Aerodynamics (Page 2)

Triathlons, the crossroads of athletics and number-crunching geekdome (and I say that as an excel-using geek myself - not being mean) . . . gotta love it.  And having only reached my 20-somthing-ith post today, I truly appreciate your distilling a zinger of comparison out of the data that the percentage decrease is about the same across the board on post no. 11 . . . I expect great things from you zo, great things.

actually from everything i have seen, properly used helmets, on MOST riders positions, are the same time gains as wheels.

those with lower head positions tend to get less out of the helmet than those with higher heads (if i remember corectly).

Here is CyclingNews' article on the subject where they did helmet, tri bike and aero bars (less so with wheels, but they also found from before that wheels are about 1- 2 watts more than a helmet):

http://www.cyclingnews.com/tech.php?id=tech/2008/features/jeffs_need_for_speed08

Again, my take:

1) Wheels give you the most.
2) Aero benefits the slower rider more in raw time savings (but is about the same percentage of benefit to everyone).
3) It becomes more critical for the faster riders to be aero because as you go faster your effort to increase your speed goes up a lot faster than your speed - so it is impertive to have a good position to be the most efficient at speed.
4) The benefit of a helmet is all about the riders position - some will not see a benefit from using it.  But it is one of the best benefit per dollar items on the aero list.

Edited by Daremo 2009-04-29 6:10 AM

something else a lot of people seem to miss (sorry rick if this is covered in that article, it wont open on here).

the single largest benifit from a tri bike is not the aero frame but rather the position it allows you to ride in and not the aero frame.

Definitely.  If you have a look at the cycling news article an aero helmet will save you 10 watts whereas simply going from the drops to aerobars will save you three times that.

The one thing I'd  have liked to see in addition to what they did would be the threshhold power (or normalized, or whatever - I'm not a power geek) of the rider in each of the road/drops, road/aerobars, & tri setup. The savings in watts is measuring aero savings as he attempted to keep the speed constant. I'd like to know how much power he would have lost going from this position to this position. I'm sure it's a personal thing, but it seems like he closed that hip angle an awful lot to me and I'd like to know what kind of power that position change would take from him.

For full disclosure, I believe (without any real evidence) that for the ave AGer, you're not going to gain much if any speed going from the drops to a (without forward post) fairly aggressive aerobar position as this article does; what you gain in aeroness, you'll lose in you're power output.

If you have a power meter there are a few methods you can use to fairly accurately test this stuff out for yourself without spending a ton of money in a wind tunnel.

If you join the wattage google group you can get some nicely designed spreadsheets that while geeky aren't too difficult to decipher.  Follow the instructions, enter your data, then make a change, aero helmet, wheels, etc and check out the difference.

As the referenced 'ave AGer', I think I agree with your conclusion about not gaining much speed when all factors are taken into consideration, but with conditions.  I bought my tri bike in December of last year and I have put about 700 miles or so on it since then.  I was slower on the tri bike than my road bike (with no clip ons) for the first 400 miles or so.  I was fitted professionally and found the aero position very comfortable after a few rides, but I still wasn't as fast as when I rode the road bike even though I was upright on the roadie on the hoods.  I came to the realization that (for me) the aero position moved my upper body weight forward so that it was less over my legs and it lessened my power output.  This was especially apparent on hills where I had to mash the pedals.  It wasn't really the closed hip angle as much as the elimination of my body weight to help push the pedals, even when seated this seemed to be a factor for me.  My seat tube angle is really steep to keep my hip angle open, right at 80 degrees.

Now, I have become more accustomed to the position and I have better overall cycling fitness.  I also have better leg coordination in aero.  I have experienced a fairly significant increase in average speeds for the first time over the last few weeks as a result.  Having these factors contributing in addition to the aerodynamics of the bike and wheels, I am hopeful that my ultimate top speed will be higher than if I had stayed with the road bike and clip ons because I don't have a closed up hip angle with the tri bike and I would have with the road bike.  Anyway, I have a $3,700 hole in my check book that says I BETTER be faster...

Greg

Can you quantify this a little better than "noticable faster"? Any specifics (hip angle change/times/weather/HR/power data)? I admit I don't have anything to back up my claims and I may be completely wrong, but I don't have a road bike either

All I could find in your race reports is 2 races 1 week apart with a 1'+ difference in time.

"Can you quantify this a little better than "noticable faster"? Any specifics (hip angle change/times/weather/HR/power data)? I admit I don't have anything to back up my claims and I may be completely wrong, but I don't have a road bike either

All I could find in your race reports is 2 races 1 week apart with a 1'+ difference in time."



going to throw out some numbers of my own.
first, the ave AGer will gain/lose just as much with all the changes as anyone else.

for me, a recent position change where i lowered my bars and brought them back in a bit resulted in a 10 watt decrease and a 5 beat HR increase at threshold. thats a pretty big change in power.

However, even 10 watts lower i was moving faster by far than i was before. the position now is much better fit for me, and after 2 weeks of riding it i am back up to the power levels i was seeing before for threshold at the same HR and able to put out a higher max power now.

I firmly beleive that most people IF they take the time can adapt to a much better position than they are in. without a power meter or wind tunnel its going to be hard to tell what is working though. the issues come in that most people tend to make a huge change, drop their bars 4 in or somthing like that, try it out, it hurts, or they cant put out much power, and they go back. you need to make smaller changes and give it time to sink in and your body to adapt.

newbz, thanks for the data. It's interesting that you've adapted to your new position to equal the power. I also completely agree with everything you said.

My main point is dealing with the large changes, such as what the rider did, when going from a road bike in the drops position to a road bike in the aerobars position. In the article, their was a 30 watt difference between positions required to hold the same speed. I just wanted to point out that with that drastic of a position change most will not gain close 30w of speed increase. Again, here are the pics of the two positions:
Road bike in the drops
Road bike in the aerobars

I suppose I'm just tired of hearing advice to just slap some aerobars on a road bike and get your extra 1-2mph as a result.

Not sure this article supports conclusion #1.  Wheels were not tested.  It was the author's ESTIMATE from prior testing that there was about a 10W savings between HED Trispokes & a more standard wheel (24mm rim,bladed spokes).  And that may or may not take into account differences between testing conditions (e.g. road surface, rolling resistance between tires, etc.).  There are other MUCH better tests out there that document benefit of aero wheels, and differences between aero wheels.

Their data on position & helmet type is a little confusing.  There was a HUGE difference on the speedway in watts @ 40kph with TT2 helm vs road helm on TT bike (33W ), but only a 7.6W difference between helms on road bike with clip-on aerobars.  In the controlled wind-tunnel environment, the helm differences were similar between bikes (6.5 vs 7.6W).  Authors suggested there may have been a powermeter calibration problem on the speedway, but the TT2 helm was a consistent benefit to the experienced TT champion subject.  The relative benefit (or lack thereof) might be quite different for a less-polished (and less flexible) rider's position, but again that was not tested in this article.