Getting "Slippery"

After deciding upon the goal of attempting to ride sub 2min 30sec for the 2000m Pursuit, I sat down and made a list of every area of potential improvement from physiological (training) and technical (how I manage and pace my ride), to equipment (how "fast" and aero my bike, position and clothing is)

Turned out to be quite a list, and going through the potential time gains (using conservative estimates), it seems there are some places where I might even be able to eke out some "free speed"! Gotta love that idea.

First area I tackled was to try to reduce my CdA (coefficient of drag) by changing my position on the bike. Previously I had just thrown some TT bars on my bike and gone with that.

Knowing that at high speed somewhere between 80% and 90% of the power one produces is "wasted" on pushing through the air, this was an obvious starting point if I was ever going to find some of this "free speed".

I'm very fortunate to have a world class indoor velodrome about an hours drive from my home. The Dunc Gray Velodrome, venue for track cycling at the 2000 Olympics. Perfect for some controlled aerodynamic testing.

If you subscibe to some of the various power training forums around the place, you may have seen some posts from a couple of gentlemen by the names of Robert Chung and Alex Simmons. They have either developed or refined a couple of techniques for using power data to determine the effectiveness of changes to position and equipment.

Now Alex just happens to be a club mate of mine (I transfered to Bicisport last year) and somewhat of a whizz with maths and computers, so I prevailed upon him to help me out with analysis of the data I produced in several test sessions. Gotta say he was very patient, 'cos the first couple of sessions I spent on the track returned some inconclusive data which frustrated both of us a bit I think. But it was all a learning experience.

In all, I spent three separate four-hour test days on the velodrome. It was necessary to have accurate records of atmospheric conditions for each test, i.e. temperature, humidity, barometric pressure, and to note any major changes to these during the testing.

I used my existing track bike (that's another story), standard 32 spoke training wheels with Power Tap hub and (very "slow") high pressure training tyres, standard helmet and skinsuit.

The two test protocols used were a regression method which involved quite a few runs at varying speeds, and the "Chung" method which is basically a continuous ride with speed not necessarily held to a constant.

Alex was interested in testing the two methods back to back to see how they fit, and it seemed to me that the more info we got from either method, the better off I would be.

So that is what we went with. Unfortunately the first two sessions resulted in some iffy data, partly due to the fact that I discovered (after the first session) some loose torx head bolts in the Power tap hub. This is apparently something that can happen when using a Power Tap in fixed gear configuration.

Anyway, after having seen my photos taken during the nationals, I thought my position was to "bunched", too high and too wide. So all I was testing on each of these days at the track, was a single change in bar set-up.

I went 1cm lower, 6cm narrower and extended the aero bars out to within 1cm of the UCI limit (the ends 75cm in front of centre of bottom bracket).
I'll try to get some before and after photos on here at some stage when I can figure out how to do it.

So, what did all this testing show up? Well the position I used at Nationals produced a CdA of 0.0245 and using the regression method, my "new" position yielded CdA of0.235. Using the Chung method, CdA 0.238 .......so .0003 between the two (~1%). That's as good a correlation as I would want.

So I'm now about 3% "more slippery", and just quietly, I reckon there might be a little bit more to be found (e.g. I can go narrower with my elbows with comfort, to more closely follow the contour of my thighs). But all the time spent was definitely worthwhile. Alex predicts that this reduction in CdA is worth ~.4kph of speed and ~1.5sec over 2000m (I was beaten into silver medal position at Nationals by .33sec!)

Incidentally, I did a couple of runs in each position at something approaching cruising speed for my targeted time and the "new" position required 15watts less at 48.9kph (429w compared to 444w).

I'm looking at purchasing a new frame and forks later in the year seeing as what I am using now is a $200 special I got off eBay. I got hold of a second hand rear disc and I used a borrowed front disc at Nationals. I've bought some lycra shoe covers and have a Giro TT helmet. Jeez, these are going to be the most expensive few seconds I have ever "bought".

Next post I will go into a little detail of the training I have been doing in recent times and the races I have pencilled in for the lead-up to the Worlds in October.