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Old 09-24-05, 08:25 PM   #1
TheRCF
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Drafting

Since I have very little experience in group riding, I was wondering, do you still get a big benefit from drafting when there is no wind?
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Old 09-24-05, 08:33 PM   #2
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Yes, because you are still displacing air.
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Old 09-25-05, 03:07 AM   #3
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Going back to Einstein's Theory of Relativity...
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Old 09-25-05, 09:20 AM   #4
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But you do get less benefit the slower you (and your group) are going.
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Old 09-25-05, 11:45 AM   #5
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When you ride, you're creating wind (relative to you). If the air is perfectly still, and you're riding at 15 mph, then you feel as if there's a 15 mph wind. Aerodynamically, the same forces apply if you were perfectly still and there was a 15 mph headwind.

Likewise, if you have a 15mph headwind, and you're also traveling at 15mph, then the aerodynamic effects are the same as if you were traveling 30mph in still air.

Aerodynamic drag is proportional to the square of your velocity, so drafting really only helps at all if you're above 15 mph.
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Old 09-25-05, 09:53 PM   #6
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Well, the drafting definitely helped for the first 60 miles of my Honolulu Century Bike ride today (something like 3400 people were in it!).

But after that, I was worn out. Most other people were too. Those groups who were not, just shot past the rest of us and we had no hope of trying to keep up. Meanwhile, when I came up on other riders, they were dragging even slower than I was so there was not much reason to draft them.

That was one hard ride for me. I think if I do it next year, I'll just start riding when I usually do - 3:00 AM or before - and let the other people eventually catch up to me. That would give me at least 3 hours 15 minutes more time riding before it gets hot - or windier.

I lose a lot of drafting that way, but for the first 10 miles especially, there were so many people, they slowed me down even just cruising.

Bob
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Old 09-25-05, 09:56 PM   #7
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> Aerodynamic drag is proportional to the square of your velocity, so drafting really only helps at all if you're above 15 mph. <

You mean 15 mph of wind effect?

I guess drafting wouldn't have done me any good for the last 40 miles anyway, then. Oh, there were times I was making good time, but mostly I was steadly dropping my speed below 15 mph.

Bob
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Old 09-25-05, 11:21 PM   #8
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How many thousand feet of climbing does that century has?
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Old 09-26-05, 12:37 AM   #9
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Okay, I mapped out the route as best I could on Delorme Topo USA (a couple turns I wasn't positive about, but it shouldn't make any meaningful difference.

Also, this is based on the outbound route - there is at least one (minor) difference in the return route, but it sholudn't matter either.

So, Delorme shows 2329.7 climbing feet and the climbs cover 21.66 miles outbound. Of course, a lot of them would be very minor changes, but I can't work out all those specifics.

Then I reversed things for the return trip and that shows 2326.7 climbing feet over 21.66 miles.

Put them together and you have 4656.4 feet climbing over 43.96 miles.

But putting a human view on it, we have the following climbs that are particularly noteworthy:

Diamond Head, Hawaii Kai Drive hill (call "Heartbreak hill"), the hill up to Makapuu Overlook. Then you have them again in reverse, though I think that on average, the return is a little easier (at least if I wasn't so tired).

There are other much smaller hills that certainly tire me out, but I can't begin to number them or describe them in any detail - I just know I slow down a lot and lose energy.

And I'm still very tired!
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