Efficiency Drafting vs Aerobars

wiredued

I've heard it takes 30% less power to draft behind some one does using aerobars have the same effect?

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daveryanwyoming

It's not quite as simple as that for either drafting or for aerobars. The savings provided by either depends on your speed, wind direction, size of the group and position in group(in the drafting case), how aero your position is(in the aerobar case), etc. You can play with different CdA values over at: http://www.analyticcycling.com/ForcesPower_Page.html and get an idea of how power requirements to hold a given speed vary with drag. The drafting case is tougher to model but it's also not a fixed number like 30%.

FWIW, I have to put out roughly 300 watts to hold 25 mph on a flat road in the drops on my road bike. I can hold the same speed with approximately 250 watts in my aerobars. So based on that example which has a lot of buried assumptions regarding bike fit, I'm ~ 20% more efficient at that speed in my aerobars.

-Dave

frenchyge

I'd have to guess at numbers, but by feel I'd give a sizeable edge to drafting over riding solo in aerobars. Keep in mind that would also include the discomfort (and lower power) associated with being locked into the bars, in case you're looking at the power side also.

wiredued

Thanks for the input.... I thought the clip on bars might be an equalizer if I get dropped on a club ride but maybe not. I'm going to put them on anyway just for a different position on long rides. I did two 90+ mile rides last summer within 4 days and my hands were killing me on the return ride I had to put my arms on the tops and hang onto the shifter cables for a while.

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kopride

If you are drafting behind the "LORD," air resistance should be zero and the power required would be considerably less than with aerobars.

dhk2

I know a guy who uses them on century rides mainly for comfort as you suggested. Personally, I try the "aerobar position" without aerobars. Just put the forearms on the bars, clasp hands together,flatten the back, tuck in head etc. Not good in a pack of course, or when the road is bumpy, but it seems perfectly safe the rest of the time. My estimate is that getting into this "TT position" is worth .2-.3 mph vs. just being down in the drops. I don't have a PM, so just guessing from looking at bike speed while trying to keep effort constant.

sogood

Problem in this case is that you don't have anything for the hands to pull on.

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Alex Simmons

The drafting impact depends on many factors as Dave has said. Speed especially and how close you ride to the wheel in front.

In my team pursuits earlier this year, my average power when on the front was 459W and when in the line 284W (62% of power when taking a turn on the front).

This was over two runs - 52kph in qualifying and 54kph in the final.

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dhk2

I don't pull on the bars when riding on the flats at normal cadence in TT mode, just try to stay aero and keep a relaxed upper body. Maybe I'm missing out on something, or just using too small a gear

Yojimbo_

459 W and 52 and 54 km/hr.

I sometimes hit 50+ km/hr going downhill.

DirtTurtle

+1 :P hehe

wiredued

Thanks Alex nice power numbers.

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daveryanwyoming

Heck with the power numbers, very nice speeds for a team pursuit Alex. 33+ mph for 2.5 miles from a standing start. Nice job!

Another thought wiredued, the 20% power savings I'm talking about at 25 mph comes from a pretty aggressive aero position. I can ride an hour in that position but doubt I could do much more than that. My hamstrings are typically sore when I finish a long TT in that position and it's a challenge to see up the road riding like that. IOW, it's not the typical cruising aero bar setup you often see on century rides. I'm sure those help on the flats but I'd expect a lot less power savings with one of those comfort setups.

-Dave

Alex Simmons

Our pursuits are 3km.

I was looking for something else when I was reminded of a couple of lines from an item by Asker Jeukendrup (who in turn was quoting numbers himself):

In TP at world cup level (circa 1998-2000), lead riders are doing something in the vicinity of 600W and drafting riders are at 70-75% of that.

but the one that caught my eye was the average power of 98W from a TdF rider with excellent drafting skills in a six hour stage averaging 40km/h.

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