Tom A. wrote:
davidalone wrote:
I'll chime in on the aero versus weight debate:
I am currently studying engiineering, so I amfortunate enough to understand in greater detail cervelos 'col de la tipping point' presentation
I think that presentation has some fallacies. why? because a big part of drag depends on the speed of the fluid- i.e. in our case how fast you are moving relative to the air. Drag consists of both friction drag (dependent on surface area that the fluid encounters) and pressure drag ( dependent on fluid properties, tube shaping and other factors) are affected by the velocity of the fluid. friction drag is the one presented in the col de la tipping point scenario. pressure drag is not because a through explanation and calculation would make everyone drool and fall asleep before it was even fully explained. so that figure of 1.5% savings is very simplistic and not the entire picture.
Ummm...no. I think you might want to study your engineering a bit more. The "Col" write-up uses the total drag (i.e. pressure AND friction drag), which is expressed as the CdA value. Calculating drag force from the CdA and air velocity is fairly trivial.
hmm. yo're right. I confess it's been awhile since I looked at the presentation and I skimmed over it. my apologies.
however I mantain that the drag calculation is NOT trivial. finding the CdA for individual tubes might be simple, but the CdA of the entire frame with different tubes put together, plus the interaction of the riders pedaling legs, is probably not.
styrrell wrote:
Your analysis has a few flaws. One is that it assumes you are riding a TT (no drafting) Where as this thread is about 2 bikes that will be used mostly in situations where drafting is allowed and is a big part of winning strategies.
The second is that weight vs aero is an either or situation. Take the Lightweight (brand) disc wheel. Find a more aero wheel than it, yet its very light. Same with say an 808 (previous version) vs an 808 FC. the 808 is lighter and more aero at certain yaws than the 808FC.
Finally even on a climb its rare to not have small changes in speed. Because these changes are tough to quantify and any one of them results in a very small acceleration they are ignored, but that doesn't mean they dont exist.
You'll find very very few people who will argue that sacrificing a big aero gain for small or even big weight gain makes much sense. You do find quite a people who will argue that any aero gain is more advantagous than any amount of weight loss, and even worse that increasing weight can help performance. Thats what most of these debates center on.
Lets revise- our debate is whether aero OR light is better for road riders. the question is, what KIND of road rider? we can all agree that for a breakaway specialist, ala jeremy roy (FDJ) chavanel, etc.) there is little sense arguing that he'd be better off on an aero bike(unless he's not breaking away for 2/3 of the stage) but I would like to refine your debate further- we want to know if aero or light would be better for going up those hills- so lets put this from a climber/GC rider perspective. these guys will usually sit in the peloton for 70-80% of the race and only go on the climbs, so the aero penalty would more or less be nuetralised. theres no point arguing that aero bikes would be better on the flats, riding alone, in a TT. thats obvious. But I think the question would be why arent the climbers riding aero bikes if , according to cervelo's presntation, they can have an aero advantage should they need it ( say cadel evans at galibier this year, or schleck at the same stage) with no penalty for their climbing?
. with the current technology available, there is a weight penalty of about 200-400 grams between the lightest commercial and most aero commercial bikes. I proposed this test because it gives us an objective measurement- speed going uphill at a certain gradient- that can settle it. this test would give you the pros/cons (in speed) you would gain from running either setup- isn't that the thing being discussed?
I contend that you should not take drafting into account when measuring which bike is better. EVEN when we are referring to a tour climb situation where drafting tactics play a big part. heres why:
1) drafting brings too many variables into play, making your test unpredictable and uncontrollable. will the aero advantage of an aero bike be the same sitting in the dirty air of a drafting bike? probably not. whats the drafting distance you want to measure at. 1m? 0.5m? can this distance be controlled? you have to make certain assumptions in engineering testing- some things are sometiems too complicated to test and you need to make certain simplifications for an accurate result.
2) even if drafting is a large factor in tactics, I predict that the watts savings from both an aero and non-aero bike sitting in a draft will be almost identical- the differences will be so minute that it is immaterial.
3) our test is uphill, and drafting effect goign uphill is much less significant.
so heres the situation. we can more or less assume that our two riders X(non aero) and Y (aero) ride the same tour stage. they are both GC contenders, so they both sit in the peloton, not doing any work at all. they arrive at the foot of our said climb with next to near identical energy levels. (remember they are identical twins in position, weight, etc.)
now we can't have them go head to head, because in a competitive scenario one would draft off the other, and although uphill drafting has little effect, it will give one party or the other an advantage at different times. this is something you would find difficult to controlin testing and in real life. drafting and getting other people to do the work is also largely a psychological art and comes down alot to the physical engine ( can you stay with the person in the first place) and also tactics, peloton alliances, etc. so how do we test objectively? we remove it. get both to do a time trial. uphill. the changes in speed uphill would be normalised because you'd be taking average speed- the drag you'd expereince would be average drag.
once you nuetralise this variable it should become pretty clear which bike is better in a climbing scenario- the one that is the main point of contention in cervelo's presentation. of course, drafting will play a big part in who wins, but the bikes don't decide when or how to draft, the riders do. would both riders X and Y be faster if they had someone to draft, even if it was uphill? undoubtedly. would the speed increase from drafting have an appreciable difference in result? unlikely.
