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BIG difference in descending speed for the same weight?

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BIG difference in descending speed for the same weight?

Old 05-18-15, 10:25 PM
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greenlight149
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BIG difference in descending speed for the same weight?

i was looking at the leader boards for a local climb + descend, comparing my power data to his, up the same 5% climb, we are using the same watts at the same speed, so i assume we are roughly the same weight, however, on the way down, i top out at 58kph while he keeps going and reaches 76kph....wtf. Im wearing pretty form fitting jersey, on an aero bike, 35mm up front and box section in the back (tied to the PT).

now i know at this speed the most important factor is aerodynamics, and of course i was in the drops, trying to get low and minimize frontal area. where is this extra 20kph coming from? only thing i can think of is that hes in aero bars, but thats rather dangerous with the twists and turns.

-5.1% gradient, im 60kg, and just in case you were wondering, i wasnt braking.
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Old 05-18-15, 10:37 PM
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Tailwind? I am too lazy to do speed conversions, but I have gone 40mph with a headwind and 50-55 mph with a tailwind on the same stretch of road.
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Old 05-18-15, 10:37 PM
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Look at his power and cadence on the descent. Maybe he's pedalling where you're not.
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Old 05-18-15, 10:41 PM
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Originally Posted by Elvo View Post
Look at his power and cadence on the descent. Maybe he's pedalling where you're not.
nope hes not pedalling, and during the times when i did pedal with a 400 watt boost for 5 seconds i cant even get nearly as fast.
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Old 05-18-15, 10:46 PM
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Originally Posted by Bunyanderman View Post
Tailwind? I am too lazy to do speed conversions, but I have gone 40mph with a headwind and 50-55 mph with a tailwind on the same stretch of road.
well that would explain it, except on a descend in the opposite direction, he was still 8kph faster

i think the most likely answer is that hes power meter was not calibrated properly.

Last edited by greenlight149; 05-18-15 at 11:02 PM.
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Old 05-18-15, 11:02 PM
  #6  
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Chain ring gear: Is he 54/39 and you are at 50/34? I've out climbed guys only to have them hurtle past me going downhill and think they must have more gear plus more bravery than I do.
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Old 05-18-15, 11:04 PM
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Originally Posted by raceboy View Post
Chain ring gear: Is he 54/39 and you are at 50/34? I've out climbed guys only to have them hurtle past me going downhill and think they must have more gear plus more bravery than I do.
he wasnt pedalling on the way down though, and we were doing the same watts on the way up.
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Old 05-18-15, 11:51 PM
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Was he in an aero tuck? You said you were in the drops. If he was in a full aero tuck, that would explain the not pedaling.
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Old 05-19-15, 01:57 AM
  #9  
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Originally Posted by greenlight149 View Post
i was looking at the leader boards for a local climb + descend, comparing my power data to his, up the same 5% climb, we are using the same watts at the same speed, so i assume we are roughly the same weight, however, on the way down, i top out at 58kph while he keeps going and reaches 76kph....wtf. Im wearing pretty form fitting jersey, on an aero bike, 35mm up front and box section in the back (tied to the PT).

now i know at this speed the most important factor is aerodynamics, and of course i was in the drops, trying to get low and minimize frontal area. where is this extra 20kph coming from? only thing i can think of is that hes in aero bars, but thats rather dangerous with the twists and turns.

-5.1% gradient, im 60kg, and just in case you were wondering, i wasnt braking.
A lot of factors.

Strava power - you sure it's the other rider's real power? Not just estimated?

Aero wheels - a week apart, in similar conditions (wind protected descent) I did the same hill on the same group ride. I was faster doing a sprint-then-coast with 60/90mm wheels than 24mm tall wheels even though I was sprinting and drafting (as I passed) with the non-aero wheels. I see a consistent 3-4 mph difference between the wheels when I coast down the hill to my house (27 mph vs 31 mph). I start the coast at about 11-12 mph as I turn in at the top of a hard-for-me hill. Same tires, pressure, and it's me on the same bike.

How tall are you? How tall is the other rider? If you're taller then you'll be slower for a given weight. Leg length is somewhat important here. For example I'm about 73 kg (160 lbs), 170 cm (5'7"), and my saddle-bb distance is 67 cm. It's very short because I have short legs. Therefore I present a smaller profile to the wind than someone the same height but with longer legs, and I present a much smaller profile than a tall skinny guy. Someone I race against is a foot / 30 cm taller than me and weighs within a couple pounds of me.

Is the other rider solo? Were they on a group ride? My Strava power is phenomenal in a group ride/race where I'm drafting. My real power is almost always similar in range, like 150-190w avg. Strava will underestimate my power in a group ride/race by 200-300w.

Drops is not the fastest - you can pick up some speed (not 20 kph, but maybe 5-10 kph initially) by using an aero tuck. Hands near stem, head way over front wheel (if you're shorter on the bike like me) or resting thigh on top tube and keeping your torso just above the top tube (if you're taller).

If you go over the top of the hill faster you will hit much higher speeds. If the other rider sprints they'll hit much higher speeds, even if he's coasting a lot after the sprint. If you hit the steepest parts faster you'll have more time accelerating at the higher speeds (it's quick to accelerate from 20 to 30 kph, less so from 70 to 75 kph), and if you're already at top speed, you'll maintain it longer.

On a downhill, when I'm trying to put power to the pedals, I'm spiking my power to 800-1000w. I don't do that intentionally, I'm just trying to accelerate here and there while at speed, then returning back to a tuck. The power spikes really help push the speed up. 400w is not going to contribute a lot on a shallow descent.

Cornering, if there are corners. If you're not cornering well then you'll lose tons of speed. Maintaining momentum can really help push speeds up on a descent.
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Old 05-19-15, 05:23 AM
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Riding in a group is my guess. Maybe he got a truck to drive in front of him.
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Old 05-19-15, 07:54 AM
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Originally Posted by carpediemracing View Post
A lot of factors.

Strava power - you sure it's the other rider's real power? Not just estimated?

Aero wheels - a week apart, in similar conditions (wind protected descent) I did the same hill on the same group ride. I was faster doing a sprint-then-coast with 60/90mm wheels than 24mm tall wheels even though I was sprinting and drafting (as I passed) with the non-aero wheels. I see a consistent 3-4 mph difference between the wheels when I coast down the hill to my house (27 mph vs 31 mph). I start the coast at about 11-12 mph as I turn in at the top of a hard-for-me hill. Same tires, pressure, and it's me on the same bike.

How tall are you? How tall is the other rider? If you're taller then you'll be slower for a given weight. Leg length is somewhat important here. For example I'm about 73 kg (160 lbs), 170 cm (5'7"), and my saddle-bb distance is 67 cm. It's very short because I have short legs. Therefore I present a smaller profile to the wind than someone the same height but with longer legs, and I present a much smaller profile than a tall skinny guy. Someone I race against is a foot / 30 cm taller than me and weighs within a couple pounds of me.

Is the other rider solo? Were they on a group ride? My Strava power is phenomenal in a group ride/race where I'm drafting. My real power is almost always similar in range, like 150-190w avg. Strava will underestimate my power in a group ride/race by 200-300w.

Drops is not the fastest - you can pick up some speed (not 20 kph, but maybe 5-10 kph initially) by using an aero tuck. Hands near stem, head way over front wheel (if you're shorter on the bike like me) or resting thigh on top tube and keeping your torso just above the top tube (if you're taller).

If you go over the top of the hill faster you will hit much higher speeds. If the other rider sprints they'll hit much higher speeds, even if he's coasting a lot after the sprint. If you hit the steepest parts faster you'll have more time accelerating at the higher speeds (it's quick to accelerate from 20 to 30 kph, less so from 70 to 75 kph), and if you're already at top speed, you'll maintain it longer.

On a downhill, when I'm trying to put power to the pedals, I'm spiking my power to 800-1000w. I don't do that intentionally, I'm just trying to accelerate here and there while at speed, then returning back to a tuck. The power spikes really help push the speed up. 400w is not going to contribute a lot on a shallow descent.

Cornering, if there are corners. If you're not cornering well then you'll lose tons of speed. Maintaining momentum can really help push speeds up on a descent.
Thanks for your answer.

I can eliminate some factors. he is using a power meter, not strava. I think I have reached terminal velocity because my speed would be steady for a while before the bottom of the hill.

I think that leaves riding in a group, power under reporting (which means he's heavier), he's using deep wheels, and aero tuck. I don't think it's the tuck though, it's a twisty descend, it wouldn't be a good idea with cars and other riders.
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Old 05-19-15, 08:01 AM
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Originally Posted by greenlight149 View Post
Thanks for your answer.

I can eliminate some factors. he is using a power meter, not strava. I think I have reached terminal velocity because my speed would be steady for a while before the bottom of the hill.

I think that leaves riding in a group, power under reporting (which means he's heavier), he's using deep wheels, and aero tuck. I don't think it's the tuck though, it's a twisty descend, it wouldn't be a good idea with cars and other riders.
If it's twisty just curvy then no issues with a group/cars/etc. If it's twisty like 180 hairpins that you have to slow to 15-25 mph then then he might be going faster through the turns before the terminal velocity bit (which I assume is pretty straight?). This would give him some additional speed going into the straight/s.

If you can compare speeds and they look about the same in the turns then he's much more aero than you. It could be drafting - that's huge. It could be aero equipment, not as huge but worth a few mph. It could be that he's more dense than you, meaning in terms of kg per unit of air resistance. I'm very dense (lol) and so I generally descend pretty well. When I lost substantial weight (close to 40 lbs) I found I lost some of my descending prowess and had to do a lot more pedaling to maintain speeds with riders I normally out-descend just by coasting and tucking (like a friend/teammate that I'd ridden with for 20-odd years).
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Old 05-19-15, 08:41 AM
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If you follow pros on Strava you'll notice that they go super fast on descents, and they aren't heavy guys. Technique has a lot to do with it. They're comfortable going fast and aren't afraid to get in a full aero tuck.

On a twisty descent like you mention, the amount of speed you can maintain in the corners is critical. The fast/ballsy guys zoom through the corners and keep building up speed throughout the descent. The slow/wimpy guys like me ease up in the corners and are constantly regaining the speed that was lost.
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Old 05-19-15, 10:07 AM
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Aero and choice of line is everything in descents. He's probably doing considerably better than you on both fronts.
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Old 05-19-15, 10:12 AM
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The other guy must have ceramic bearings.
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Old 05-19-15, 11:06 AM
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IMO it's a waste of time trying to compare one's performance with another when access to all the data necessary is not available. just give someone a few hundred yards headstart and see where you stand at the top. it's a much more accurate way to assess one's performance relative to another.
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Old 05-19-15, 11:24 AM
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Almost certainly drafting something. Maybe a faired recumbent? Yes, foolish to compare unless you're riding with someone. The watts simply aren't there to find another 20kph.
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Old 05-19-15, 11:51 AM
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any combination of these:

- before descending he is adding some rocks into his shirt pocket and water bottles.
- maybe he has a more aero wheels and bike, combined with a better aero tuck
- are there turns and twists on the downhill? perhaps he is better at maintaining speed through the corners.
- perhaps on the crest of the hill he is pedaling to get a "running start".
- You have too much leg hair
- better tires / different air pressure in the tires.
- his wheels are the incorrect size in his bike computer
- he is using a stupid phone app that is always off.
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Old 05-19-15, 12:09 PM
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Originally Posted by Darth Steele View Post
any combination of these:

- before descending he is adding some rocks into his shirt pocket and water bottles.
- maybe he has a more aero wheels and bike, combined with a better aero tuck
- are there turns and twists on the downhill? perhaps he is better at maintaining speed through the corners.
- perhaps on the crest of the hill he is pedaling to get a "running start".
- You have too much leg hair
- better tires / different air pressure in the tires.
- his wheels are the incorrect size in his bike computer
- he is using a stupid phone app that is always off.
It's the leg hair, I have lots of it
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Old 05-19-15, 01:47 PM
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ask him and watch him ride.
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Old 05-19-15, 02:03 PM
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Digital EPO.
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Old 05-19-15, 03:49 PM
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Most likely just a difference in wind. You had a headwind and he had a tailwind.
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Old 05-19-15, 10:07 PM
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Originally Posted by Lazy Dog View Post
The other guy must have ceramic bearings.
And/or a red bike.
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Old 05-19-15, 10:50 PM
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does he have disc brakes?

I heard they're everything,,,and a bag of chips!
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