Descending and Aerodynamics

Doug3

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Jun 24, 2010
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#1
Came across an interesting article about the aerodynamic effect of the rider position while descending.

Basically the result is that having a more radical position on the bike can alter aerodynamics and lead to increased speed, but on the other hand there is a greater risk due to less control over maneuverability. Go figure.

http://pip.sagepub.com/content/226/2/152.full.pdf+html
 

GSAstuto

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Oct 11, 2009
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#2
Very nice! I also like the inclusion of effect of tire pressure. Decrease of pressure from 130psi to 100psi resulted in only .48s difference @ 5km! The other very interesting point taken was that of the importance of mass. Now I know what I'll be working on for the super long descents of HR this year:

1) Getting comfortable in the 'top tube' position - and probably opting for slightly longer frame to accommodate this position better than my current 'undersized' frame.

2) Running seamless tires so I can reduce pressure a bit more and gain compliance for cornering and shock absorption.

3) Packing my jersey at the top of the pass with everything I can and use the extra mass for higher descent speeds, then consume and trash at the bottom. Meaning - I'll move my primary refreshment zone to the bottom of the hill, rather than consume like a madman at the top.

Came across an interesting article about the aerodynamic effect of the rider position while descending.

Basically the result is that having a more radical position on the bike can alter aerodynamics and lead to increased speed, but on the other hand there is a greater risk due to less control over maneuverability. Go figure.

http://pip.sagepub.com/content/226/2/152.full.pdf+html
 
Sep 2, 2009
5
0
0
#3
Yeah, I am always interested in stuff like this.

The practical application of this obviously depends on the environment, but this kind of testing gets the geek juices flowing, certainly.

Perhaps tangential to the topic, but I am interested in discussion of cornering and braking techniques when descending. Working my way through the Gran Turismo 5 training levels improved my cornering no end (honestly).
 

kiwisimon

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Dec 14, 2006
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#4
Very nice!

3) Packing my jersey at the top of the pass with everything I can and use the extra mass for higher descent speeds, then consume and trash at the bottom. Meaning - I'll move my primary refreshment zone to the bottom of the hill, rather than consume like a madman at the top.
Isn't the mass still the same? Is your gut not at the same level as your jersey pockets? Maybe holding the food in your mouth would work better and then simply swallow at the bottom.:heyhey:
 

jdd

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Jul 26, 2008
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#7
Actually, being at an age when a high speed descent crash might put me out of cycling almost forever, I mostly try to use aerodynamics to take it easy and slow myself down.

I would hope that I could handle a crash and not be too badly injured at sub-25kmh.

But at 60+kph...., that's a game-changer.
 

GSAstuto

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Oct 11, 2009
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#8
Mass is the same until it changes. I go up hill very light and each top finish has a refreshment zone at the timing mark. This is where I refill (water, drink, gels, bars). So - yes, if I actually ate everything then it would be exactly the same as carrying in my pockets. But I'll be more conscious to pack more and toss what I don't need on the flats and next hill. Mainly the liquids. So, the more external my load is, the easier it is to modify accordingly. I never really thought about how full my water bottle should be on the descent - so quite a few times I'd only have 1 bottle full and the other empty or partial. An kg down the hill could make quite a difference especially in the shallower descents that require minimal or no braking, yet drag on forever.


Exactly. On the other hand, delaying the pee break until after the descent would make sense.
 

FarEast

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May 25, 2009
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#9
Know the descent like the back of your hand - one of the reasons why the pros will hit speeds of over 100km/h is because they eat breath and sleep on those descents Vockler is a classic example in the last tour - he knew that if he could get to the top first he would be untouchable on the way down as he grew up riding and racing those passes as a junior.

The other important factir is 100% confidence in your own ability, know that if something does go wrong you have both the skill and reflexes to deal with any situation.

Both Tim and Mike Sly have seen me deal with unexpected situations when descending at "Ludicrous Speed"

http://www.youtube.com/watch?v=mk7VWcuVOf0
 

GSAstuto

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#10
Yeah - I think I touched on your 'ability' in another post. I had to smile when I saw you touch brakes, re-connect then do a beautiful 2 wheel drift across the road and never miss a pedal stroke. That is a real bike handler. Most riders freeze up, lockup and crash off the apex under that scenario.

Know the descent like the back of your hand - one of the reasons why the pros will hit speeds of over 100km/h is because they eat breath and sleep on those descents Vockler is a classic example in the last tour - he knew that if he could get to the top first he would be untouchable on the way down as he grew up riding and racing those passes as a junior.

The other important factir is 100% confidence in your own ability, know that if something does go wrong you have both the skill and reflexes to deal with any situation.

Both Tim and Mike Sly have seen me deal with unexpected situations when descending at "Ludicrous Speed"

http://www.youtube.com/watch?v=mk7VWcuVOf0
 

FarEast

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#11
I think another factor is the acceptance of your fate. Like the saying a "A Solider how knows he is already dead is a more efficient weapon" same as a rider that has already accepted he will crash, some of the best crit and DH races have this mentality and it makes them better riders as they have accepted thier fate and can go balls to the wall.
 

GSAstuto

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#12
Release to fate. Yeah - there is a mindset that must prevail. If not, then your operating bandwidth is limited. When that happens - you are indeed limited on both ends. So , when I start thinking too much about risk, I shut it off and just look farther down the mountain. But , I do remember when I was 30 -- and risk was never a factor in the equation. God that was fun!

I think another factor is the acceptance of your fate. Like the saying a "A Solider how knows he is already dead is a more efficient weapon" same as a rider that has already accepted he will crash, some of the best crit and DH races have this mentality and it makes them better riders as they have accepted thier fate and can go balls to the wall.
 

joewein

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#13
Actually, being at an age when a high speed descent crash might put me out of cycling almost forever, I mostly try to use aerodynamics to take it easy and slow myself down.
Same here - sometimes I wish I was dragging a parachute to slow me down more on steep slopes ;)

Descents that are steep enough to counteract significant air friction, relatively short straights in between and either debris on the road, metal grates or sewers that may endanger your tyres - that's a combination I don't much care for.
 

Sikochi

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#15
The other very interesting point taken was that of the importance of mass.
If I remember rightly some of the `pros` back in the days, used to take on lead `water` bottles at the top, to give them a `boost` on the descent.

So thinking about it, you could always pack your jersey pockets with stones once you`ve eaten all your food.;)
 

Sikochi

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#16
I ride very occasionally on the toptube, but more for fun. If anyone is thinking of trying it, then the basic problem is the transition back to the saddle. Easy for the pros who wear skinsuits, but for the rest of us, snagging the clothing can be a problem e.g. jersey pockets, shorts not tucked in properly.

But I don`t do it at anything approaching race speed, like JDD says, I am at an age where falling off doesn`t appeal, and also, unlike the pros, no-one will pay my salary if I am out of action for a long time. Likewise with what Joe says, the pros are riding on roads that have set standards for the surface, and on the average Japanese roads with grates/lips everywhere, you don`t want to be caught out with your weight stuck in the wrong position.

As for the article, why did they use TT positions? I`m not aware of anyone who rides down a 5km hill at 10% like that??? :confused:

PS: For those on carbon bikes, you might also have to take into account the possibility of the toptube cracking with all that weight on it