Your comments yesterday got me thinking. Your issue isn’t with going straight, but with being on edge, according to what you said. Now, when skiing, the edges are used to turn, so what I think we should do, in the same way I tried to break down the theory into simple, bite-sized chunks, I shall attempt to do the same today, and hopefully my understanding will increase.
There is basically only one way to turn. (Now there’s a bold statement that needs backing up.) What do I mean? Well, this is the only way to turn: have one side move forward a different distance to the other.
Here are three examples:
1.Stand at the centre of a child’s roundabout, i.e. one foot either side of the turning axis. Get someone to turn the roundabout through 90 degrees. What happens? One foot travels forward, and the other travels backward by the same distance. You have made a turn.
2.If it is possible, on the same roundabout, stand with one foot on the turning axis. Again, ask your assistant to turn the roundabout through 90 degrees. And again, examine the outcome. One foot has not moved forward or backward. The other has moved a considerable distance.
3.This may be more difficult to see, and to measure really requires using mathematics. Stand in a natural stance near the edge of the roundabout, facing tangentially (i.e. not looking out to the edge, or in to the centre, but facing the direction of turning). Measure the distance from the turning axis to your left foot (Rl), and then again to your right foot (Rr). Even if your feet are tight together in an unnatural stance, there is still a difference in distance between the feet. During a 90 degree turn, the difference between the distances will be: (Rr-Rl)* Pi/2, i.e. 1.57*stance gap. It doesn’t matter the size of the roundabout, the difference in distance will always be the same. E.g. if your left foot travels 5 metres, and your right foot is 20cm from your left, your right foot will travel 5.31m.
For an object with width > 0, turning must consist of one or more of the above.
Do you agree?
Now, when walking, turning can easily consist of any of the three above, although we rarely stop and make a jump/twist turn as in 1! Yesterday, I talked about running more than walking, because the speed and impact loads were greater, and so certain aspects were more exaggerated than you’d find when walking. Likewise today, if we consider running, an athlete does not turn using 1. or 2., but only 3. To use 1. would require him stopping running to make the turn. To use 2. would twist his ankle. The only option is 3. to allow one leg to travel further than the other.
Again, I trust you are in agreement.
At higher speeds, how does the runner achieve this sort of turning? Again, as far as I can see, there are three ways:
1.Change his stride pattern so the outside leg takes bigger strides, and the inside one takes smaller. Perhaps this is done at slow speeds or on tight turns, but it breaks the rhythm, and would unbalance the runner at speed
2.Put more weight on his outside foot. Now, due to centrifugal forces, this is more natural. At speed, his body will want to go straight on while he tries to turn, so there will be a greater force from his body acting through his outer foot. When this happens, it is almost as if 1. is occurring. The reduced force on the inside gives reduced grip and reduced power from that leg, so less distance is covered. This is one of the principles at work when a car turns a corner – you feel the car leaning out, and inside the car, you get pushed to the outside of the turn.
3.In a sense, the third way is “cheating”, because, instead of changing the runner, you change the bend. Put a bank on it. (and I don’t mean one with an ATM!). This allows the runner to continue around the bend without having to worry about changing weight or stride. And for this, I’ll give another car example: which is easier? Formula 1 or Indy Car? I would argue that Indie Car is easier, due to the banked circuits. The drivers can keep the speed up around a bend, while in F1, they have to back off the power to get around a flat, or slightly banked bend. If the driver doesn’t have to slow down, then there are less additional forces acting on him and the car while turning. And less forces = less stress on the frame.
Again, hopefully you’ll agree with my summary of how to take a bend. In skiing, until about 10 years ago, the technique involved a mixture of 2 and 3. There was a shift of weight and leaning onto an edge, which basically created the effect of a slightly banked turn. Then along came skis with increased side-cuts. The effect of the side cut was to give the ski more of a natural ability to turn, even before putting any pressure on it to flex it. This means the ski effectively adds to the banking of the turn. Before modern skis with their side-cuts came along, skiing was more akin to F1, requiring weight transfer as a major part of the turn, yet now it is more like Indy Car, maintaining speed through the turn by using the skis ability to carve.
So, as I see it, the easiest way to make a turn is to allow one side to travel further than the other, and to do this on a banked turn. Or, to put it another way, let the skis carve their way around the turn while not putting a large proportion of the weight/pressure onto one ski or the other.
As an aside, the first part of my comments about distance travelled does lead on to ski design. They would point to the ultimate ski design for turning on piste would be one where the outside edge of the ski encouraged tighter turning, while the inside edge was for longer radius turns. What I mean is, when turning to the left, you are on the outside edge of your left ski, and the inside edge of your right, and the right needs to travel around a wider curve than the left. Perhaps you need to have the inside edges designed to go faster as well, I’m not sure on that one, and I don’t have any of my university books with me to work it out, but this is a complete aside, and not the main point of my post