8/13/14 5:15 AM

While this test isn't exhaustive, it does point out that at least one of the crazy positions used by the pros really does make a serious difference.

http://www.roadbikereview.com/reviews/video-whats-the-fastest-downhill-tuck-position

8/13/14 7:04 AM

I just wish all the *&^%$ wiseguys on the local group rides would descend in a normal position. Makes me nervous as hell when the guy in front/beside/behind me decides he needs to put one arm behind his back or lay on the bars. They want to do that crap solo, fine, but not around a group.

Rant off

8/13/14 10:06 AM

That's an interesting video. Thanks. One thing of note was the top speed was about 42mph for a 6% grade.

Some questions....


At that speed is one really "spun out" as they note. I'm too lazy to use a gear calc, but I would imagine depending on your gearing it can be pretty close to it, if not quite spun out.

You mentioned during a TdF stage that the fastest of the 3 really did not seem to make a difference. I agree. Notably at the speeds which they were descending it surely was much greater than 42miles/68k per hour. That is, at what speed does terminal velocity set in?

8/13/14 10:12 AM

@ 210 lb, I don't try to go faster downhill honestly. I don't have to, or rather I have become too chicken and/or lack the motivation to go 40+ MPH anymore.

I used to love that shit too! ;)

8/13/14 11:42 AM

I use those long but modest downhills to hit mid-high-40's using only a 52-13t, can just hit 50 with a 12 in back.
Pedaling is absolutely required to get to even 40mph on these same grades.
So not spun out in the sense that pedaling is futile.

8/13/14 12:35 PM

quote:

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At that speed is one really "spun out" as they note. I'm too lazy to use a gear calc, but I would imagine depending on your gearing it can be pretty close to it, if not quite spun out.

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8/13/14 12:43 PM

Agreed on not spun out. Close, but not spun out. (My message was not very clear.) At the time I wrote it, I was thinking of sprinters who hit speeds of 40+ mph and are obviously not spun out.

The video still has merit. The 40mph descents is more common/more relevant to those watching it - myself included. No criticism here. Good stuff.

The $64K question is if you are descending faster than 50mph, is there any benefit to one of those positions over the other? Perhaps there is if you are out in front - maybe, just maybe, but it does not appear to be so with a casual look. Somewhat behind another descending rider, with even a minimal amount of draft protection, like in the TdF alpine stages, probably not would be my guess.

8/13/14 12:48 PM

"if you are out in front"

Of what/whom is the question maybe...

8/13/14 1:01 PM

""if you are out in front"

Of what/whom is the question maybe..."

I'm not into looking back to see when going this fast, but riding a rock-solid old Schwinn at least makes that possible.

Yes, I'm a spinner, preferring cranks @165-170mm.

I "shift gears" mentally when I'm spun out, sort of reads "another 5%" and suddenly accelerating smoothly/freely again to the next increment. I liken this to a change in "ignition timing". At some point though, the legs muscles cease to twitch off fast enough, seem to stay tight through the whole 360 degrees if that makes sense.

8/13/14 1:08 PM

"if you are out in front" - meaning no one is in front of you, directly or at an angle, to provide any wind resistance reduction.

8/13/14 1:09 PM

I do the 2nd tuck position with hands near the stem. However, the rider in the video isn't low/tucked enough.

My chin is _almost_ resting on the stem, and butt in front of the saddle (tip of saddle touching my backside).

Would like to see the aero data for the above position.

8/13/14 2:24 PM

I forgot the sarcastic emoticon. ;)

8/13/14 7:07 PM

Don't need a frickin' wind tunnel to do the test. Also they should've checked the ass-off-the-back-of-the-saddle and arms straight one that've often seen Nate Morgenstern do...

I'm sure we've all tried it before. Just use a fairly straight hill, climb it (for training), and roll down (for recovery) in various positions, and watch the bike computer.

Sandiway

8/13/14 7:15 PM

Bicycle Quarterly did some wind tunnel work on descending positions and found that the "hands on the bars at the stem, chin on the stem" position reduced CdA by 1/3 compared to riding in the drops, elbows slightly bent. The position that they showed with hands on the stem could have been significantly lower, so they didn't really get a full comparison with the "top tube" position.

I wonder what could be going on that some riders didn't go faster with the "top tube" position. I use the hands on the stem position when descending but would not consider the "top tube" position because of control issues (and probably discomfort issues too).

8/13/14 7:18 PM

quote:

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would not consider the "top tube" position because of control issues

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8/13/14 9:20 PM

I tried that top tube position a few weeks ago on a hill about like the one they describe. I won't do it again. The position is unstable on my bike and dangerous. Scary to say the least. If you have a quick handling Crit bike, don't do it.

8/20/14 12:32 AM

quote:

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My chin is _almost_ resting on the stem, and butt in front of the saddle (tip of saddle touching my backside).

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