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Drafting

Old 01-05-16, 05:12 PM
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callback
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Drafting

Just looking to get some opinions...is drafting effect a LOT more noticeable for lighter rider ?

I'm 15lbs heavier than a friend of mine. On our last ride outdoor, we did a road stretch with a headwind - when I was in front my average power was 370w and his average power was 187w. A difference of almost 200w.

On the same road stretch (same wind direction) after he passed in front of me, his average power was 277w and mine was 294w. The difference is -20w. I was still pushing more watts than him and I was really close to his back wheel. (no more than 6-8 inches). Both were in the drops when not the leader.

We both have the same powermeter, and we did test the accuracy of both power meter against a smart trainer.

15 lbs doesn't seems to be that much for such a difference...any thoughts ?

Sorry for my english.
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Old 01-05-16, 05:41 PM
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What is your height difference? You might be providing a nice big wall for your friend to get behind.
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Old 01-05-16, 05:46 PM
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It's not weight, its mainly height and riding position. I have occasionally ridden with a 6'8" co-worker, its like drafting behind a truck. You can be waaaaay back and still get a good draft. I've also tried drafting a 4'11" woman with an aggressive riding position, it just didn't work at all.
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Old 01-05-16, 05:48 PM
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Originally Posted by callback View Post
Just looking to get some opinions...is drafting effect a LOT more noticeable for lighter rider ?

I'm 15lbs heavier than a friend of mine. On our last ride outdoor, we did a road stretch with a headwind - when I was in front my average power was 370w and his average power was 187w. A difference of almost 200w.

On the same road stretch (same wind direction) after he passed in front of me, his average power was 277w and mine was 294w. The difference is -20w. I was still pushing more watts than him and I was really close to his back wheel. (no more than 6-8 inches). Both were in the drops when not the leader.

We both have the same powermeter, and we did test the accuracy of both power meter against a smart trainer.

15 lbs doesn't seems to be that much for such a difference...any thoughts ?

Sorry for my english.
I would guess that what you're seeing is mostly due to different aerodynamic profiles, perhaps due to differences in build and riding posture.
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Old 01-05-16, 06:15 PM
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I would also guess that it's due to height and posture. Wind direction can also be a large variable.
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Old 01-05-16, 06:22 PM
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callback
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Originally Posted by dougphoto View Post
What is your height difference? You might be providing a nice big wall for your friend to get behind.
Just a little more than 1 inch.

Originally Posted by gsa103 View Post
It's not weight, its mainly height and riding position. I have occasionally ridden with a 6'8" co-worker, its like drafting behind a truck. You can be waaaaay back and still get a good draft. I've also tried drafting a 4'11" woman with an aggressive riding position, it just didn't work at all.
Originally Posted by HTupolev View Post
I would guess that what you're seeing is mostly due to different aerodynamic profiles, perhaps due to differences in build and riding posture.
This was my first guess, but I was in a position with forearms on handlebar when leading, so I was very low. This is still my prefered explanation too but it seems weird to push more watts when behind of someone, even if a have a less aero position.
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Old 01-05-16, 06:28 PM
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We'll need full frontal profile views of both you and your buddy.
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Old 01-05-16, 06:30 PM
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Originally Posted by callback View Post
Just looking to get some opinions...is drafting effect a LOT more noticeable for lighter rider ?

I'm 15lbs heavier than a friend of mine. On our last ride outdoor, we did a road stretch with a headwind - when I was in front my average power was 370w and his average power was 187w. A difference of almost 200w.

On the same road stretch (same wind direction) after he passed in front of me, his average power was 277w and mine was 294w. The difference is -20w. I was still pushing more watts than him and I was really close to his back wheel. (no more than 6-8 inches). Both were in the drops when not the leader.

We both have the same powermeter, and we did test the accuracy of both power meter against a smart trainer.

15 lbs doesn't seems to be that much for such a difference...any thoughts ?

Sorry for my english.
A better number to compare would be w/kg, but a 15lb difference should be a biggie. As others mentioned, your profile on your bike and how aero you and your bike is makes a big difference. Compare how each of you ride, how far down when in the drops, body width, cadence, etc. And of course, don't forget that shaving your legs makes you much more aero......
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Old 01-05-16, 06:39 PM
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Originally Posted by dougphoto View Post
What is your height difference? You might be providing a nice big wall for your friend to get behind.
We call the bigger guys "sheds".
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Old 01-05-16, 06:41 PM
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Originally Posted by Elvo View Post
We'll need full frontal profile views of both you and your buddy.
Watch it, this is a family forum!
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Old 01-05-16, 06:58 PM
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Was his bike red?
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Old 01-05-16, 07:20 PM
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I would try it again, and this time concentrate on your gearing and cadence. Try to run a chimpy gear, and up your cadence. I am a big guy, and when I draft behind my scrawny brother, I have to chimp the gears and match his buzzy cadence to maximize my draft. Basically mimic his gearing and leg speed like you are marching. Works for me sometimes.
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Old 01-05-16, 07:35 PM
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I think we need to call Jackie Stewart.
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Old 01-05-16, 07:47 PM
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Does he have aero spokes?
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Old 01-05-16, 08:09 PM
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Originally Posted by PepeM View Post
Does he have aero spokes?
You'd have to ask his wife. Or his habadasher.
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Old 01-05-16, 09:30 PM
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"Chimp the gears"? That's a new one!
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Old 01-05-16, 09:46 PM
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To the OP,

I have lots of protocol questions, e.g. what does "averaged" mean, exactly, with regards to watts, and does "same stretch of road" mean the exact same length over which you measured? It sounds like you swapped positions and kept riding, so could variations in grade and surfacing explain the variance you see?
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Old 01-06-16, 12:49 PM
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Maybe you were pulling on a slight uphill? Also drafting position is important in a crosswind, maybe your friend is better at riding in your wind shadow.
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Old 01-06-16, 08:49 PM
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Re-reading the first question, it occurred to me immediately that yes, a lighter person should more readily notice the beneficial effects of a draft. It seems that the benefit provided by a draft is in terms of a number of watts saved, so a lighter person would feel proportionately greater relief than a heavy person given the same draft advantage, because lighter people expend fewer watts to obtain any given speed. I don't know what the real numbers are likely to be, but for instance, 20 watts saved out of 200 is better than 20 watts saved out of 250. That's my guess.
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Old 01-06-16, 09:54 PM
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You didn't say he was pulling you at precisely the same speed you were pulling him. And are you certain the headwind was absolutely constant? A 2,3,4mph combined difference can make a considerable difference to power required.

That and you had two flat tires.
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Old 01-06-16, 11:24 PM
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Either your power meters were not accurate or you have a much more upright riding position than your friend. Weight would have negligible impact.
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Old 01-06-16, 11:49 PM
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Was the road level or were you going up a slight grade?
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Old 01-07-16, 12:27 AM
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Sounds like he's getting less of a workout.
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Old 01-07-16, 06:12 AM
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Originally Posted by big chainring View Post
I think we need to call Jackie Stewart.
Its a great day for motor racing (really doesnt read the same without the accent does it?)

as a real light guy, I expect I am not much of a draft but I certainly notice a hell of a benefit behind big guys, coming from the "not much power" camp. When I have been on supported rides before, politely asking a passing tandem for a lift has always been like manna from heaven. Thankyou Lord for this fast rolling large wind blockage.
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Old 01-07-16, 07:51 AM
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Any chance you could swap bikes and try your test again. You might also try side-by-side riding for a bit.

According to your numbers:
You:
Leading: 370 Drafting: 294, difference 76

Friend:
Leading: 277 Drafting: 187, difference 90

So, you both decrease the power significantly when drafting. Just, according to the power meter, you're using about 100w more than your friend.

My guess is one of several things could be happening:
  • Power Meters out of calibration.
  • Friends bike more aero, plus more aero/lower rolling resistance wheels.
  • Are you getting a true "average"? Post analysis?
If you're truly putting out 100W more than your friend, and the problem was in the bike, then swapping bikes, you should blow him out of the water.
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