You recently posted this graph on another thread which is clearly showing the slowing effect of the turns in a track race on speed.
A year or so ago a national track coach got PowerCranks for his team and his stated hope was that with them he hoped that the team members would be able to maintain speed on the curves.
My question is this. Is it better for the race to hold back a little on the straights so as to be able to increase effort on the turns to maintain a constant speed or to ride at “constant” power (I doubt the power is really constant and the rider probably increases some coming out of the turn to bring speed back up, but I don’t know what really happens) and accept such speed variations between the turns and the straights? Which is the better strategy and how much difference does it make?
…his stated hope was that with them he hoped that the team members would be able to maintain speed on the curves.
Then he forgot to check the physics involved in turning KE pointing north and making it go south.
But, you did that already, right…? Would you summarize the formulas for us real quick?
Let me rephrase the question for those unable to understand the nuances. For a track race on an oval track, is it theoretically better to try to ride at a constant speed or a constant power and why?
How would PowerCranks aid in maintaining a constant speed in the turns?
Regarding #1, Did I spell Dr. Coggan’s name wrong again? (edit: I see, “an question” - the hazards of the internet, at least slowtwitch has an editor. )
Regarding #2, I don’t know? I suspect he hoped that training with them would give them enough reserve to increase power during the turns. I questioned the supposition also, but it got me thinking. If one has that increased ability, my question is, is it better to try to maintain speed during the turn or to use that increased ability during the entire race?
As a former track runner(who finds himself on a 100 meter track on occasion now) I’ve got to believe it would be almost impossible to maintain, or increase speed on the curved section of the track, without a very large increase in power, which would be better put to use on the straight sections. Having watched Alan Webb run a 1600 last year, there may be something to what is basically smoothing the curve to extend the straight if that makes any sense at all. I don’t know if that helps with the question- but I would have to believe you are loosing a lot trying to maintain speed, where as maintaining power would make sense, its just going to not keep the speed do to the turning and leaning actions that occur.
As a former track runner(who finds himself on a 100 meter track on occasion now) I’ve got to believe it would be almost impossible to maintain, or increase speed on the curved section of the track, without a very large increase in power, which would be better put to use on the straight sections. Having watched Alan Webb run a 1600 last year, there may be something to what is basically smoothing the curve to extend the straight if that makes any sense at all. I don’t know if that helps with the question- but I would have to believe you are loosing a lot trying to maintain speed, where as maintaining power would make sense, its just going to not keep the speed do to the turning and leaning actions that occur.
Steve
I think running is a different issue than track racing since stride length changes on the curve between the inside and outside leg. Maintaining speed on the curve and good form may not be possible regardless of the energy cost. That is not an issue on a track bike. The question is simply what is the best use of the available energy. We know how most people actually race but it does not necessarily follow that such a strategy is the best strategy.
Ahh, I wasn’t even thinking cycling for some reason. Wow, I feel kinda like a dunce… But even in cycling wouldn’t you have (for lack of a better word) Slippage up the track so you would be losing some speed and power on the bike to that force trying to push the bike to the outside? I think thats where the loss occurs, with you introducing another force to it.
Ahh, I wasn’t even thinking cycling for some reason. Wow, I feel kinda like a dunce… But even in cycling wouldn’t you have (for lack of a better word) Slippage up the track so you would be losing some speed and power on the bike to that force trying to push the bike to the outside? I think thats where the loss occurs, with you introducing another force to it.
The tracks are banked.
But even in cycling wouldn’t you have (for lack of a better word) Slippage up the track so you would be losing some speed and power on the bike to that force trying to push the bike to the outside? I think thats where the loss occurs, with you introducing another force to it.
Frank is correct in saying that the turns are banked so as to reduce the force of friction required between the tires and track surface to keep the bike from slipping in the turn. However, for a given turn radius and bank angle, there is only one speed which an object can travel the turn without any force of friction impeding the objects upward or downward motion around the turn (hence the yellow sign recommended speeds for banked highways). A small amount of friction tugging at the bike will be present at any other than this “optimal” speed and will, perhaps, cause a small decrease in speed - not so sure about that but…
After thinking about it for some time, my gut tells me that the reduction in speed around the curve is largely caused by an increase in rolling resistance due to the drastic increase in the normal force of the bike-rider object from the track surface. This increase in normal force is, of course, due to the centripetal force required to change the direction of inertia (from north to south as Ashburn said earlier).
On the flats the normal force is equal to the (Mass-of-bike-plus-rider)(gravity)
On the turns the normal force is equal to (Mass-of-bike-plus-rider)(gravity) + A Component of the centripetal force.
The normal force is the force that compresses the tire and dictates the size of the “Contact patch”
This extra force in the turns will cause a larger than normal surface area of the tire’s “Contact patch” and a greater amount of tire bending…
(thanks Rick!)
Don’t really see how Powercranks would change any of this.
Is it better for the race to hold back a little on the straights so as to be able to increase effort on the turns to maintain a constant speed or to ride at “constant” power (I doubt the power is really constant and the rider probably increases some coming out of the turn to bring speed back up, but I don’t know what really happens) and accept such speed variations between the turns and the straights? Which is the better strategy and how much difference does it make?
From a physical (physics) perspective, it’s essentially a wash. The same is true from a physiological perspective, except that it becomes increasing difficult to ‘lift’ one’s effort during the transition from turn to straight as fatigue develops (e.g., during a pursuit). From that perspective, then, riders may be able to go slightly faster if they try to “power the turns and float the straights” instead of “powering the straights and floating the turns”. This will only be true, however, if the differing strategies result in significant differences in average power output.
Of course! When you bank the bike, you decrease the effective wheel circumference by riding on the “sidewall” of the tire, affecting cadence, angular velocity of the wheel, and aero drag of the wheel.
Now, with Power Cranks, the rider should be able to drag both pedals like training wheels, keeping the tires normal to the road and eliminating this effect.
Of course! When you bank the bike, you decrease the effective wheel circumference by riding on the “sidewall” of the tire, affecting cadence, moment of inertia of the wheel, and aero drag of the wheel.
It’s more (far more) due to the fact that as you lean over, your center of resistance travels a shorter distance than the radius of the turn, forcing the wheels to speed up. (Think of the circus stunt with the motorcyclist(s) riding 'round and 'round in a spherical iron cage with the beautiful woman in the middle…the wheels of the motorcycle travel a great distance, but the rider’s head is pratically stationary.)
Is it better for the race to hold back a little on the straights so as to be able to increase effort on the turns to maintain a constant speed or to ride at “constant” power (I doubt the power is really constant and the rider probably increases some coming out of the turn to bring speed back up, but I don’t know what really happens) and accept such speed variations between the turns and the straights? Which is the better strategy and how much difference does it make?
From a physical (physics) perspective, it’s essentially a wash. The same is true from a physiological perspective, except that it becomes increasing difficult to ‘lift’ one’s effort during the transition from turn to straight as fatigue develops (e.g., during a pursuit). From that perspective, then, riders may be able to go slightly faster if they try to “power the turns and float the straights” instead of “powering the straights and floating the turns”. This will only be true, however, if the differing strategies result in significant differences in average power output.
Well, since these races are timed to the .001 sec it seems that there might be a possibility that a small advantage one way or the other might be a significant racing advantage if everyone else is using the lesser technique. It may not make any difference as to which racing technique is used if training with the PC’s allow the riders to significantly improve their average power output despite the reason the coach thought they may be useful. Anyhow, we should begin to see if there is anything to this in LA soon. This will be the first WC for this team since they started training on the product. I hope to find out if he has found any advantage to racing this way or if he has abandoned it to what is normally done.
It’s more (far more) due to the fact that as you lean over, your center of resistance travels a shorter distance than the radius of the turn, forcing the wheels to speed up. (Think of the circus stunt with the motorcyclist(s) riding 'round and 'round in a spherical iron cage with the beautiful woman in the middle…the wheels of the motorcycle travel a great distance, but the rider’s head is pratically stationary.)
Very interesting. As I said, it was only my gut that led me down that path and my gut is usually wrong when it comes to mechanics. I was using the assumption of a point mass which is how I always thought about these kinds of problems in physics. In actual practice things are quite a lot more complicated.
By “center of resistance” do you mean center of mass? I’m thinking of it as the inertial resistance to the acceleration.
So the bike-rider system actually speeds up in the turns and in shorter radius turns the acceleration is greater?
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