Thrusting for the line

[ClichéGuevara]

Seen a few clips of races both road and track where riders thrust their handlebars forward at the finish line. I can't remember which race, but the commentator felt that one rider lost because he didn't thrust like his opponent did.

Thing is, and I know I'm a simple soul, but I cant see how it would possibly work. Surely if anything it would slow you down?

 

[festival]

Try it.

 

[Alun]

Ooooh er missus!

 

[ClichéGuevara]

I d

Try it.

I did, but apart from looking a total wally on the high street, it didn't seem to make much difference.

I reckon I must have looked like someone training for a part in the Full Monty.

 

[Flying_Monkey]

You can 'throw the bike' effectively, but it's all about timing and direction. Think about it - if two riders are going at the same speed mainly through the use of their legs, and then one adds a small amount of extra thrust from their arms and upper body, it will add a tiny amount of acceleration. You have to make sure the thrust is in the right direction, and of course, the movement will disrupt both your aerodynamics and your ideal position over the pedals, so you will probably lose speed after the initial acceleration is over. So timing is crucial. It has to be near enough to the line that you get ahead of your opponent, but not so far away that you start to lose the effect in time for your opponent to come back at you.

 

[ClichéGuevara]

You can 'throw the bike' effectively, but it's all about timing and direction. Think about it - if two riders are going at the same speed mainly through the use of their legs, and then one adds a small amount of extra thrust from their arms and upper body, it will add a tiny amount of acceleration. You have to make sure the thrust is in the right direction, and of course, the movement will disrupt both your aerdynamics and your ideal position over the pedals, so you will probably lose speed after the initial acceleration is over. So timing is crucial. It has to be near enough to the line that you get ahead of your opponent, but not so far away that you start to lose the effect in time for your opponent to come back at you.

Cheers. I felt sure they didn't do it for a giggle and your answer does make sense. It just seems counter-intuitive to me. It seems almost like sitting a fan on a yacht and expecting it to fill the sails and move the boat. As you say, a tiny thrust in the right place can make a difference.

 

[Zakalwe]

It's like dipping your head over the line in a 100 metre sprint.

 

[oldroadman]

Cheers. I felt sure they didn't do it for a giggle and your answer does make sense. It just seems counter-intuitive to me. It seems almost like sitting a fan on a yacht and expecting it to fill the sails and move the boat. As you say, a tiny thrust in the right place can make a difference.

It's counter-intuitive to push slightly on the right side of the bars to tighten a left turn, but the physics work.

As for the second highlighted part......what can you say?....

 

[thom]

You can 'throw the bike' effectively, but it's all about timing and direction. Think about it - if two riders are going at the same speed mainly through the use of their legs, and then one adds a small amount of extra thrust from their arms and upper body, it will add a tiny amount of acceleration. You have to make sure the thrust is in the right direction, and of course, the movement will disrupt both your aerdynamics and your ideal position over the pedals, so you will probably lose speed after the initial acceleration is over. So timing is crucial. It has to be near enough to the line that you get ahead of your opponent, but not so far away that you start to lose the effect in time for your opponent to come back at you.

In the detail, I wouldn't say it's exactly like that because you don't cause acceleration or overall momentum change to the combined travelling unit that is your bike and body by thrusting with your arms.

The physics is related to changing your centre of gravity (COG) in relation to the bike. The overall COG of the body and bike will in the absence of acceleration/deceleration (force through the wheels) continue with the same momentum/speed. If you move your body back in relation to the bike, the bike itself moves forward relative to the overall COG, so the front wheel is further forward but the overall momentum is preserved. It will move further forward (relative to COG) the more you can shift your weight back. If you just released your hands gently and slowly move them back behind your head..., it will move further than if you do it in one sharp thrust but still hold the handle bars and don't move your body as much. But as you point out, you'd lose on aerodynamics and on reduced power output so that doesn't do you any good.

My point being, in a vacuum, without pedalling... it doesn't matter how violently you push, just how much you can shift your COG in relation to the bike's COG and after the push, you would have the same speed as before.

Sorry to be pedantic...

 

[Flying_Monkey]

...

I will have to take your word for it!

 

[thom]

I will have to take your word for it!

You're basically right but my point is after the action of adjusting your position, you have the same speed as you had before. You did not gain speed overall.
Nuff said ;-)

 

[Zakalwe]

I suppose a better analogy would be to swing ones shopping bag while walking home, you'll have a burst of speed for a moment in the forward swing, followed by a fight with gravity and momentum on the back swing.

 

[Slaav]

In order to attempt to confuse things.... look at rowing!

If you were to watch and measure the speed of the boat at certain points, you would clearly see that on the stroke, the rower is effectively propelling the larger mass, the rower, up the rails/slider and into the direction of travel. On the slide forward, the boat effectively shoots forward a bit. Timing this properly at the end of the race is an obvious progression as some races are won by cm rather than metres.

In swimming (completely different but also similar ) the stroke is timed in the last 10m or so to ensure optimum contact with the wall. Reaching forwards, effectively slows the simmer down so you wouldnt really want to fall just short and put in another stroke.

Bringing it back to the bike and the excellent explanation above, make it even simpler...

Newtons laws of physics include something like 'equal and opposite force' so if the body is 'pushed' backwards against the bike, the bike is propelled forwards! But timing is key obviously

Anybody confused or is the red wine kicking in again?

 

[Flying_Monkey]

The rowing analogy is good. Cycling does not normally have a rowing type motion pattern. But the thrust at the line is more like a stroke in rowing, which propels you suddenly forward adding to the speed you had already.

 

[Fnaar]

I agree that a good thrust at the end can make you come first.

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