Friday, April 18, 2008

Racing - How to Get Out of the Wind

One of the great mysteries of cycling is the whole draft thing. When I tell the uninitiated that drafting is important, they look at me like I sprouted a third eye or something. An easy "proof" is to point out that racing cyclists tend to group together. I also point out that although the speeds are different, NASCAR racers group together for the same reason - drafting.

I then point out that about three quarters of a rider's energy goes into overcoming wind resistance. A long time ago someone calculated that on the moon, with 1/6 the gravity and no wind resistance, a cyclist could theoretically go over 2000 mph. I haven't confirmed that but it doesn't seem unreasonable, and the article had all the math in it. Of course there's no mention of what a slightly unbalanced wheel will feel like at 2000 mph but, remember, it was all theoretical.

Cyclists, when riding, are by default moving forward. This causes an immediate headwind relative to the rider. If you are riding 10 mph, you have a 10 mph headwind to overcome.

Since the air is rarely still, the rider needs to factor in the current wind direction and speed. You can do a lot of force vector analysis to calculate exactly how hard the wind will hit you and from what direction, but by the time you have done the calculations, something would have changed - your speed, the wind speed, or direction of travel.

There's a much quicker, easier, and more adaptable way to calculate perceived wind direction. I favor this type of calculation, the intuitive type, versus the "proof and theorems" type.

For me, intuition is easier and better than proofs. I lack some of the expert knowledge to prove things, but I can observe and deduce behavior through intuition.

For example, I had a long discussion with a physics type person at work one day about the benefits of deep profile rims (he noticed my wheels when I brought my bike in). I explained to him that, at 30 mph, the tire on the ground, unless you're skidding, is going 0 mph. The hub is traveling at 30 mph. And finally the top of the tire is going 60 mph.

Since air resistance increases exponentially, the lower part of the wheel (going 0-30 mph) is relatively insignificant. However the upper portion (30-60 mph) is quite important. A deep profile rim removes spokes from the ~55 mph speed wind and drops them into the 40-45 mph speed winds.

This is extremely significant for a vehicle that puts out, say, 200 watts on average, and peaks at 1000-1500 watts (two horsepower since each HP is 746 watts).

But I had no "proof" about my wheel thing. It was all intuitive. Being one that needs proof, the physics type person went home, did all the vector analysis, and announced, the next day, that indeed this was the case.

I could do an "Intuition > Proof" but it's not always true so I can't. I believe, for example, that thunder is caused by clouds kissing - it's easily observed during a thunderstorm. But I have no proof.

Anyway, finding shelter behind another rider is not always easy. Just ride behind the other guy, right?


This only works if you're riding into a direct headwind or no wind at all. But if there's just a touch of crosswind, you really should be to one side or the other. Even at insanely high speeds (200+ mph), NASCAR drivers stagger their line just a bit. Cyclists, with their lower self-induced 20-30 mph headwinds, will usually sit offset to the next rider. But how far?

Ah, now we get into the temple's secrets.

I told the following to the guy who'd eventually be one of my groomsmen, obviously a very good friend of mine. At the time he was 15 or so, all distracted with girls, and couldn't focus on some of the things I told him about bike racing. So I tried to relate everything to girls so that he would both focus and remember.

He, too, had a difficult time figuring out where the wind came from. Since it's relative to your speed (i.e. a 20 mph wind perpendicular to your direction of movement when you're going 20 mph feels like it's coming from a 45 degree angle, not 90), you need to figure out wind relative to you at the speed at which you're riding/racing.

Easiest way to do this is to look forward and turn your head left and right. You'll hear the wind change as the air hits your ears at a different angle.

Now here's the key, this is what I told him. You'll never forget, and in fact I get some of the guys telling me, at random windy races, "I never forgot what you said about how to tell where the wind is coming from".

When you feel a gentle, perpendicular breath into (not across) one ear, just like your girlfriend does when she's playing naughty, then that ear is facing the wind. Therefore you know that's where you want to put something to block the wind, probably another rider.

The confirmation is that there is no girl at the other ear. If both ears are getting something, either you're really lucky or you're not facing one ear to the wind - you're probably looking into the wind, and both ears are getting a piece of it.

Since perceived wind direction (takes into account your riding speed) and actual wind direction differ, you cannot base your shelter needs just by walking around the course and saying "Okay, wind is from the right here, then the left after we turn". However, if you guess at how fast you're going to race and how hard the wind is blowing, you can make a pretty good guess at where to sit relative to the other racers.

Keep in mind that shelter at one point of the course may result in being in the wind on a different part. You'll need to decide where shelter is most important and work backwards from there. So say the worst wind at on course (I'm thinking of Plainville, CT) is a crosswind from the right on the backstretch once the tall reed stuff goes away. You want to be on the left then. But that means that unless you do some fancy wheel work, you'll need to be on the left going into the backstretch, and maybe the wind hits you from the left on the main stretch. So is the wind worse on the main stretch? Do you have time to move over so you have protection in both spots? How comfortable are you at moving from one side of the group (or a rider) to the other without making anyone leery of what you're doing?

Here's the key. If you move around correctly, no one will notice you doing it. I did it all race long at Plainville the last time I was there and no one really realized what I was doing. Maybe one or two did but they don't read my blog or BikeForums.

My race consisted of being more right at the start/finish, turning, moving to the left for that short straight, right as we beared right (and there are those tall reeds to the right), then moving to the left for the back stretch once the lawns start (since the reality is that in a crosswind you draft just one rider, I'm really on the left of one rider, but perhaps 2 from the right side of the field). Then I went to the right before the last turn, then got into the middle for the first part of the main stretch. I moved right to set up for the first turn. On maybe one lap I experimented by going to different spots to see if the wind had changed and it hadn't.

When you're sheltered, it's harder to use the girlfriend method. So you'll need to figure out your shelter pattern before you get sheltered.

Best would be looking around while you do a few warmup laps - no one in the way, easy to get into the wind if you want. Your speeds are artificially low but you can adjust for this as long as you understand the prevalent wind directions. In other words, if your ear tells you to shelter at 8 o'clock (left rear of someone) at 20 mph, at 30 mph it'll be further back (maybe 7 o'clock).

Second best is sitting up and turning your head while you're racing - your head end up above everyone. Well I don't do this too often because I'm too short, but most others can use this method.

Third best is to do it while at the back. You can move from side to side at the back, figure out which side is harder, and avoid it at that part of the course. I do this most frequently, especially since, if I'm at the back, I'm a bit tired. And looking for every bit of shelter possible.

Worst is to get on the wind side of the pack and realize that your side to the outside of the pack is being pummeled with wind. No one wants to let you in so you're stuck out there. Best thing to do is wait for someone to move over on you or to slow down until you find an open spot (i.e. someone not paying attention and leaving a gap).

The latter can be fatal to a race. Unless you have an excellent reason for being in the wind, it's better to sacrifice position to get shelter. I've sacrificed position to gain shelter with 500 meters to go and then gone on to win the race.

Moving up on the outside (i.e. in the wind) is usually a sign of a combination of things:
1. Rider is uncomfortable riding through the middle of a field (#1 reason, in my opinion, and extremely unfortunate since this is a key racing bit of knowledge to have)
2. Rider made an error in scheduling when to move up, and is a bit panicked. Decides prodigal use of energy is worth moving up. Can lead to premature detonation.
3. Rider is so fit that using that much excess energy is really nothing. Kind of like someone who has millions and millions of dollars debating whether to get the $200 shorts or the $205 shorts. Not an issue in that particular race but at some point the racer will end up in faster races and then fall under reason #1 or #2.

Now if in the race this weekend I see a bunch of heads popping up like meerkats and looking around then I know that people have been reading this post.

(Picture stolen from since I couldn't link to it through Blogger)


Colin R said...

If both ears are getting something, either you're really lucky or

I snorted.

Giles said...

That wheel-movement thing kind of blew my mind. It's all relative I guess--movement in relation to the bicycle in general, movement in relation to the ground, in relation to the air, or in relation to the hub. Cool stuff.

It reminded me of the book Bicycling Science, 3rd Edition, which I picked up a few weeks ago. It's sort of geared (no pun intended) for bicycle designers and people with a degree in physics, but it's also an absolutely fascinating read for anyone who is deeply enthusiastic about cycling in general. It covers topics like aerodynamics, rolling resistance, braking, the mechanics of balancing, and a lot more, all with esoteric charts and calculational equations.

I don't think there was anything in it about girls blowing in your ear (I looked), but it's pretty cool anyway.

Anonymous said...

Well going by the picture either 'heads popping up' or maybe 'sniffing occupied saddles'?

Il Bruce said...

Why do you tell people these things? They will only use it against us old timers who figured it out ourselves.

Keep up the good work.

Anonymous said...

Aki - great post! I am working on my pack positioning this year. After getting blown out the back of Johnny Cake Lane Pro1-3 I realized how important shelter is. In the Cat 3 races I can move up in the wind no problem. Not the case in the Pro1-3s. I guess it comes with time and experience.

Aki said...

colin - if you snorted you'll remember, right? :)

giles - I had to wrack my brain to think off a way to explain aero benefits. That's the best I could do.

il bruce - yeah, I know. I dread the day I've shared all I know. I'll be a suffering Cat 4 at that point.

anon - it's easy to skip the basics when you have some fitness. But it always comes back to sting you in the end. Even a young Rebecca Twigg appeared extremely uncomfortable in packs, but she was so strong she could win anyway. Most of us don't have her gifts and therefore need to learn the basics.

Anonymous said...

Rebecca Who? kidding:)

Anonymous said...

really nice blog post. Many thanks!

Here's a good post on the "The Science of Cycling Position" which help as well:

Jake said...

I enjoyed this post. It was quite informative. Now I now what causes thunder!