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This analysis is motivated by a desire to find the top speed attainable in inline skating and is based in part on an excellent introductory series of articles in SpeedSkating Times (SST) running from 1994 through 1995. This series was written by John Banks and was entitled "Physics 101...or why you probably won't ever skate 50mph." My reading of those articles leads me to think that he felt that the top speed was set by the large wind drag force balanced by a propulsive skating force or thrust which was limited by a fundamental skating efficiency in the neighborhood of 10%.
As I recall, the top speed (level track, no wind) obtained by inline skaters is about 30mph whereas for cyclists it is about 40 mph. If we accept the idea that the wind drag force varies as velocity squared (* see footnote) then at their top speeds cyclists develop (40/30)**2 = 1.8 times the thrust of the skater in order to maintain their top speed against wind drag. I find it extremely difficult to reconcile this conclusion with the claim that skating has an efficiency of 8-12% at top speed and believe that this efficiency conclusion mis-states the situation. The SST series was entirely based on the classical left-right leg stroke of ice-skating and this analysis is largely also based on that for simplicity. This analysis does not seriously take into account thrust losses from bearing friction, wheel friction with the ground, wheel deformation, and wheel angular momentum.
The first figure below on the left sets up the scenario. The skater wishes to move forward in the direction of the velocity vector and plans to push sideways--- right with the right leg and left with the left leg.
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The figure on the right shows more detail of the right skate and the forces. The skate is inclined outward at the angle "Angle" relative to the forward velocity vector. The skater pushes outward with the force vector F which I have broken into two pieces: F1 and F2. I did not see this force decomposition in the SST series. F1 is perpendicular to the skate direction of motion and grips the ground strongly. The ground's reaction to F1 pushes the skater left and forward relative to the ground. I identify F1 with the "Duckwalk" motion where one walks or runs on his skates. This is highly effective at low speed and is great for the start. It also allows the skater to remain balanced over his skates at higher speed. The other force F2 propels the skate itself right and forward relative to the ground. This is the force which I identify with serious speedskating. The real bind comes in at high speed where the skate angle relative to the Velocity becomes very small-- a few degrees. As the forward thrust is | F2| =| F|*sin(Angle), it is easy to see that the forward thrust suffers a serious setback at small angle, i.e. high speed. The SST article interprets this as meaning that the efficiency becomes very small (** see footnote). This may be true in a popular sense but it is incorrrect in an engineering sense: for a good skater the product F2*distance_forward is still about equal to F*distance_sideways so that the work done is still highly efficient. The problem is that the skater is not strong enough to make the skate move far enough to do the needed work. In other words, the force he needs to generate becomes ever larger as the angle becomes small and eventually exceeds his strength threshold. In bicycle terms the skater is in too high a gear. He needs to lower the gear or increase the mechanical advantage. The skater does this by increasing his stroke rate which increases the skate angle "Angle" and allows him to skate with less applied force but at the cost of increased frequency of stroking.
The cyclist faces nearly identical problems with strength, mechanical advantage, and wind drag. So why are cyclists faster than skaters and how do they generate the 1.8 x larger thrust discussed earlier? In my opinion the answer lies mainly in duty cycle. The classical skater pushes with only one leg at a time whereas cyclists have pedal clips which fasten their boots to the pedals allowing them to simultaneously push with one leg and pull with the other. Therefore they can generate about twice the force of a skater and operate at 100% duty cycle.
The "Chad" or double-push inline skating technique moves in the direction of getting both legs involved simultaneously increasing the force level and the duty cycle. Can it be developed to the point where skaters move as fast as cyclists? Note added 6/16/97. Having analyzed the double push now on another page I believe that any remaining differences between cyclist's and skaters speeds are due to the larger rolling resistance of skate wheels. Hopefully I can explore the wheel issue in detail before the summer is over. The newly awarded patent for pneumatic inline skate wheels (Tom Peterson, Hyper Corporation) may take care of much of that issue.