Sunday, February 22, 2009

Wind Tunnel Visit

On Thursday Chris Pulleyn, Jim Vance and I went to the San Diego Low Speed Wind Tunnel with one of the cyclists I coach to fine tune his time trial position. Chris is the bike fitter from Bicycle Ranch in Scottsdale, Ariz., I have worked with for the last several years. He has set the bikes for nearly every athlete I’ve coached since 2005. At least I think it was 2005 when we started working together. Regardless, it has been many years. Chris is thorough to a fault and always focused on perfection whether the rider is a novice or pro.

Dave Sanford met us at the front door of the tunnel and, as always, gave us a historical tour of the facility. It’s always an impressive sight seeing those big propeller blades. It’s called the “Low Speed” tunnel because the top end for the facility is a 275 miles per hour wind. That’s appropriate for airplanes and Cruise missiles but we would be operating at 25mph.

After the tour we set about getting the bike ready. Chris had already done a two-hour fit on it back in January. We were here now just to make small tweaks to the set up. I’ve found Chris’ fittings to be quite close when it comes to aerodynamics. So I knew we would only make small changes. That’s exactly how it turned out.

The first order of business involved installing an adjustable stem so that we could move the aerobars into several different configurations without changing stems each time. This saved a tremendous amount of time once we got started. And at $850 an hour, time is expensive.

Once the bike was ready and being mounted in the tunnel by Dave’s assistants, Chris, Jim, Dave, the rider and I talked over the procedure we would use. Here is the process we had decided on earlier:

Step 1. Baseline. Conduct a base run using the fit as Chris had originally set it back in January. The first picture here shows that set up. This would serve as the standard by which we would judge all subsequent runs. Each would last one minute once everything was up to speed — wind and rider — but with bike adjustments and getting the tunnel ready each time wound up taking about 10 minutes per run. Chris worked quickly between runs to make the adjustments that follow.

Step 2. Front end height. Once we had a baseline we would begin to tinker with base handlebar and stem height. We would start by lowering the bars 1cm. If that produced a positive result (lower coefficient of drag) we would try 2cm lower. Any other changes in bar height would depend on what we found.

Step 3. Aerobar extension angle. Next we would tinker with the angle of the aerobars and arms in the extended position by increasing the angle 5, 10 and 15 degrees upward on subsequent runs. Later we decided to also try lowering the bars 4 degrees below the base position which was at zero degrees. At this point we also decided to rotate inward the arm extension bars at the grip end.

Step 4. Head position and helmet. Once the front end was optimally set we would experiment with head positions and helmets. Early on, however, we decided that his head position was quite good so didn’t mess around with this. He had brought another aero helmet with him but when he tried it on it was such a poor fit, sitting well up on top of his head, that we decided not to do a run with it. We had early on decided to tape over the vents in the helmet to see what benefits we might get from that based on an earlier recommendation from John Cobb. Since he competes mostly in 20k and 40k time trials this is unlikely to produce a problem. For 40k TTs in the heat he may not tape the vents.

Step 5. Miscellaneous. If we still had time (we had booked two hours) we would try anything that seemed reasonable based on what we had seen in previous runs. As it worked out we tried only one additional change – extending the handlebar reach by 1cm.

Notice that we didn’t intend to make any adjustments to the saddle position. This is what determines power output and we were convinced that Chris had fit this just right back in January when he had used the Retul device to originally set the bike.

The second picture here is the best position we came up with which reduced his coefficient of drag from the baseline run of 0.283 to 0.278 – a 1.8% improvement which translated into a 20-second savings in time in a 40k TT. That’s a small (and expensive!) gain which just goes to show what a great job Chris did in setting his bike initially. This was the second time Chris and I had set a bike and then visited the tunnel with one of the athletes I coach. The last time we shaved off 75 seconds, but most of this was head position and helmet. So Chris is pretty darned accurate at bike fitting when it comes to aerodynamics.

The final changes we adopted for this rider based on the wind tunnel results were:

1. Handlebars lowered 1cm. While at 2cm lower he had better numbers he also became obviously more unstable so this was not a good investment as it would likely reduce power and increase fatigue. His core strength needs to improve and once it does we can probably drop the front end a bit lower.

2. Bar extensions and arms angled 10 degrees up. At both 5 and 15 degrees his drag increased. But interestingly, at 10 degrees he had less drag. Lowering the bar extensions four degrees below the base also increased his drag.

3. Rotated extension grips inward. This lowered his time by about five seconds.

4. Helmet vents taped over. This took off about five more seconds.



At February 22, 2009 9:26 PM , Anonymous Anonymous said...


Would you care to comment on this:;post=2216663;page=1;sb=post_latest_reply;so=ASC;mh=-1;guest=55401150&t=search_engine

I'm not trying to start a battle, but being you're a guy who knows what he is talking about (OBVIOUSLY!), as does Jordan, I'd be very curious to hear either side of this coin.

At February 23, 2009 4:28 PM , Anonymous Anonymous said...

These guys at SLOOOOOOWTWITCH seem to have nothing else to do Joe. But Joe, I wouldn't get into it with them Joe. You can't win Joe and Rappstar is well, just Rappstar.


At February 23, 2009 4:31 PM , Anonymous Anonymous said...

Joe, I would leave the guys on SLOOOOWTwitch alone and not let them rattle you. Joe, they get off on their narrowly pointed self proclaimed triathlon expertise Joe. Life is too short, Joe. Joe, I think Rappstar has become much too impressed with himself Joe.

Good luck and keep writing those great books.


At February 25, 2009 2:44 AM , Blogger Bryan said...

I’ll remember not to visit that site when I’m after constructive information on improving at triathlon.

At February 25, 2009 2:44 AM , Blogger Bryan said...

I’ll remember not to visit that site when I’m after constructive information on improving at triathlon.

At February 25, 2009 8:57 PM , Anonymous Anonymous said...

Holy moley, I just read over 300 posts on Slowtwitch. Who is this Rappstar? Jordan Rapp? A Pro? He should be asshamed of himself and his sponsors should seriously reconsider their support.

A pro should be a professional, they shoudl be supportive, mature and objective. This huys is arrogant and extremely immature.

Jordan Rapp, get a life dude and grow up!

-Bill Rennaker

At February 26, 2009 2:55 PM , Blogger BFW said...

I don't know what they said on slowtwitch or who those folks are. But I can probably guess the general thread.

Full disclosure: I'm basically a younger (poorer) version of the guy in these photos: inflexible and overweight. I value Joe Friel's book and his blog. My (hopeful) PR in a month will be due in large part to what I've learned from reading both.

But let me say this: my first thought upon seeing the picture in this post was, "Tell the guy to lose 30 pounds and see how that affects his aerodynamics."

The rest of the post was lost in that noise.

My constructive feedback regarding this post would be: just write the article, don't show pictures if they don't add to the story.

What do the pictures show?

First and foremost, it sets a tone. Joe talks about expense and time, and wham you see a picture that sets up the rest of the story. What is your impression of the guy's aerodynamics? People are forced to look at his physique and they will notice his extra weight. Like it or not it sets a tone - one that I believe is distracting from the Joe's intended story (using a wind tunnel to improve positioning).

I think that's enough reason to not include the photos.

But there were two photos. Let's look at what we can see by comparing the photos...

1) You cannot tell the bars were lowered.

2) You can tell that the handlebar extensions were tilted upward.

3) You cannot tell the grips were rotated inward.

4) You cannot tell the vents were taped over.

5) Contrary to Joe's analysis, the head positioning is completely different! (yes, I can tell the 2nd picture was taken at rest - not the point). And this point was emphasized by mentioning the other rider saved 75 seconds with head positioning and helmet alone!

By my eyes, the two photos don't lend anything to the story. They only illustrate one of the four conclusions, while countering one of the things that supposedly didn't change.

At the end of the story I was scratching my head... a 1.8% improvement using the best technology available. Everything discussed in this article (the wind tunnel, Chris the bike fitter, Joe Friel himself, the fancy bike, the adjustable stem, travel from Arizona to San Diego) everything screams: professional, top-of-the-line, no holds barred.

Except the man in the picture.

At February 27, 2009 7:30 AM , Blogger Andy Froncioni said...

Kudos to Joe for letting the original post through with the link to SlowTwitch. True class, as usual, Joe, even in difficult times.

At February 27, 2009 2:07 PM , Anonymous Joseph said...

I think there are two main points of this article...

1. The original fit was actually quite good. So good, actually, that professional wind tunnel work could only account for a 1.8% improvement.

2. The client in question was after the best position (in terms of aerodynamics and comfort) possible and he got it. Now we get to benefit from his learning experience by reading this post. The fact that he paid a lot of money is really none of our business and has no relation to his skill level or physique. He had the money and chose to spend it in the wind tunnel. Nothing wrong with that.

I haven't read a single slowtwitch post in over 6 months and think I'm a wiser athlete for it. The conversation over there is borderline insanity and often revolves around one or two people arguing moot points that have no bearing to actual training or the topic involved. It's a case internet anonymity abuse to the T. Maybe not in all cases since some fess up to their identity, but it's not hard to see that some find posting negative things on an internet message board satisfying. If you're wondering what I'm talking about, look for posts that are titled "Critique my position". Lots of fit advice from people who have none to give.

On the other hand, we have this blog, and the many books published by Joe Friel. Informative, scientifically based in many cases, and in all cases...enjoyable to read.

Thanks Joe!

At March 1, 2009 6:25 PM , Blogger Brian said...

I have learned tons from Joe's books and learn something from almost all of his posts on this blog. I appreciate that he shares his advice, knowledge and wisdom for free.

What I learned from this post is that a good bike-fitting session is almost as good as a wind tunnel session. And a lot cheaper.

How we each choose to spend our money is a personal decision. The information Joe presented here helps me decide just how valuable 40 seconds are. That others are unable to benefit from that information reflects on them, not on Joe's choice to share it.


Post a Comment

<< Home