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Old 06-03-09, 09:04 AM   #1
Doggus
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Downhill power

it hurts me.

I haven't figured out why, when the road turns slightly south, it gets very hard to maintain the power level I'm working at.

I've also noticed, when the road goes up it's very 'easy' to maintain a steady, higher power number.

I have a road that I use to do anything 5-10 minutes in length. I hate the parts on that road that go downhill. It's only a slight downhill but I always have to 'recover' from those when I hit the flat and start pacing it again.

My cadence will increase on the downhills until I grab enough gears that I'm back to optimal but it is still an effort to try and stay in the range until it flattens out or goes up.

Different muscles in use here? What's the explanation?
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Old 06-03-09, 09:07 AM   #2
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Power = torque * angular velocity

when your speed increases as much as it does on a downhill you can't put out the same torque like if you were cranking it up hill in a low gear providing massive torque at a lower speed. it is a balance though. there will be a certain speed when it starts to decline.
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Old 06-03-09, 09:36 AM   #3
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This is one reason I like to have a 53x11. It allows me to keep steadier power on downhills when training.
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Old 06-03-09, 06:32 PM   #4
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When I first got my PM I was amazed by how little work I was doing downhill. It was a big wake up call to push harder once I'd crested hills. It's really helped in my training.
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Old 06-03-09, 06:45 PM   #5
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I think its a mental thing.

"I'm already going fast, why do I need to pedal hard again?"
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Old 06-03-09, 06:52 PM   #6
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Assuming you have appropriate gearing, it's the inertia problem. On a climb, your speed loss during the weak part of the stroke is much more linear. On a descent, it's quadratic, since your wind drag (force) is proportional to the square of your velocity (e.g. you're not fighting much wind on a climb).

I think the resulting power surges take the edge off your FTP.

So, on a descent, your mid-stroke acceleration and deceleration is MUCH greater, and you're wasting more energy getting your leg speed back up (accerating the bike into quadratic resistance) every revolution.

This is the same reason trainers sap more power than when you're on the road, and why flywheel ergometers don't (think of the coast-down time on the road vs. on a mag trainer).

It's tough to fight the power problem, but it can help the speed to sprint over the crest a bit and get back up to a high speed as soon as possible (spending as little time going slow as possible).
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Old 06-03-09, 08:59 PM   #7
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Are you a small guy by chance? Maybe you don't get much help from gravity and have to do it by yourself.
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Old 06-03-09, 09:01 PM   #8
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I think its a mental thing.

"I'm already going fast, why do I need to pedal hard again?"
no
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Old 06-03-09, 09:30 PM   #9
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Are you a small guy by chance? Maybe you don't get much help from gravity and have to do it by yourself.
That makes no sense. This is about downhill power, not speed
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Old 06-03-09, 10:34 PM   #10
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I'm glad I don't have this problem. Downhills and false flats have always been my salvation
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Old 06-03-09, 10:50 PM   #11
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Doggus is most definitely not a small guy.

Doggus I think you could work on core strength and spinning drills. Just a hunch.
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Old 06-04-09, 05:52 AM   #12
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Seriously though, it's the same reason trainers kill off some power. You can't train this away. All you can do is suffer through it.

On our local TT loop, I am more beat from pushing 98% down the big hill than I am from pushing 115% up it.
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Old 06-04-09, 05:59 AM   #13
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That makes no sense. This is about downhill power, not speed
bingo.


get yourself an 11 and keep on pushing.

I have a 12, but generally can push threshold power on all TT descents except ones that have me at 45mph or faster.

NOW if my threshold was 100 watts higher like I want it to be, then maybe that would be tougher, but I could get the 11 then.
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