Friday Oct 28, 2005

Le Tour 2006

So the 2006 route has been announced. It looks interesting. I just wonder how much coverage there will be here in the USA, now that Lance has retired. They already took my Vuelta, please let them let me keep my Giro and Tour...

Tuesday Oct 04, 2005

No bike ride for three days

I've not had a bike ride for three days. I'm having a slight deadline crunch, and I've also had a cold. But I'm getting grumpy, so this can't go on. Tomorrow, come what may I'll be out on my bike before work.


Thursday Sep 29, 2005

Another 500 mile month!

Well, probably. I need to do 22 miles tomorrow morning, but that's typically no problem.

(ETA: yup, done.)


Tuesday Sep 06, 2005

How do I sign up?

I was told today during an IRC chat that "cyclists don't pay taxes", by someone who went on to wonder therefore why cyclists were allowed on the road. I'd like to know how I tell the federal and state governments that I'm a cyclist, so I can stop paying taxes. That'd be cool.


Wednesday Aug 31, 2005

Finally, a 500 mile month

I finally managed a 500 mile month this year. I'd been close, but never quite hit the mark until this month. But now I need to put in four 650 mile months to hit my 10,000 Km target...

Distance per month graph


Friday Aug 19, 2005

Response to training highly individual

I'm reading through the back-issues of Nature on their website, which I got access to with my subscription, and I came across an article about a long-term study of the effect of exercise on fitness. According to the study, different people get different levels of health benefit from the same training. I guess this doesn't come as a huge surprise, but its always a good thing to check whether things that "everybody knows" are actually true. I don't know what the practical conclusion is that I should draw from this. I suppose the thing is to measure what effect a particular regime of training has on me, rather than some population average. If this result were to hold for performance, as well as for health benefit, I suppose it would point towards the value of a personal coach. But I guess that's not really a controversial statement either.


Friday Aug 05, 2005

What next for the Discovery Channel team?

I wonder what Discovery are going to do in the Vuelta. Having already won the Giro and Tour, I guess they have nothing to prove, but it would be a fabulous achievement to take all three the same year.

The other question is, will I be able to see it on TV? It looks like OLN aren't even showing it at the weekends. I guess their cycling season finishes at the end of the Tour de France. I'd actually pay real money to see the Vuelta, I think it's usually a better race than the Giro myself. Maybe one of the online streaming outfits will pick it up. I can but hope.


Tuesday Aug 02, 2005

Flat tire again

Is a flat like a bus? I mean, do you see none for ages, and then three come along all at once? This seems to happen to me a lot, even when I eliminate the obvious common-cause failures. For instance, on Saturday, I went out for a ride, and got a flat, and fixed it by the side of the road. It was caused by a piece of glass in the tire. On Sunday, the tire was flat again, so I opened it up, and there was a tiny hole right near the valve, which I had to use water to locate. Possibly a manufacturing defect, but in any case, nowhere near the previous puncture. Monday, I had an uneventful ride, but this morning, guess what, the other tire was flat.

Statistical theory tells us to expect random events to cluster, and no, I'm not going to crank up Poisson's theoretical apparatus to decide if there truly is an anomoly. It's just one of life's little anoyances.


Thursday Jul 28, 2005

2006 target

I like to have some kind of a target event or events lined up. It helps me with motivation for my daily rides. I think next year, I'm going to aim to get Planet Ultra's King of the Mountains jersey. That involves completing three specific century rides in Southern California, each of which has more than 10,000' of climbing. One of them is the Breathless Agony, which I did this year, so I know it should be within reach. Equally, I was slow on the B.A. and my knee hurt a lot afterwards, so there is plenty of work to do to be more prepared this time.

That's my ideal kind of goal - challenging but definitly doable


Wednesday Jul 27, 2005

Elevated heart rate after vacation

I didn't ride my bike at all during my recent vacation, so I had 8 days of almost no exercise. Now I've been back in the swing of things for several days, and I have an elevated heart rate. It seems to be 8-10 beats higher than normal, all the time. So I wake up with a mid-high fifties instead of a low forties, and when I'm riding at a regular pace, I have 170 instead of 160, and reasonable hills take me up to 185 instead of 175. What is strange is that normally I'd be breathing really hard at 185, but now I'm just starting to notice my breating.

I've never noticed anything like this before after a short break, so I'm keeping an eye on things. I hope everything will return to normal within a week or so. I'm slightly tempted to sprint up a really steep hill and see if my maximum has gone up 10 beats too, but it might not be advisable for medical reasons.


Friday Jul 15, 2005

Gadgets, or not?

I like gadgets. I always ride with a GPS/heart rate monitor, and sometimes with a Power Tap hub as well. I've owned about five different HRMs, two GPSs that I used for cycling, probably tens of conventional bike computers. The thing is though, at my level of fitness/commitment, they don't really help. I improved way more by deciding I was going to do 10 hours a week instead of 7 hours a week than I did with months of sophisticated power measurements and periodized training, and I would have needed nothing more complex than a wrist watch to detect the improvement. But I'm not about to give up any of my toys. They are part of the fun for me, even if it is a bit Fred-ish to have Lance-like measurement systems to show that I'm old, fat and slow.


Thursday Jul 07, 2005

A "utility" bike

Chris's blog entry about his ideal winter bike struck a chord, as I was thinking along somewhat similar lines myself while out riding yesterday. There are things I can't or won't do with Son of Plastic Fantastic. I won't tow my trailer, or take it to the shops. I can't fit fenders (or mud guards, as I used to call them back in the Old Country), or big tires. I won't ride it in actual falling rain (although we don't get that much round here), and I'm loth to ford running water.

I already have a titanium cyclocross frame, which is built up with a Dura Ace triple group. The frame has eyelets that would allow fenders to be fitted, and sufficient clearance for big tires. Unfortunately, the frame has a 135 mm rear spacing (mountain bike standard), but the gits who sold it to me supplied a 130 mm rear wheel (modern road bike standard). I recently bought what will be the third fork to be fitted to this frame, it's a Nashbar (in other words, anonymous Chinese manufacturer's) Cyclocross fork with disk tab. If I were to get a new pair of wheels built, using mountain bike hubs, I could get an Avid mechanical disk brake with the road-specific cable pull, put a disk on the front wheel, and leave the cantilever brakes on the back (since the frame doesn't have a disk tab). Then I'd have wheels which fit with nice big tires, a disk brake for those winter floods, and a bike which would still be light enough to not be a chore to get up hills.

I'd also like to fit lights, because one of these days I'm going to do a double-century, even if it takes me 17 hours. Since riding after dark is not a regular thing for me, I'd stick with a battery-powered system, rather than a generator. Oh, and I'll take a Fizik Aliante for the saddle.

I'd really like to get this going, since there are a number of jeep trails I'd like to explore, and I find them a bit sketchy with my 700x23c tires. One thing we have lots of here is sand, and wider tires roll over loose surfaces better.


Wednesday Jul 06, 2005

What's up with pointy time trial helmets?

Since several people were kind enough to comment favourably on my post about hills and weight, I thought I'd say just a little about aerodynamics, and in particular, time trial helmets.

There are many different ways that drag can be caused. However, for ease of discussion, we can classify by the nature of the mechanism that carries away the energy. Looked at that way, there are the following types of drag:

  1. Pressure drag
  2. Skin Friction drag
  3. Induced drag
  4. Wave drag

Induced drag is drag due to lifting surfaces. The energy goes into forming a wake behind the lifting surface which contains vorticity. Wave drag is roughly speaking the energy carried away by shock waves in a supersonic flow. Neither of these are applicable to cycling, since we don't have wings, and we don't move at near- or supersonic speeds. So we'll say no more about them — refer to any undergraduate aerodynamics text for more details.

Skin Friction drag is the drag due to tangential forces at the surface of the object. It is like the friction you feel when you rub your finger-tip over a table top. The amount of drag varies in a complex way depending on the details of the surface, and the nature of the flow. In general, the frictional drag will be the least for laminar flows and very smooth surfaces. If we hold the nature of the flow and of the surface constant, then the amount of drag depends on the wetted area — the amount of surface exposed to the flow.

Pressure drag (also known as Form drag) is the resultant force obtained when you integrate the pressure field over the surface. That means, for each tiny square of the surface, figure out what the pressure force on it is, and add up the forces, taking into account their direction. You might wonder why the pressure would vary over the surface. Bernoulli's equation (which is really just the conservation of energy cast in continuum mechanics terms) tells us that the static pressure exerted by a fluid against a surface is lower when the fluid is moving faster. (You may have heard this as an explanation of how an airplane flys. In fact, this is just one of the details, not the whole story. But that's a whole other rant.)

Now if you had a fluid with no viscosity at all, you would find that the resultant force would be identically zero. It turns out that the pressure lost as the air accelerates over the front of a body is fully recovered as the flow decelerates again at the back. Sadly, air does have viscosity, although it is low enough that it can be ignored for many purposes. We find that there is a net backwards force on a real object moving through real air, even if we subtract the skin friction out. There is an incomplete recovery of the pressure.

So if we want to minimize form drag, the problem becomes to get the best possible pressure recovery. One thing which inhibits full pressure recovery is flow separation. This is when the flow of fluid no longer conforms to the shape of the object, but instead leaves the surface. There is then an area of "stagnant" flow between the main stream and the object. One of the things that causes this is too rapid of a pressure recovery — and the thing that drives the pressure recovery is the shape of the body. If it is narrowing quickly as we go downstream, the pressure recovery will be rapid, and separation will be more likely. (This is why the classical aerofoil shape has a blunt, curved front part, and a flattish pointy back part.)

So finally, I think we begin to see what drives the shape of the time trial helmet. The point on the back is intended to ease the pressure gradient, to keep the flow attached to the surface, and reduce the pressure drag. But notice, by adding the point on the back, we substantially increase the wetted area, and so the skin friction drag. There are other practical limits to be considered. For instance, no matter how much the aero guys ask them not to, all cyclists put their heads down at some point during the time trial. This leaves the cone on the back of the helmet sticking straight up in the air, which is not ideal. (Incidentally, I speculate that this is why Armstrong's helmet from the pre-saftey-rule days had a two-dimensional trailing edge cut at a raked angle, instead of a simple cone. On the rare occasions that he would put his head down, it seemed to me like the trailing edge of the helmet was almost level, not protruding upwards much at all.) Furthermore, the helmet is shaped with the assumption that the flow comes from in front. But of course, out in the real world, there are cross-winds. Having to cope with flow that isn't perfectly aligned would tend to drive the cone length downwards, because the longer it is, the more of it there is to catch the crosswind. And finally, we have to consider weight, since the cyclist has to hold this up with his or her neck muscles, but with modern materials, that probably isn't much of a concern.


Monday Jul 04, 2005

Something worthy of fear

This morning, as I was out on my bike ride, having just done the climb up Bogert Trail and come down the other side, I was flagged down by a police officer in a cruiser. She said that there was a mountain lion prowling in the area, so I should be very careful. She said to keep scanning all around and look well ahead, and if I saw the animal, not to approach it. Another cyclist also told me that the animal was in the area, and added that — like corgis — they like to chase bikes.

Since several cyclists have been attacked by mountain lions in Southern California in the last few years, I was very concerned. Fortunately, I didn't even catch sight of the moutain lion, and I got home safely. No doubt, even with a puma known to be in the area, I was more likely to be hurt by a car. But somehow that doesn't scare me as much. As I was riding up the main road away from the canyon area and back towards home, I saw a large number of police cruisers and at least one TV crew heading down there, so I guess it is regarded as a fairly serious matter.

Tags: ,

Edited 8/3/2005 to change "killed" to "attacked", to be more consistent with objective reality.

Thursday Jun 30, 2005

Why does weight matter?

Why do (some) cyclists obsess about weight? Why does it matter? Well, if we all rode at a constant speed on level ground, and had perfect bearings in our bikes, it wouldn't. But in the real world, the story is not a very simple one. The human body is not a very capable power plant. I can sustain about 200 watts, and even Lance doesn't do much more than 600 watts except in very short bursts. So the game is to optimize the power budget of the system to make the most of this puny output. Where does the power go? To a first approximation, there are three items:

  1. Rolling resistance
  2. Aerodynamic drag
  3. Gravity (or to be more precise: rate of change of gravitational potential energy)

Rolling resistance is typically small - bearings and tires are very good these days. If we consider riding on the flat, then it is clear that there is no contribution from gravity. So most of our power output goes to overcoming aerodynamic drag. It is somewhat difficult to characterize the drag of a cyclist. Even wind-tunnel modelling is not fully adequate. The reason for this is that in the real world, the apparent wind "seen" by the cyclist is the vector sum of their speed and the prevailing surface wind. This means that the effective wind might not come from head-on. This means that both the effective area and the coefficient of drag are not constants, as they are usually considered to be. Be this as it may, we can still say in general terms that aerodynamic drag goes like the square of the speed relative to the air. From basic physics, power is the rate of doing work, and work is force times distance. So the power is drag times speed, in other words it goes like speed cubed. So if you want to go twice as fast, you need eight times the power output, or put another way, twice the power output will take you about 26% faster.

Now how about hills? The power lost (stored, actually) due to climbing is simply your mass times the local gravitational accelleration, times your vertical speed. If you have a steep hill, and you know the altitude at the bottom and at the top (from a map, or from measuring it), this leads to a simple way to calculate your power output. Provided the hill is steep enough that you are going quite slowly (less than 10 mph (16 kph) but the slower the better), there shouldn't be too much aerodynamic drag to mess up the calculation. Weigh yourself, your bike, and all your gear that you ride with. We need to convert to S.I. units so that the answer will come out in watts. Say it was 150 lbs + 20 lbs + 5 lbs. Divide by 2.2 to get Kg mass - almost exactly 80 Kg. Now multiply by little-g, the earth's gravitational accelleration, to get weight in Newtons. 80x9.8 is about 780 N. Now suppose the climb is 1900' and you do it in 49 minutes. 1900 feet is abuot 580 m, and 49 minutes is 2940 s. So the climb rate is 0.197 m/s. Power is weightxclimb rate, or in this case about 154 watts.

What can we say in general? well for a given hill, power is proportional to speed. It is also proportional to weight. So if you save a couple of pounds, by whatever means, you potentially go around 1% faster. What if we hold the speed constant and vary other parameters? Power goes like the sine of the steepness of the hill. But for the kind of angles we're talking about, sin(x) is approximately equal to x. So if the hill gets a bit steeper, the power output to maintain speed goes up close to proportionally. Power is proportional to weight in the constant speed case, just like in the constant hill case.

So the general conclusion we can draw here, is that riding on the flat (in a time trial, where there's no drafting) is driven by power to drag ratio, whereas riding up hills is driven by power to weight ratio. That's why you don't see the average time trialist get to the top of a mountain first - and why the ultra-elite like Lance and co. are so special





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