The need for speed



cyclintom

Well-Known Member
Jan 15, 2011
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I did a ride that was supposed to be 47 or so miles a week ago. There turned out to be a wind storm in the pass. At one point the wind was so strong I had to get off and walk the bike in order to retain my balance. One particularly nasty gust actually lifted the bike up and shook it like a flag while I was trying to keep hold of it. Wow. Luckily the top of the pass was only a little over a quarter of a mile further.

I had stayed near the rear for a couple of reasons - I was afraid of wearing myself out in that headwind and also I was afraid that people were going to turn back and the rest wouldn't know where they had gone. In the end no one turned back but four of them were riding slower than I would normally have done in those conditions.

As I reached the top the ride leader announced that we would simply return the way we had just come. I think you all know that my memory is shot from my concussion so all of those lefts and rights etc. were not exactly in the front of my mind.

I started downhill and around each turn I was ready for more gusts like that bad one so I was going pretty slow. Everyone finally passed me before the bottom of the major climb. On the flats we had that howling tailwind so I rather rapidly caught up with the only girl in the group. I hung with her and then her hubby waited for her. I rode behind them for awhile but they were only doing about 24 mph or so. I kicked the pace up to perhaps 28 and went around them and caught up with another. Off in the distance I could see another couple of guys and so I kicked it up to 30 and then to 32 mph where I was spun out. I came up on them pretty fast just as we got onto a very long straight and I couldn't see anyone off in the distance on that one so I slowed back down to 28. When I arrived back we had still done 38 miles but it felt like a double century.

Granted we had a hell of a tailwind but why would I be able to spin out and guys with bigger gears not? I know that the girl was going slowly because the occasional side gust could flip you off the road or worse since it was adjacent to a motorcycle park and there was quite a few pretty stupid drivers carrying their dirt bikes up to ride around in the dust storm. So you only had one pretty narrow lane with no shoulder. But the last group I cought up with didn't seem to have any of those fears. And after we crossed over the freeway the majority of traffic disappeared.

And if someone tells you that aero wheels don't steer you in side gusts - tell them they're full of it. I was literally having to push HARD to keep a straight path.
 
Granted we had a hell of a tailwind but why would I be able to spin out and guys with bigger gears not?
1) tailwind simply provides a ”fixed” offset WRT air drag. Once you go faster than the tailwind you begin to build air drag just like usual. If you’re overgeared enough for your strength and stamina, not even a whopping tailwind will let you spin out.
2) maybe the windy conditions made riding scary enough that they didn’t try particularly hard to go faster.
 
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1) tailwind simply provides a ”fixed” offset WRT air drag. Once you go faster than the tailwind you begin to build air drag just like usual. If you’re overgeared enough for your strength and stamina, not even a whopping tailwind will let you spin out.
2) maybe the windy conditions made riding scary enough that they didn’t try particularly hard to go faster.

I started a posting yesterday that didn't make it on the group since I had to look some things up.

The tailwind was some 25 mph and I finally was spun completely out at 34 but usually 32. This makes the aerodynamic drag for only 7 mph or negligable. So why was I limited in speed at all?

Because the rolling resistance of the tires. Asphalt has a normal coefficient of friction of about 0.004 lbs per lb of load per mph for bicycle tires. So at 34 mph the rolling resistance which was my 185 lbs and the bike's 22.5 lbs (plus weight of clothing) equaled 29 or so lbs of drag. This exceeds the aerodynamic drag under those specific conditions. And with the rolling roads you also have the load of lifting the approximate 212 lbs at 32-34 mph up the specific grade of each roller no matter how small it is.

If you are a time trialist you have to be aware of these things and ready for them. Especially since they are generally doing 45-50 mph under the conditions I was in. This would make a rolling resistance or about 50 lbs of rolling resistane. OUCH!
 

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