. That was then the correction required on each foot, by fitting appropriately shaped wedges under the bindings. This proved unsatisfactory for several reasons:
This last point is probably the main reason why canting has fallen into disrepute and is far less frequently used now than ten years ago.
However, this factor does not contradict the basic assumption that the two skis should be flat on the snow in the normal skiing stance.
This booklet provides further justification and evidence for this assumption, and also for the suggestion that most people need some adjustment to achieve this.
Ideally, this adjustment should be built into the boot such that everyone can adjust the boot for the shape of the lower leg when buying or hiring.
The emergence on the market of boots with a measure of canting adjustment creates a need to be able to identify which boots have a range of adjustment that accommodates the interested purchaser and also a need to be able to adjust such boots accurately. Use of the old canting machine will still suffer from the problem of subjective readings and ability to adjust the stance.
This booklet explains a simple and effective method of achieving the correct adjustment for each individual.
The idea that the skis should be flat on the snow in the normal skiing position suggests that the knee should be approximately above the ski. The ski boot is therefore designed to achieve this.
However, the angle of the boot is defined only by the shape of the part of the lower leg and foot that it clamps onto. This part of the shin is far from straight as shown in Figure 3.
Figure 3 - Lower leg is not straight
The line of action of the lower leg is from the centre of the knee joint to the centre of the ankle joint. This line is shown in the diagram. Between the joints the bones and muscles are curved and offset to the outside. This has probably evolved to allow clearance for the other foot in the walking or running stride. It is most pronounced just above the ankle joint in the critical area where the shank of the ski boot clamps onto the leg.
All boots must therefore have a built-in angle to compensate for this effect. This can be seen by looking at any ski boot from the rear while it is standing on a table (Figure 4).
Figure 4 - Ski boot from rear
When the angle is chosen in the design of the ski boot it is assumed that the variation between people is small enough for them to compensate easily.
Warren Witherell points this out in "How the Racers Ski". To the question "Why do so many skiers need wedges?", he answered;
"Human leg bones are as varied in shape as human noses. Each person’s leg and ankle structure produces a slightly different angle for the shin bone to rise from the floor in a natural stance."
All of this produces a totally random variation in the angle at which the ski is attached to different people. This must be important in skiing.
The angle of the ski on the snow is the whole basis of skiing. This angle is controlled by the lower leg of the skier, but we have seen that variation in leg shape introduces a random variation. This must be important and should be compensated for in the boot, but how should this compensation be done? What relation of ski to lower leg should we aim at?
At the initial stage of such an inquiry it is normal engineering practice to return to first principles in order to develop a basic theory. This basic theory should be simple and can then be tested and modified by experience. The conclusion from various analyses and from various experiments is as follows:
"The perpendicular from the centre of the running surface of the ski should pass through the centre of the knee joint." (Figure 5)
The reasons for this conclusion are as follows:
In a modern ski boot the ankle is more
or less rigid sideways. The knee should really be looked upon as a pin joint.
It is not really designed for applying a sideways force at the foot. This can
be checked by sitting on one chair and placing the feet on the ground outside
the legs of another chair placed in front of you. With the lower leg vertical
and the knee bent through 90° you can apply an inward force with both feet, but
not a large force, and maintaining the force for only 20 seconds or so makes it
clear that equipment should not be designed to require the skier to apply such
a force continuously. This means that the knee is not designed to cope with a
force from the ski where the line of action lies outside the knee. Hence the
forces on the knee should pass through the knee, preferably near the centre. In
addition, the force from the ski will be approximately perpendicular to the
running surface of the ski in contact with the snow.
Figure 5. Correct Canting
Hence the perpendicular from the centre of the running surface of the ski should pass through the centre of the knee joint.
Figure 7 - Straight running. Either leg seen from front
All of these arguments support the statement that:
"The perpendicular through the centre of the running surface of the ski should pass through the centre of the knee joint."
It is necessary to have a measurement system to define and compare deviations from this ideal situation. I suggest the following definition:
"The KPS (Knee Perpendicular above Ski) cant angle of a particular combination of boot and lower leg is the angle, seen from the front, between the perpendicular through the centre of the running surface of the ski and the line from this centre to the centre of the knee joint.
Where the perpendicular lies inside the centre of the knee joint the angle is negative; where outside, the angle is positive."
The angle obviously applies not to a boot, not to a person’s leg, but only to a particular combination and may be different for the right and left leg in one pair of boots.
Figure 8 shows an example of a leg/boot combination that
would have a KPS cant angle of +8° . The perpendicular from the centre of the
ski passes outside the knee joint and is at an angle of 8° from the line from
the centre of the knee to the centre of the ski.
Figure 8 - Left leg with +8° KPS cant angle
Measurement of the KPS cant angle is simple.
Figure 9 - KPS Cant Gauge (patent applied for)
It is only necessary to locate a gauge on the flat under-surface of the boot, or the running surface of the ski, and for a scale in degrees to be in front of the knee such that the KPS cant angle can be read off.
The simplest form of gauge consists of a flat sheet of plastic shaped as shown in Figure 9 with a hole for the boot and a scale on the top near the knee.
The reading given by this gauge will be generally in line with that given by the older cant measuring machines (see figure 2). However, the KPS cant gauge will give an accurate, non-subjective reading which is not prone to errors and is more correct in theory.
To measure the cant angle of your right boot plus lower leg combination, proceed as follows:
This is the KPS cant angle for that combination of boot and lower leg.
Since the bottom of the cant gauge acts as a pivot it is not necessary for the lower leg to be vertical. The reading remains the same when the knee is moved from side to side.
The reading should be taken to the nearest whole degree.
Where the zero line of the gauge lies outside the centre of the knee, the angle for that leg/boot combination is positive. If the zero degree line on the gauge lies inside the knee, the angle for that leg/boot combination is negative (this is very rare).
The cant gauge can be used in exactly the same way with the ski attached to the boot. The width of the ski is approximately the same as the width of the underside of the boot so it will locate on the measuring surface of the gauge in exactly the same way. (Compact skis being wider, may not fit between the edges of the gauge surface.)
Figure 8 shows a left leg with a KPS cant angle of +8° . Note how far the perpendicular is outside the knee as a result of 8° .
When skiing in a turn the forces on the ski will distort the boot and increase this angle greatly. This is why measurement must always be done without sideways force on the boot.
To ensure accuracy when using the KPS cant gauge, the following points should be noted:
Confirmation, Conclusions and Advice
The next step in this engineering study of canting is some confirmation of the theoretical predictions.
In about 1975 I was able to check about 20 people including at least 10 very good skiers, several top grass skiers, several top freestylers, ex-junior racers, several BASI qualified and 1 BASI 1.
All the good skiers got a reading of less than +1° , all but 1 being between 0° and +1° . One had a negative reading: That is the perpendicular was inside the centre of the knee.
The less good skiers varied by several degrees. My own reading was +4° on each leg. Anyone above +5° was always a poor skier. Older boots, for instance the leather clip generation, were always +5° or more.
I looked upon this one fairly limited measurement as adequate confirmation and adjusted my own boots to 0° .
The 20 or 30 measurements that I have made subsequently have confirmed my conclusions. The appendix contains a selection of case histories.
The limited number of measurements and corrections that I have been able to do are only a first step towards a full understanding of canting.
However, in the absence of any contrary evidence or proposal, I believe the evidence is sufficiently substantial to confirm the general rule:
"In a lateral plane the perpendicular through the centre of the running surface of the ski should pass through the centre of the knee."
Two important questions arise at this point:
Warren Witherell said, "for racers I insist on wedging to 0.5° accuracy". This was based on wide experience and I am sure he will be proved right. My own limited experience only allows me to suggest working to an accuracy of about 2° . In addition, I do not know the exact relationship between the old rule "both skis flat in the normal stance" and my new rule, the KPS, or Knee Perpendicular above Ski rule. I have found measurements of cant by the old machines to be subjective and inaccurate but I believe that the two rules are the same within approximately 2° .
Based on this accuracy figure of 2° and the experience available, the following rules can be listed:
Adjustment – Ideal
The subject of adjustment must be divided into two parts – ideal and "what to do now", because we are not at present in an ideal situation.
Ideally there should be adequate adjustment in all ski boots to cover the variation between people. At the time of purchase or hire, the boot would be set to the correct cant angle.
The foot and the part of the boot surrounding the foot does not need to adjust. As shown in Figure 3. It is the lower leg above the ankle joint that varies and it is this part of the boot, the shank of the boot, that needs to be adjusted in its relation to the lower part of the boot. It is possible that this can be done relatively easily at the hinges by adjusting the outer one up or down.
This is exactly the mechanism that is available in several ski boots on the market today. Unfortunately the range of adjustment is usually only 4° or 5° and this is centred on the average for non-adjustable boots. Hence the person who is most in need of adjustment can make use of only 2° , while he might need 10° .
One such 1982 boot that I tried was adjustable to KPS cant readings on my foot of +5° to +9° . I could not adjust to 0° using the cant adjustment provided.
The range of adjustment necessary is, I believe, at least 10° and this should not be centred on what is normal for a non-adjustable boot. The full 10° of compensation should be available in the direction that will bring someone who had a +10° KPS cant reading as defined earlier to the 0° position.
When this adjustment is routinely available on all boots it will be normal to "set" the boot/leg combination to the correct angle in the shop. A skier may find that he likes to ski on +2° or -1° and will be able to set any boot to that angle when it is on his foot by using the simple gauge. A racer may also like to adjust his boots to different settings for different races.
Adjustment – What to do now
This section is really the advice to the individual on what to do having measured the cant angle of his boot/leg combination.
The present situation is not ideal. When the full required range of adjustment is available in the boots, there will also be a good body of advice available on the exact settings to aim at and what deviation is important.
For the moment, advice can only be based on the theory and the limited practical experience described earlier. However, in the absence of anything more comprehensive the following should help many skiers and will lead eventually to the ideal situation.
Having made the measurements, the next question is whether to make any adjustment.
First a few words of caution:
The next problem is how to implement the change. There are 6 methods available:
1 – 5 above apply to the boot, but the total correction even using several of these is still only 7° or so. The alternative is 6.
Wedges have been used for many years by some people, but great care should be taken to ensure that the bindings and ski brakes still work correctly, particularly if the wedge angle is larger than about 6° .
For those whose KPS cant reading is greater than +6° or so, wedging is really the only method available, but it may lead to discomfort because the footbed in the boot will not be horizontal. Footbed insets may help in improving comfort but they will not influence the cant angle (as pointed out by Witherell).
The direction in which any correction must be applied has not been explained in detail. This is best determined by thinking carefully about the situation. With the knee directly above the ski the adjustment must aim to put the running surface of the ski flat onto the snow.
In fact, I believe that almost all measurements will yield positive values of KPS cant angle and wedges for instance will have the thicker edge on the inside of the ski
There is as yet no generally accepted rule on canting. I hope that this hypothesis will lead to such a rule and general understanding. Within the simple general rule the more complicated detail must be incorporated. The following are some general observations but none of these have yet been adequately studied.
Most good skiers will have KPS cant readings in the same range. This is probably due mainly to "the survival of the fittest". If they didn’t lie close to the centre of the range they would have found learning skiing difficult and would have gone back to football!
However, the setting chosen by the boot manufacturers is probably not centred on the ideal. I have suggested that the ideal is close to 0° but people can certainly ski well at +7° , particularly if they are good enough to ski entirely on the outer ski. I don’t believe that anyone could ski at -7° and probably not even at -3° . This is because sideslip, and therefore edge control, would be impossible for the reason given in Chapter 2, No 2.
A boot that was designed to have the centre of the range at 0° would be rejected by the very best skiers, those who would land up at -5° in this boot but have about 0° in most boots.
Hence, boots are designed so that all skiers will be on the positive side of the ideal and only a small proportion will be very close to it. I suspect that the vast majority, even of good skiers, would benefit from some degree of adjustment.
Having to design the boot so that no one is on the wrong side of the ideal means that everyone is on the other side of the ideal.
There is another forcing factor in boot design. It was reported in one American skiing magazine that a well-known Swedish racer cants in order to put the skis onto the outer edge. This seems to mean that he aims at a KPS cant angle somewhere between +3° and +6° . I have also read that many Swedish and other slalom skiers have followed suit. This may be associated with the Slalom and GS technique of initiating the step turn very early by putting the weight onto the outside edge of that inside ski (the edge nearest the gate) at a very early stage in the turn.
This may or may not be relevant to the average skier who need stability and edge control above all and of course this adjustment for slalom might be totally unsuitable for downhill because of reason 4, Chapter 2.
Techniques and adjustments used by racers are very quickly incorporated into recreational ski equipment. This demand by top racers for a more positive KPS cant angle may be why boots seem to have been designed to give a more positive angle by 3° or 4° over the past 8 years or so.
My 1976 boots require adjustment by 4° , but my 1982-3 boots require 7° . This may well mean that most good skiers would now have readings of 3° - 4° or so, instead of the 0° - 1° measured in 1975-6.
This "fashion" change in cant angles of ski boots was noted also in "How the Racers Ski". "Prior to 1972, most ski boots were made so that nearly all skiers stood naturally on their outside edges. Responding to the publicity given to wedges in 1970 and 1971, the boot makers built a more severe outward cant into their 1972 boots. The result was that many more people – at least a third of the 500 racers I tested – stand naturally on their inside edges in the new boots". (Warren Witherell)
As I have suggested, being too much on the inside edge, a negative KPS angle, makes a ski very difficult to control and I suspect that this is why less outward cant has been built into the boots since that time – to the disadvantage of those, like myself, who were on their outside edges even in the 1972 boots!
The purchase of new boots in The Alps in January 1983 forced me to ski for 3 weeks at +7° , having skied at +1° to +2° for 6 – 8 years, and was therefore a good opportunity for comparison.
I was instructing over much of the 3 weeks and had no difficulty in demonstrating the basic manoeuvres or those up to a good parallel turn. The main difficulty was with quick turns. I was unable to take a mogul field fast and continuously. I was unable to change edge quickly and set the new edge.
I adjusted the boots to 0° for the 1983-4 season. The difference was very marked and confirmed by hypothesis that the ideal setting is close to 0° . There were no disadvantages and clear advantages in all types of skiing.
One difference may be of particular note. When skiing at +7° I experienced, for the first time ever, frequent pain from the medial ligament of one knee. This was probably due to reason 7 in Chapter 2. On changing back to 0° this was totally absent. Skiing at a positive KPS angle will mean that the forces on the knee do not pass close to the centre of the knee and result in tension in the medial ligament. I suspect that this may be associated with some knee problems in skiing.
In the natural stance the lower leg is approximately vertical. Because of this the KPS canting rule defined in this booklet will give approximately the same results as the old rule that the skis should be flat in the natural stance.
However, the theory behind the KPS rule is different. It is related to the mechanical behaviour of the unit formed by ski plus boot plus lower leg. This means for example that knockneedness is not important. Only the shape of the lower leg and the resultant KPS cant angle need be considered.
The KPS rule has a sound theoretical basis. It is supported by practical experience. It leads to a simple form of gauge which gives an accurate reading which is not influenced either by the measurer or by variations in the stance of the subject. The gauge is portable and inexpensive, allowing use by racers and recreational skiers.
With the gauge it should be possible to build up a body of experience which will allow ideal settings to be used with the appropriate small variations for skiing standard, age, sex, type of race discipline, type of ski and any other factor that is found to be important.
Case 1 – The Author
I had suspected the problem for a long time. I had even tried to correct, but subjectively I thought that only one foot needed correction and so had probably made myself even more one-sided than previously.
I visited the London shops that had canting machines in 1973 or 1974 and none of the operators said I needed to cant.
As I stood on the machines it was obvious that the answer just depended upon how I stood and where I put my knees.
Following my own investigations I corrected by 4° on each foot. I find this a great help in all types of skiing.
A chalet girl in Selva who was a water ski champion but despite determination and balance was having great trouble with snow.
Her skis were obviously on the outside edges all the time and when measured she was +7° on one leg and +10° on the other. This was corrected with wooden wedges under the bindings and in the opinion of the group I was with – all good skiers – she was immediately better and in the course of 1 day she improved dramatically.
An enthusiastic but mediocre middle-aged skier whose skis were visibly on their outer edges.
Measurement gave +1° on the right leg but +7° on the left. This corresponded to exactly what he had thought for years but had never been able to prove.
Candidate on 1980 BASI course at Flaine. Obviously having to make large compensations in style. Measurement gave +10° . (Failed course – refused to correct.)
Athletic boy of 14 or so who had skied for 3 to 4 weeks and was progressing well but already having to compensate excessively. His Waterloo came on a day of new snow. He couldn’t stop his skis diverging. Measurement gave +7° which I corrected to 0. Within a day his style was much more normal.
Medium to advanced skier having problems getting edge change correct in 360° turns on gentle slopes. Corrected cant by +2° approximately and found edge change much easier. (Note: The implication of this booklet for the freestyler must be obvious.)
"How the Racers Ski" by Warren Witherell. Pub: W W Horton & Co 1972
"We Learned to Ski" by Harold Evans, Brian Jackson and Mark Ottoway. Pub: 1974
Appendix II – written August 1985
Appendix III – written October 1986