Efficiency of Drafting?

That number seems ok, but I believe it relates to energy used, not time saved.

And the slower the running speed, the less energy is saved as the mass of air being moved becomes less of a factor.

Thanks.

4 seconds per lap seems too high, think about doing a workout with a group, can you run 4 sec faster per lap simply because your running behind someone?

drafter wrote:

4 seconds per lap seems too high, think about doing a workout with a group, can you run 4 sec faster per lap simply because your running behind someone?

ichabod crane wrote:

That number seems ok, but I believe it relates to energy used, not time saved.

There's a graph in Daniels' Running Formula showing the cost of headwinds/tailwinds. This might give you a ballpark estimate but not a precise value as someone ahead of you isn't a perfect wind block. In general though, it is a non-linear relationship (I remember working on this a year or so ago and it was something like the energy requirement went up as the 1.5 power of wind velocity, not quite square law as classical physics wind resistance at normal speeds, of say cars, would predict). In simpler terms, the drag increases faster than the wind velocity so if you double the wind you get more than a doubling of drag. Thus, the faster you're running or the greater the headwind, the more advantage you get from drafting.

I ran a half marathon last Spring and a portion of it had a modest headwind on a flat section. Another guy and I agreed to trade miles leading/drafting. The drafting position was noticeably easier but not a ton, I'd say maybe a few seconds per mile anyway. We were running in the 5:50's and the headwind was probably no more than 5 MPH. I imagine it would've been better if there had been a large pack.

Didn't Daniel's write in his book that 6:00 pace in a 15mph wind is like running 5:00 pace? I dunno bout that.

Alan

I don't know, Alan. When I get home I'll look it up. It sounds familiar though. Gotta admit, one doesn't often run in a steady 15 MPH wind. Gusts maybe but not steady, at least not in my neck of the woods. Around here in March it's more like 5 to 10 on average with spotty bursts of what seem like 30. ;-)

my feeling is that at 5 minute mile pace, sheltering behind someone is worth half a second per lap on a day with a light breeze, obviously more on a windier day.

Runningart2004 wrote:

Didn't Daniel's write in his book that 6:00 pace in a 15mph wind is like running 5:00 pace? I dunno bout that.

Alan

Yep. Page 199 of DRF 2E. The wind graph is on page 126.

Years ago, when Runner's World actually dealt with running, they had a study involving Bill Rodgers. I think the number they came up with regarding drafting was an energy savings of 7%.

JimFiore wrote:

I don't know, Alan. When I get home I'll look it up. It sounds familiar though. Gotta admit, one doesn't often run in a steady 15 MPH wind. Gusts maybe but not steady, at least not in my neck of the woods. Around here in March it's more like 5 to 10 on average with spotty bursts of what seem like 30. ;-)

I, unfortunately, live in North Dakota right now. There have been very many days this year that I have ran when the winds are 15-25mph with gusts of 30+. I know because I'm a loser and usually check the weather channel before I go out. Granted, I don't run directly into the wind the entire time, but it still sucks.

I remember going out for a recovery run once when the winds were about 25 mph. I was trying to run around 135 bpm. When I was running into the wind I was probably jogging about 12:30 pace. I could have basically walked.

Not to hijack the thread, but I really don't understand how to draft effectively. I feel like if I get too close to someone, I start tripping over their feet and vice versa. How close do you run behind someone, and is it directly behind or off to the side a bit. Any other help?

Bump! Wow, I was going to post this under a different alias, but I guess I did that a little too often (didn't think I did it that much)

Even on the calmest of days, we run into a resistance produced by our bodies pushing through the air. At a 9:00 pace you use 2 % of your energy each step, just plowing through billions of invisible molecules of still air. The faster you run, the more energy is required to overcome resistance. A pace of 6:00 in calm air is equivalent to running into a head wind of 10 mph: this means that 5 % of energy is used to overcome that resist­ance. According to Dr. Peter Cavanagh of Penn State, the energy required to run a 6:00 mile against a 15 mph wind is similar to running a 5:00 mile in calm air.

It gets better. According to Dr. Jack Daniels, a runner aiming for a 3-hour marathon, for example, and facing a steady 5 mile-per-hour headwind would lose 11 seconds per mile from a 6:51- per mile effort, and 25 seconds per mile when facing a 10-mile-per hour headwind. That's an extra 5 to 11 minutes over the marathon distance. The slower the runner, the more time:

Twenty-five seconds per mile when facing a 10-mile-per hour headwind. The slower the runner, the more time lost due to head wind. For example, a four-hour marathoner running the entire race in the wind loses approximately 15 to 32 minutes with the same winds.

The good news is that a tail wind helps a slower runner more than faster one. The tail wind produces an energy gain about half as much as is lost with the same head wind.

The three-hour marathoner runs 8 seconds per mile faster, while a four marathoner gets pushed along even more, at between 10 – 24 seconds per mile.

When running into the wind, lean forward slightly to decrease the resistance. Stay relaxed, maintaining good running form and conserving energy. Try to tuck in behind others to reduce the wind resistance. Look for a bigger runner, and keep as close as you can to "draft” properly. Chester Kyle, a professor of mechanics at California State, reports you can cut wind resistance by 31 percent if you can stay 10 feet behind another runner, by 51 percent if you’re within 5 feet. If you're with a pack of runners, take turns shielding each other. Hang with the group as long as you can. The effort will be far easier than if you are battling headwind alone. Again, as was mentioned earlier, the energy required to run a 6:00 mile against a 15 mph wind is similar to running a 5:00 mile effort in calm weather conditions (a minute faster per mile effort). So you need to figure that into a situation when your options are either to slip into a pack of runners at a pace that is slightly faster or slower than your goal pace per mile.

When you have a tail wind, try to take full advantage of it by moving away from the pack--go behind the others, or to the side in order to sail better!

Finally, adjust your pace for the wind. The best strategy is the same as the one used when you are running up and down hills: maintain equal effort. You'll lose time if you have equal amount of head and tail wind in the race. So, don't be disappointed if you run much slower than your goal time because of the strong wind. On the other hand, don't think you’re entering a new dimension if you run a super fast time with a stronger tail wind.

Plan in advance if it's a windy day: know where on the race course the wind will help or hinder your efforts. Look for open stretches (such as fields or bodies of water) that present challenges, as well as those stretches that are sheltered from wind. If you know that a certain turn in the course will bring a sudden change in the wind, you can mentally prepare better.

-Excerpts taken from A Runners Hand Book by Bob Glover

distance guy wrote:

The good news is that a tail wind helps a slower runner more than faster one. The tail wind produces an energy gain about half as much as is lost with the same head wind.

But it's worth repeating that no matter how fast or slow you are, you never get back from a tailwind what you had to put into the headwind.