Is the following statement true (aerodynamics)

Discuss light weight issues concerning road bikes & parts.
wingguy
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by wingguy

Calnago wrote:Like I said, make what you will of the two charts presented.

Like I said, what I make of it is that your conclusion of what we can glean from it does not follow from the evidence provided :wink:

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Calnago
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by Calnago

Good catch on the typo
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GothicCastle
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by GothicCastle

Shrike wrote:On any given route that is a full circuit, i.e. same start and finish point, an aero bike will always be faster than a lightweight bike.


Only if you are riding alone. If you are in a group, it doesn't matter.

RyanH
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by RyanH

This statement can't be true. Take these two examples: a perfectly flat route and a route that features a significant, steep climb and a decent to the start.

That's like suggesting that any given route of exactly 10km at exactly 300w will be completed in the same time. Sure, it may seem like that at first glance until you realize that you spend significantly longer on the uphill than the downhill.
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basilic
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by basilic

Clingon wrote: So even on a 3% gradient twice as much energy (0.77 vs 1.5) is saved by the more aero bicycle;


It doesn't work that way, the percentages of power uphill and downhill do not just add up. Energy or work=power*time. As Ryan says above, you spend a lot more time going uphill.
If you save 1% of time going uphill at speed v (eg 1% of 60 mins), you need to save 4% of time going downhill at speed 4v (eg 4% of 15 mins) to make it even.

Clingon
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by Clingon

basilic, I think my rambling has confused you a little. The calculation is not for a complete circuit but for a 3% uphill grade only. It shows that even to the top of a 3% hill the more aero bike saves twice as much time as a 1kg decrease in weight compared to the baseline given in the RST chart. The point is that a lighter bike will only begin to be faster at gradients substantially steeper than 3%.

Otherwise you and Ryan are of course correct, on a steep uphill-downhill circuit a lighter bicycle will be faster, my point is that the terrain must be quite extreme before this will be the case ie. sustained gradients of greater than 5% with very little flat terrain in such a circuit.

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kgt
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by kgt

I always say that if you want to really see what does matter and what does not just see what the pro riders choose to ride. You will practically see everything: aero, non aero, light, heavy, high profile, low profile, electronic, mechanical, bigger size, smaller size, wider, narrower, higher, lower...

All team managers would agree that riders perform better on whatever they feel is the best for them. That's why you still see 'normal' frames like the Tarmac or the F8 winning the grand tours and not super advanced machines like the Madone or the ViAS.

So forget about 'science' (which in 99% of the cases is marketing BS) and try as many things as possible. Then you will know, by first hand, what suits you better. That will be the best choise.

Clingon
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by Clingon

In a strictly uphill/downhill circuit scenario, which would most favour a lighter bike, I think it is fair to assume for the purposes of this discussion that both bicycles would take the same amount of time to descend. Firstly, descending is not always limited by aerodynamics but also by rider ability, tyre grip etc. Secondly, as others have pointed out, the descent comprises a relatively insignificant amount of the time spent on the course; it takes far longer to go up a hill than down one.

With this in mind, we really only need to work out the gradient required for a light bike to be faster uphill. For Cervelo's climbing superhero mentioned previously, the gradient was 8% before the aero bike was slower. For mere mortals such as myself, 5% is a more realistic estimate, but it all depends on the individual's weight, power output, and the bicycles' respective weights and CdAs.

Basically a circuit must have uphill gradients of at least 5% for a light bike to be faster.

basilic
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by basilic

Clingon, sorry, I misread your statement

Clingon
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by Clingon

kgt wrote:riders perform better on whatever they feel is the best for them. That's why you still see 'normal' frames like the Tarmac or the F8 winning the grand tours and not super advanced machines like the Madone or the ViAS.


This is already complicated enough without touching upon the psychological factors affecting performance, but you are quite right: If a rider thinks their bike is faster then it probably will be. That being said I do like to see firm numbers to guide my choice, marketing BS or otherwise. And the F8 is a surprisingly aero frame :wink:

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kgt
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by kgt

Sure, it is complicated, but psychology is something very, very real. It's not something one can exactly 'measure' though so people tend to think that performance is only limited to things which can be easily measured. Big, big mistake...
Of course if, in your case, self-confidence elevates whenever you think that you ride the most aero or lighter frame then, yes, you should go for it.

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