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03/12/2011

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Ed (the real one)

It strikes me that a major safety (and aerodynamic) improvement would be a mirror at 45 degrees that would let you look forward while your face was pointing downwards. A sort of "front-view mirror". It could be attached either to head or bike.

Mike Hardy

I think it's possible to add a couple more tricks to this as well by stacking hands. This both narrows the very front of the rider to more of a wedge, width-wise, as well as - if they lower their helmet using the technique you describe to nearly meet their hands - vertically. Here's an example from Ben Jacques-Maynes during a blazing TT, and I've seen Zabriskie do it as well: http://hcphoto.smugmug.com/DBC-and-NorCal/MercoCUCyclingClassic/Merco-2011-P2/16083080_wWDqc/1/1207712862_AZz6k/Medium

I haven't seen anyone using the skinsuit with "wings" ("extra" accidental I'm sure fabric between upper arm and ribcage creating armpit fairings) that Zabriskie used at the end of last year though

Jgdicker

Joe, John Cobb said that the tail sticking up is a problem. He designed the Rudy Wingspan helmet with the "chopped" back to deal with this issue. The back is similar to the aerodynamic rear end of the Toyota Prius.

Joe Friel

Jim--John is the one who first told me it wasn't a problem. I asked him that in a talk he did a couple of years ago. And re-asked it to make sure I got it right. We later confirmed that he was right in the wind tunnel. Less drag with head down and tail of helmet up. So I don't know what's going on. Need to ask John, I guess.

leighton

hi joe a couple things strike me about this tt i too enjoyed watching.

i think martin's general mass and cda is greater than klodens, as they're seat to tri extension ratio, look very similar i.e. level with the headset.
i think he over comes this(>mass)with power.........i'd love to know what they both put down and watts per kg.
with all the pro wind tunnel reseacrh, the slighter rider should be more aero dynamically sound?

Brian

Hi Joe - I love your blog and your books, they've been helping me take my training to the next level for years. This aerodynamics post coincides perfectly with a "problem" I am trying to figure out, namely I seem to be able to put out some fairly decent power numbers, but can't seem to get my speed results to match up to them. Here is the scenario: I live in Coeur d Alene, can avg 290 watts for at least one loop of the Ironman course (I weigh in at ~77kg), have had my bike fit, but seem to be infinitely mired right at 5 hour pace. The hills seem to be where I lose most of my speed (my avg on the flats is around 23.5-24), and I even increase my watts in the hilliest sections to around 310-330 to try to compensate. I know more info is probably needed, but where would you start troubleshooting my plateau (best IM Cda bike split is 4:55, worst is 5:00, avg watts for the 5:00 on a closed course were only 245). Is it a combo of my aerodynamics and weight, or do I just need to lose some weight, or up my power in the hills even more? I'm ambitious and desperately want to be closer to 4:50...

Joe Friel

Brian--I wish I could tell you. There are many, many variables here. You mentioned one of the biggies--body weight relative to weight. Not always a limiter, tho. I once coached a 90kg IM athlete (very tall) who did 4:55ish in Kona. We focused on him being as fit as possible for the bike and then held back a lot on the ride. I think he could have done 4:45 there but then he would have walked a lot.

Nathan

Joe, I've accompanied John on his trips to the tunnel the last 2 years, so perhaps I can shed some light onto the head down, tail up question. There is a trade off to this, as in, a head down position will get your head in line with your shoulders/back and thus reduce your drag greatly. And despite the tail sticking up, the trade off is still a benefit because of the reduced frontal area. If you want to discuss this further feel free to contact me.

Jgdicker

Very interesting. About 16 months ago, he fitted me. I wore my old long tail helmet for the fitting. He said that my head position with the tail sticking up was a problem, and suggested that I buy the Wingspan. Since that time, I have read other articles that suggest that the "Prius" rear end is very aero. If I am not mistaken, this applies to the shape of tubes as well.

Nathan

If you're a head down guy, then of course a shorter tail would be better than a longer tail. Ideally, you'd "turtle", but as Joe pointed out, that can be hard to do for long distances. The Kamm shape is aero when it applies to tubes, but is used because of the 3:1 UCI rule, not because it's the most aero shape. (See Trek Speed Concept)

Jameson-king

I thought I'd throw in an example. I am with PowerTri and was at the wind tunnel when Joe attended with us a few months ago. A good example is that the Spiuk Kronos aerohelmet, with its long tail, is not so efficient when the rider has his head down. If you can get more of the frontal surface area below the shoulders (like having your head down), then it is usually an advantage. The compromise of putting your head down it having the tail sticking up, but this is still less frontal area above the shoulders, than if your head were up.

Rob Morris

Is it not fair to say though (i do agree with comments by the way) that with Martins position on the bike slightly more upright, he is utilising a much more powerful gluteal activation? The Austrailian pursuiters have proven on the track that actually, that low profile position is not always the best solution if it sacrifices power output? Just a thought

Jeff Harmon

Hi,Joe.
Great article.
Can you speak to the issue of elbow width and aerodynamics?
I have my elbow as close together as is comfortable, which I thought was better for short distances, but I notice that many of the pursuit racers use a wider bar position.
Thanks.

Joe Friel

Jeff Harmon - In theory a narrowed elbow position will improve aerodynamics. In practice it doesn't always work as it _may_ reduce chest capacity thus restricting breathing and for very long events (IM for ex0 it can be very uncomfortable causing the person to frequently come out of the aero position thus compromising aerodynamics.

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