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Sprinting technique
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Gary Kunstmann
Aug 2, 2012, 11:04:49 AM8/2/12
to
Been meaning to query this group on subject information. Noticed that
field sprints result in extreme back/forth leaning of bike frames as
riders attempt to increase the power applied to crank. Also noticed
similar techniques in time trials to a lesser degree and even road
riding. Understand the purpose and concept, but the technique also
seems to result in the wheel tracks following a zig-zag path rather than
the shorter straight line distance to the finish line.
Has anyone done the math to prove that the added power applied to the
crank results in a decrease in time to the finish line that is greater
than the loss of time by riding a zig-zag path to the finish line?
Would not the result of the extreme leaning be better if the zig-zagging
was minimized, or even eliminated?
field sprints result in extreme back/forth leaning of bike frames as
riders attempt to increase the power applied to crank. Also noticed
similar techniques in time trials to a lesser degree and even road
riding. Understand the purpose and concept, but the technique also
seems to result in the wheel tracks following a zig-zag path rather than
the shorter straight line distance to the finish line.
Has anyone done the math to prove that the added power applied to the
crank results in a decrease in time to the finish line that is greater
than the loss of time by riding a zig-zag path to the finish line?
Would not the result of the extreme leaning be better if the zig-zagging
was minimized, or even eliminated?
DirtRoadie
Aug 2, 2012, 12:05:43 PM8/2/12
to
help toward envisioning the complete picture.
Note that just because the wheels track a sinuous path does not
necessarily mean the rider's center of mass does. In fact the wheels
themselves don't even follow the same path.
So "loss of time by riding a zig-zag path" is at least partially
illusory. Not saying it doesn't exist just that it is probably much
less than casual observation might suggest. Watch, for example, a
rier's hips.
http://www.youtube.com/watch?v=SAv_0km_pls
DR
PS In ski racing a racer feet often go around a pole while the racer's
body mows it over.
frkr...@gmail.com
Aug 2, 2012, 1:29:30 PM8/2/12
to
Jobst frequently referred to "cosine error," i.e. that the cosine of a small angle is very close to 1. It applies here in that the angular deviation doesn't add much extra distance at all.
- Frank Krygowski
DirtRoadie
Aug 2, 2012, 2:19:33 PM8/2/12
to
On Aug 2, 11:29 am, frkry...@gmail.com wrote:
> On Thursday, August 2, 2012 11:04:49 AM UTC-4, Gary Kunstmann wrote:
> > Been meaning to query this group on subject information. Noticed that
>
> > field sprints result in extreme back/forth leaning of bike frames as
>
> > riders attempt to increase the power applied to crank. Also noticed
>
> > similar techniques in time trials to a lesser degree and even road
>
> > riding. Understand the purpose and concept, but the technique also
>
> > seems to result in the wheel tracks following a zig-zag path rather than
>
> > the shorter straight line distance to the finish line.
>
> > Has anyone done the math to prove that the added power applied to the
>
> > crank results in a decrease in time to the finish line that is greater
>
> > than the loss of time by riding a zig-zag path to the finish line?
>
> > Would not the result of the extreme leaning be better if the zig-zagging
>
> > was minimized, or even eliminated?
>
> I think the zig-zagging is not very pronounced.
Those who have actually ridden in such situations (or had their front
> On Thursday, August 2, 2012 11:04:49 AM UTC-4, Gary Kunstmann wrote:
> > Been meaning to query this group on subject information. Noticed that
>
> > field sprints result in extreme back/forth leaning of bike frames as
>
> > riders attempt to increase the power applied to crank. Also noticed
>
> > similar techniques in time trials to a lesser degree and even road
>
> > riding. Understand the purpose and concept, but the technique also
>
> > seems to result in the wheel tracks following a zig-zag path rather than
>
> > the shorter straight line distance to the finish line.
>
> > Has anyone done the math to prove that the added power applied to the
>
> > crank results in a decrease in time to the finish line that is greater
>
> > than the loss of time by riding a zig-zag path to the finish line?
>
> > Would not the result of the extreme leaning be better if the zig-zagging
>
> > was minimized, or even eliminated?
>
> I think the zig-zagging is not very pronounced.
wheel taken out by a zigzaggy sprinter) know that the "lateral
component" can be QUITE pronounced, more so in "sprints" that involve
high torque efforts at slower speed, such as going uphill.
> I think that if you viewed the tire tracks from the top, you'd see relatively small angles between the tire tracks and the intended direction.
DR
Dan O
Aug 2, 2012, 3:00:44 PM8/2/12
to
On Thursday, August 2, 2012 8:04:49 AM UTC-7, Gary Kunstmann wrote:
> Been meaning to query this group on subject information. Noticed that
>
> field sprints result in extreme back/forth leaning of bike frames as
>
> riders attempt to increase the power applied to crank. Also noticed
>
> similar techniques in time trials to a lesser degree and even road
>
> riding. Understand the purpose and concept...
> Been meaning to query this group on subject information. Noticed that
>
> field sprints result in extreme back/forth leaning of bike frames as
>
> riders attempt to increase the power applied to crank. Also noticed
>
> similar techniques in time trials to a lesser degree and even road
>
I think maybe you misunderstand the purpose and concept. They're not tipping the bike in an *attempt* to increase power applied to the crank; they're tipping the bike to counterbalance the force they're *successfully* applying to the crank.
http://www.physicsclassroom.com/Class/newtlaws/
> ..., but the technique also
>
> seems to result in the wheel tracks following a zig-zag path rather than
>
> the shorter straight line distance to the finish line.
>
Ride Bike!
> seems to result in the wheel tracks following a zig-zag path rather than
>
> the shorter straight line distance to the finish line.
>
>
>
> Has anyone done the math to prove that the added power applied to the
>
> crank results in a decrease in time to the finish line that is greater
>
> than the loss of time by riding a zig-zag path to the finish line?
>
http://en.wikipedia.org/wiki/Bicycle_and_motorcycle_dynamics
Fortunately, we don't need to calculate whatever it is you were wanting calculated. The results speak for themselves (the beauty of racing :-)
> Would not the result of the extreme leaning be better if the zig-zagging
>
> was minimized, or even eliminated?
thirty-six
Aug 2, 2012, 4:21:07 PM8/2/12
to
being unstable. The rider tends to lock into the oscillation making
matters worse. It is not desirable and not to be confused with
deliberate blocking which mimimicks the behaviour of a sprinter with
unstable wheels in a more pronounced way. Racing rules should
disallow any rider with this exagerated action (wheels tracking wider
than shoulders) even if it does not hinder another as it may lead to a
fall so potentially causing unecessary injury. The style generally
should not be encouraged.
DirtRoadie
Aug 2, 2012, 7:18:00 PM8/2/12
to
of the lateral deviation and minimal other assumptions.
Looking a video head- on it looks like a rider may commonly "sweep
out" a path .3m in width (~1 ft).
This full lateral excursion takes place within a pedal cycle (two
pedals strokes, R-L).
A single pedal stroke accounts for the entire lateral movement in one
direction. That same single pedal stroke accounts for 1/2 of the
distance the bike travels in a pedal cycle - also known as "gear
development."
A 53x12 sprinter's gear is "119.25 inches" which gives a development
of .08 x 119.25 = 9.54 meters, half of which is 4.77.
(shortcut here: http://en.wikipedia.org/wiki/Gear_inches#Calculating_metres_of_development
)
So with these assumptions, we have measurement for the (1)lateral
deviation and over a section of the (2) non- straight path, i.e, two
sides of a right triangle.
Simple trig gives us the angle of deviation from straight is arcsin(.
3/4.77)- about 3°
And the ratio of the longer to straight is 4.77 / Sqr((4.77 ^ 2) -
(0.3 ^ 2))
Or 1.002
Changing only the gear - to 39/15, the same routine
gives 1.006
A small increase over the straight line in either case.
These are quickie calculations that assume straight lines rather than
the somewhat longer sinuous path that the wheel would actually be
following.
DR
Gary Kunstmann
Aug 3, 2012, 6:46:47 PM8/3/12
to
effect by changing technique.
Joe Riel
Aug 3, 2012, 7:47:00 PM8/3/12
to
Gary Kunstmann <gkun...@veawb.coop> writes:
Assuming the path is a sine wave, fractional increase in length is
approximately
dL/L = (pi/2*w/L)^2
where w = total width of path
L = forward length of one full revolution
Using w = 0.3 m
L = 9.54 m
gives
dL/L = 0.0024
which agrees nicely with DR's straight line approximation.
As noted, that represents the increase in the path of the contact patch of the
tire. The path of the rider through the air increases by a smaller value.
--
Joe Riel
approximately
dL/L = (pi/2*w/L)^2
where w = total width of path
L = forward length of one full revolution
Using w = 0.3 m
L = 9.54 m
gives
dL/L = 0.0024
which agrees nicely with DR's straight line approximation.
As noted, that represents the increase in the path of the contact patch of the
tire. The path of the rider through the air increases by a smaller value.
--
Joe Riel
DirtRoadie
Aug 3, 2012, 8:27:20 PM8/3/12
to
On Aug 3, 5:47 pm, Joe Riel <j...@san.rr.com> wrote:
Thanks for fleshing that out. I thought you might.
There is a slight disparity which does not show up in the numbers.
I originally used the "development" as the straight line path (as you
did) until realizing that if we are assuming that the bike's wheels
are zigzagging then the rear wheel is traveling the longer ZZ path. No
matter. Whether solving for the hypotenuse or for the straight leg of
my right triangle the end result (ratio) is the same for the degree of
precision displayed here.
And if one really wants to split hairs, the rear wheel probably does
not deviate laterally as much as the front as we all should know from
tracks we leave after riding through a puddle.
So rather than worrying about the "ZZ factor" I suspect that it would
be more important to develop the general ability to avoid swerving or
veering - to get to the line quicker, to avoid collisions and to
avoid penalties or disqualifications.
DR
> Gary Kunstmann <gkuns...@veawb.coop> writes:
> > DirtRoadie wrote:
>
> >> It's actually very easy to estimate the zigzag path from an estimate
> >> of the lateral deviation and minimal other assumptions.
>
> >> Looking a video head- on it looks like a rider may commonly "sweep
> >> out" a path .3m in width (~1 ft).
> >> This full lateral excursion takes place within a pedal cycle (two
> >> pedals strokes, R-L).
>
> >> A single pedal stroke accounts for the entire lateral movement in one
> >> direction. That same single pedal stroke accounts for 1/2 of the
> >> distance the bike travels in a pedal cycle - also known as "gear
> >> development."
>
> >> A 53x12 sprinter's gear is "119.25 inches" which gives a development
> >> of .08 x 119.25 = 9.54 meters, half of which is 4.77.
> >> (shortcut here:http://en.wikipedia.org/wiki/Gear_inches#Calculating_metres_of_develo...
> > DirtRoadie wrote:
>
> >> It's actually very easy to estimate the zigzag path from an estimate
> >> of the lateral deviation and minimal other assumptions.
>
> >> Looking a video head- on it looks like a rider may commonly "sweep
> >> out" a path .3m in width (~1 ft).
> >> This full lateral excursion takes place within a pedal cycle (two
> >> pedals strokes, R-L).
>
> >> A single pedal stroke accounts for the entire lateral movement in one
> >> direction. That same single pedal stroke accounts for 1/2 of the
> >> distance the bike travels in a pedal cycle - also known as "gear
> >> development."
>
> >> A 53x12 sprinter's gear is "119.25 inches" which gives a development
> >> of .08 x 119.25 = 9.54 meters, half of which is 4.77.
There is a slight disparity which does not show up in the numbers.
I originally used the "development" as the straight line path (as you
did) until realizing that if we are assuming that the bike's wheels
are zigzagging then the rear wheel is traveling the longer ZZ path. No
matter. Whether solving for the hypotenuse or for the straight leg of
my right triangle the end result (ratio) is the same for the degree of
precision displayed here.
And if one really wants to split hairs, the rear wheel probably does
not deviate laterally as much as the front as we all should know from
tracks we leave after riding through a puddle.
So rather than worrying about the "ZZ factor" I suspect that it would
be more important to develop the general ability to avoid swerving or
veering - to get to the line quicker, to avoid collisions and to
avoid penalties or disqualifications.
DR
Joe Riel
Aug 3, 2012, 9:52:24 PM8/3/12
to
(usually that's when I notice the various errors I've introduced).
As you note, that error is small. Essentially it is the same as
approximating 1/(1-x) by 1+x for small x.
> And if one really wants to split hairs, the rear wheel probably does
> not deviate laterally as much as the front as we all should know from
> tracks we leave after riding through a puddle.
Joe Riel
Dan O
Aug 4, 2012, 12:46:57 AM8/4/12
to
> > )
>
> > So with these assumptions, we have measurement for the (1)lateral
> > deviation and over a section of the (2) non- straight path, i.e, two
> > sides of a right triangle.
> > Simple trig gives us the angle of deviation from straight is arcsin(.
> > 3/4.77)- about 3°
> > And the ratio of the longer to straight is 4.77 / Sqr((4.77 ^ 2) -
> > (0.3 ^ 2))
> > Or 1.002
>
> > Changing only the gear - to 39/15, the same routine
> > gives 1.006
> > A small increase over the straight line in either case.
>
> > These are quickie calculations that assume straight lines rather than
> > the somewhat longer sinuous path that the wheel would actually be
> > following.
>
> > DR
>
> Thanks! It seems like it could be nearing 1%. Well worth reducing
> effect by changing technique.
Go for it! (See you on the podium (?)
>
> > So with these assumptions, we have measurement for the (1)lateral
> > deviation and over a section of the (2) non- straight path, i.e, two
> > sides of a right triangle.
> > Simple trig gives us the angle of deviation from straight is arcsin(.
> > 3/4.77)- about 3°
> > And the ratio of the longer to straight is 4.77 / Sqr((4.77 ^ 2) -
> > (0.3 ^ 2))
> > Or 1.002
>
> > Changing only the gear - to 39/15, the same routine
> > gives 1.006
> > A small increase over the straight line in either case.
>
> > These are quickie calculations that assume straight lines rather than
> > the somewhat longer sinuous path that the wheel would actually be
> > following.
>
> > DR
>
> Thanks! It seems like it could be nearing 1%. Well worth reducing
> effect by changing technique.
Dan O
Aug 4, 2012, 12:57:33 AM8/4/12
to
On Aug 3, 6:52 pm, Joe Riel <j...@san.rr.com> wrote:
Okay, I wasn't *sprinting*, but I was tipping the bike side to side
pretty dramatically climbing a long grade yesterday on a narrow road
with essentially no paved shoulder but a white stripe at the road
edge. Not a lot of traffic but they don't want to follow a slow bike
up this long grade on their way home from work, so I ride *right* on
the white line. Tipping side to side to stay upright while applying
power off axis, I weaved a bit but stayed pretty much right on the
line.
But I wasn't staying on the line to maximize efficiency of propulsion;
I was doing it to show overtakign traffic that that was all the road I
needed and it was okay for them to pass carefully. For that matter,
efficiency itself has merit, but is not the holy grail.
Racers may politely listen to armchair analysts, and I suppose smart
ones will even give it due consideration, but when the race is on,
they do what they know in their bones will make the bike go fast.
pretty dramatically climbing a long grade yesterday on a narrow road
with essentially no paved shoulder but a white stripe at the road
edge. Not a lot of traffic but they don't want to follow a slow bike
up this long grade on their way home from work, so I ride *right* on
the white line. Tipping side to side to stay upright while applying
power off axis, I weaved a bit but stayed pretty much right on the
line.
But I wasn't staying on the line to maximize efficiency of propulsion;
I was doing it to show overtakign traffic that that was all the road I
needed and it was okay for them to pass carefully. For that matter,
efficiency itself has merit, but is not the holy grail.
Racers may politely listen to armchair analysts, and I suppose smart
ones will even give it due consideration, but when the race is on,
they do what they know in their bones will make the bike go fast.
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