Aero bikes and the Pro peloton...

Discuss light weight issues concerning road bikes & parts.
cunn1n9
Posts: 147
Joined: Sat Jan 15, 2011 1:24 am

by cunn1n9

If you do a thought experiment you can see that for all intents and purposes lateral stiffness of the frame simply is irrelevant.

Think about the fact that the component of the force that causes the lateral deflection exists whether the frame is infinitely stiff or a “noodle”. This force is due to the fact that my feet apply force that is offset from the centre line of the bike and so creates a torque around (or about) that centre line that creates the lateral movement/flex in the frame. Now the actual distance the frame flexes is determined by its lateral stiffness. However the force that causes this flex has already occurred and the fact the the frame resists it either more or less happens after the fact of the force being applied. The key thing to understand is that this off centre force component does not contribute anything whatsoever to forward propulsion of the bike. In fact crank based power meters like Stages, Pioneer, Shimano, Infocrank etc. as well as pedal based power meters like Vector, Assioma, Powertap, etc identify this off centre component of the force vector for the express purpose of deleting it from the power calculation. If they didn’t the power reading calculation based on crank flex would be too high. (Some power meters like Infocrank actually orient their strain guages so that this off centre force is eliminated at the actual strain guage. They have a whitepaper with diagrams and explanations of this that if you read you will get a better explanation than what I have tried to provide above).

So it makes no difference whether the bike flexes laterally 0mm or 10mm due to the off centre force component. The force causing this flex doesn’t contribute anything to forward propulsion and is expended before the frame flexes. So the frame being stiffer doesn’t save anything at all. Nor does it flexing back return any useful forward propulsion force either.

There is however a difference in feel though and our minds will perhaps in some peoples experience interpret one as feeling faster than the other but I guarantee that if you pedal exactly the same way in two different lateral stiffness bikes your acceleration would be identical as long as all other variables (weight, aero) were the same.

(However if I was on a vertically compliant frame where the BB actually flexed downwards as I exerted force into the pedals WOULD deduct from the force being applied as the movement is in the same direction as the forward propulsion force. This would be similar to if I used soft soled shoes and as I pushed down I compressed the sole of the shoe. This compression absorbs useful force which is lost as it is in the same direction as the useful force.
However as this vertical flex movement is actually very small it is probably not worth worrying about.)


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by Weenie


TobinHatesYou
Posts: 4027
Joined: Mon Jul 24, 2017 12:02 pm

by TobinHatesYou

cunn1n9 wrote:
Thu Dec 06, 2018 11:57 am

(However if I was on a vertically compliant frame where the BB actually flexed downwards as I exerted force into the pedals WOULD deduct from the force being applied as the movement is in the same direction as the forward propulsion force. This would be similar to if I used soft soled shoes and as I pushed down I compressed the sole of the shoe. This compression absorbs useful force which is lost as it is in the same direction as the useful force.
However as this vertical flex movement is actually very small it is probably not worth worrying about.)

The vertical reflex of the frame returns most of the energy back into propulsion, with a tiny amount of hysteretis loss.

https://youtu.be/BH_AL4rxrp8?t=140

parajba
Posts: 601
Joined: Tue Oct 28, 2008 9:00 pm
Location: London, United Kingdom

by parajba

Lots of interesting points here.

Does anyone know how little or big is the drag of the frame/wheels compared to the rider?

IchDien
Posts: 522
Joined: Mon Nov 05, 2012 12:23 am
Location: Veneto

by IchDien

80-90% rider according to enve.

pkaro
Posts: 22
Joined: Mon Oct 01, 2018 2:40 pm

by pkaro

TobinHatesYou wrote:
Thu Dec 06, 2018 12:13 pm
cunn1n9 wrote:
Thu Dec 06, 2018 11:57 am

(However if I was on a vertically compliant frame where the BB actually flexed downwards as I exerted force into the pedals WOULD deduct from the force being applied as the movement is in the same direction as the forward propulsion force. This would be similar to if I used soft soled shoes and as I pushed down I compressed the sole of the shoe. This compression absorbs useful force which is lost as it is in the same direction as the useful force.
However as this vertical flex movement is actually very small it is probably not worth worrying about.)

The vertical reflex of the frame returns most of the energy back into propulsion, with a tiny amount of hysteretis loss.

https://youtu.be/BH_AL4rxrp8?t=140
Super interesting, thanks for the link. I wish these kinds of stiffness metrics were standardized and published so we could better compare bikes to ones we like.

robeambro
Posts: 602
Joined: Sat Jul 07, 2018 6:21 pm

by robeambro

parajba wrote:
Thu Dec 06, 2018 2:02 pm
Lots of interesting points here.

Does anyone know how little or big is the drag of the frame/wheels compared to the rider?
Frame is very little, less than wheels, and if I recall correctly, even handlebars (shape of the bar + internal cable routing).

Of course, this is not to say that an aero frame is useless, but if one were to dial in an aggressive position (as much as biomechanics would allow), fit deep wheels and have narrow aero handlebars with no cables in sight, adding an aero frame to the equation would definitely not bring huge changes. And probably any aero improvement would be offset by a loss of comfort.

But this is a lot of science, the problem is that some aero bikes are darn sexy. :mrgreen:

parajba
Posts: 601
Joined: Tue Oct 28, 2008 9:00 pm
Location: London, United Kingdom

by parajba

robeambro wrote:
Thu Dec 06, 2018 2:41 pm
parajba wrote:
Thu Dec 06, 2018 2:02 pm
Lots of interesting points here.

Does anyone know how little or big is the drag of the frame/wheels compared to the rider?
Frame is very little, less than wheels, and if I recall correctly, even handlebars (shape of the bar + internal cable routing).

Of course, this is not to say that an aero frame is useless, but if one were to dial in an aggressive position (as much as biomechanics would allow), fit deep wheels and have narrow aero handlebars with no cables in sight, adding an aero frame to the equation would definitely not bring huge changes. And probably any aero improvement would be offset by a loss of comfort.

But this is a lot of science, the problem is that some aero bikes are darn sexy. :mrgreen:
100% Spot on. Trying to decide myself between Venge / SL6. The rational me says SL6, but the new Venge is so so so sexy.

blutto
Posts: 14
Joined: Thu Jun 21, 2012 5:09 pm

by blutto

TobinHatesYou wrote:
Thu Dec 06, 2018 12:13 pm
cunn1n9 wrote:
Thu Dec 06, 2018 11:57 am

(However if I was on a vertically compliant frame where the BB actually flexed downwards as I exerted force into the pedals WOULD deduct from the force being applied as the movement is in the same direction as the forward propulsion force. This would be similar to if I used soft soled shoes and as I pushed down I compressed the sole of the shoe. This compression absorbs useful force which is lost as it is in the same direction as the useful force.
However as this vertical flex movement is actually very small it is probably not worth worrying about.)

The vertical reflex of the frame returns most of the energy back into propulsion, with a tiny amount of hysteretis loss.

https://youtu.be/BH_AL4rxrp8?t=140
....thanks for that video....provides a nice sober look into the problem....that being said there may be one more issue to consider and that is the efficiency of power application by the motor....to wit, does the flex of a frame influence how efficiently power is applied to the pedals in a ,uhhh. physiological sense....in a flexy frame the theoretically perfect circle that we assume a cranket provides becomes, when you factor in the flex between the saddle and the pedal, much less perfect and moves to something akin to a figure 8....so the question could be....is a perfect circle the best option for efficient power delivery or is the rider able to deal adequately with a more "complex circle" ( and is most off line at the critical part of the pedal stroke ) and still produce a goodly amount of power...

....gosh I hope this makes sense cause this was done in some haste...

Cheers

JeffK
Posts: 38
Joined: Sun Aug 03, 2014 5:13 pm

by JeffK

parajba wrote:
Thu Dec 06, 2018 3:04 pm

100% Spot on. Trying to decide myself between Venge / SL6. The rational me says SL6, but the new Venge is so so so sexy.
I had the same dilemma. I went with the Venge. I think the bikes are so similar that it came down to looks and integration (no cables).

robeambro
Posts: 602
Joined: Sat Jul 07, 2018 6:21 pm

by robeambro

parajba wrote:
Thu Dec 06, 2018 3:04 pm
robeambro wrote:
Thu Dec 06, 2018 2:41 pm
parajba wrote:
Thu Dec 06, 2018 2:02 pm
Lots of interesting points here.

Does anyone know how little or big is the drag of the frame/wheels compared to the rider?
Frame is very little, less than wheels, and if I recall correctly, even handlebars (shape of the bar + internal cable routing).

Of course, this is not to say that an aero frame is useless, but if one were to dial in an aggressive position (as much as biomechanics would allow), fit deep wheels and have narrow aero handlebars with no cables in sight, adding an aero frame to the equation would definitely not bring huge changes. And probably any aero improvement would be offset by a loss of comfort.

But this is a lot of science, the problem is that some aero bikes are darn sexy. :mrgreen:
100% Spot on. Trying to decide myself between Venge / SL6. The rational me says SL6, but the new Venge is so so so sexy.
Same! Science (and even geometry for me) says SL6 .. But that Venge, man ...
(and also partly, I think the SL6 doesn't look good in black, and I can't bring myself to like any of the other paintjobs)

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Matt28NJ
Posts: 103
Joined: Tue Jul 14, 2009 3:16 am

by Matt28NJ

parajba wrote:
Thu Dec 06, 2018 2:02 pm
Lots of interesting points here.

Does anyone know how little or big is the drag of the frame/wheels compared to the rider?
Cervelo's take:
...through CFD Cervélo studied the impacts of individual bike elements on the total aero drag of a road bike with its rider. The numbers revealed key elements that had major effects, and these were items where they dove into more deeply to minimize drag:
• 1% – seatpost
• 2% – rear brake
• 3% – front brakw
• 5% – rear wheel
• 9% – drivetrain
• 9% – bottle
• 9% – fork
• 16% – frame
• 16% – front wheel
• 30% – handlebar

robeambro
Posts: 602
Joined: Sat Jul 07, 2018 6:21 pm

by robeambro

Matt28NJ wrote:
Thu Dec 06, 2018 6:37 pm
parajba wrote:
Thu Dec 06, 2018 2:02 pm
Lots of interesting points here.

Does anyone know how little or big is the drag of the frame/wheels compared to the rider?
Cervelo's take:
...through CFD Cervélo studied the impacts of individual bike elements on the total aero drag of a road bike with its rider. The numbers revealed key elements that had major effects, and these were items where they dove into more deeply to minimize drag:
• 1% – seatpost
• 2% – rear brake
• 3% – front brakw
• 5% – rear wheel
• 9% – drivetrain
• 9% – bottle
• 9% – fork
• 16% – frame
• 16% – front wheel
• 30% – handlebar
Thanks!

As I remembered, handlebar matters more than the frame. (Which is definitely something not many pay attention to.. Weirdly, it is very much likely that a "traditional" round-tube bike with aero handlebars and integrated cables would be more aero than an aero frame with a traditional handlebar and cables lying around.

That being said, those %'s may be deceiving, cause they amount to the 100% of the bike-only drag. Which in turn is small compared to the rider's drag.

AJS914
Posts: 3398
Joined: Tue Jan 28, 2014 6:52 pm

by AJS914

This kind of makes me thing that we should all have an aero cockpit and aero wheels. The difference between say a Tarmac with an aero cockpit and a Venge would be pretty small (same wheels, of course).

You'd think that the front wheel would have a greater impact than the handlebar. I imagine they are adding up the whole cockpit - bars, stem, levers. We can only really control the stem by a tiny bit (standard vs aero stem) and the top part of the bar (round or airfoil). Or, use an integrated bar.

On the Trainer Road podcast yesterday, they were interviewing the Specialized engineers. They said 5 watts for an aero road handlebar. An Evade helmet bests that by double, saving around 10 watts.

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wheelsONfire
Posts: 2886
Joined: Mon Jul 07, 2014 8:15 am
Location: NorthEU

by wheelsONfire

Stating "frame", what matters most then?
My guess is headtube / downtube and the flow between HT/DT and fork.
Aero hysteria is a great sales gimmick. Imagine a drivetrain with less friction would be a much better pool to feed money..
Bikes:

Ax Lightness Vial EVO Race (2018.12.21)
viewtopic.php?f=10&t=156137
Paduano Racing Fidia (kind of shelved)
Open *UP* (2016.04.14)


Ex bike; Vial EVO D

by Weenie


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Lelandjt
Posts: 521
Joined: Tue Jan 19, 2016 7:10 am

by Lelandjt

robeambro wrote:
Thu Dec 06, 2018 7:24 pm
Matt28NJ wrote:
Thu Dec 06, 2018 6:37 pm
parajba wrote:
Thu Dec 06, 2018 2:02 pm
Lots of interesting points here.

Does anyone know how little or big is the drag of the frame/wheels compared to the rider?
Cervelo's take:
...through CFD Cervélo studied the impacts of individual bike elements on the total aero drag of a road bike with its rider. The numbers revealed key elements that had major effects, and these were items where they dove into more deeply to minimize drag:
• 1% – seatpost
• 2% – rear brake
• 3% – front brakw
• 5% – rear wheel
• 9% – drivetrain
• 9% – bottle
• 9% – fork
• 16% – frame
• 16% – front wheel
• 30% – handlebar
Thanks!

As I remembered, handlebar matters more than the frame. (Which is definitely something not many pay attention to.. Weirdly, it is very much likely that a "traditional" round-tube bike with aero handlebars and integrated cables would be more aero than an aero frame with a traditional handlebar and cables lying around.

That being said, those %'s may be deceiving, cause they amount to the 100% of the bike-only drag. Which in turn is small compared to the rider's drag.
You're forgetting that every part of the frame can be made more aero. With the handlebar most of it is the same between aero and regular. To reach your conclusion they'd only be considering the flats of the handlebar.

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