Why is it sooo hard to keep watts up on downhills?

Discussion in 'Power Training' started by Smart1, Jul 10, 2018.

  1. Smart1

    Smart1 New Member

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    During my VO2max intervals today i came to some downhills at maybe 4% and with a headwind. i had to go 100% effort just to keep my watts near my targeted zone. as soon as the road leveled off, my preceived exertion was much lower with power in the same zone. then i hit a moderate upgrade and it's a piece of cake to hold the power in target zone. my cadence was relatively the same, slightly lower on the climbs.

    anybody want to explain this?
     
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  2. Power Meter City

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    Yes indeed. This is the case for the majority of us. The neurological demands of generating power at speed/higher wind resistance is just way different. It's why in a race situation, you're better off trying to get aero at high speeds vs. trying to turn out the watts (assuming you don't run out of gears). But in any event, I definitely try to avoid descents when doing intervals! :)
     
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  3. sell4bids

    sell4bids New Member

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  4. svejorange

    svejorange New Member

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    Nice question it indicates your focus on the subject!
     
  5. swampy1970

    swampy1970 Well-Known Member

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    It feels like this because you probably didn’t go so hard on the downhills before. There’s probably a few factors going on here but the couple that always got me when I wasn’t really fit were:

    Going from slow speed, high torque effort on the uphills to high speed, low torque and lots of momentum on the downhill. Whack it into the biggest gear you have and see if that helps. If you’re already in the biggest gear you have then there are two options - train more on the same roads and see if it improves or just get a bigger top gear. As you transition your effort from uphill to downhill use the gears more rather than adjusting your pedaling speed quickly - unless you’re really fit and are used to that effort.

    Mentally it’s a mindf*** to have to pedal that hard on a downhill. If you race lots in the hills then you may be used to 666% efforts coming out of most corners if someone’s on the attack but for most folks the brain doesn’t equate downhills to being a lot of work.

    The other part of this quandary may be that you’re not used to pedaling that fast. If you’re outside the rpm range that you’re used too then you’ll be feeling the effort more than you normally would.
     
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  6. alfeng

    alfeng Well-Known Member

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    GRAVITY, plain and simple, is a significant, quantifiable factor which will affect the number of Watts needed to traverse the course you are riding along ...

    Gravity affects WORK ...

    Whether going UPHILL or DOWNHILL ...

    Even on a level surface because the rolling resistance may be affected ... ​

    Someone more inspired than I am can calculate how much Gravity is adding to the diminished amount of Work you need based on the combined weight of the rider+bike compared with the Work you input to go uphill OR along a level surface ... presuming OTHER Factors are the same (e.g. rolling resistance, wind resistance, etc.) ....


     
  7. swampy1970

    swampy1970 Well-Known Member

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    I see you still miss the point on what people are asking. Maybe the empty gap between the ears is bigger than the Camapg hirth joint in a failed crank install.

    The OP asked why is it harder to put out X watts going down hill than anywhere else. A watt is a watt, so in theory, it should be just as hard to put out 300 watts on a 3% downhill as it is on a 3% uphill. The reality is, this isn't the case. Gravity effects the speed but it shouldn't make it harder to put out the same effort.

    We're all used to riding hard up hill and quite often on the flat but not many are used to race efforts on downhills for an extended period. The effort is much different. In a similar way, I can put out over 1,000 watts in a short effort on a climb but ask me to do that on the flat after coming off a wheel or out of the slipstream of a car at 50kmh and there'd be no way.

    Maybe I should get the wife to take her bike license so she can ride the S1000RR and give me sprint training but the thought of my motorcycle being in first gear for a long time pains me plus the throttle control to accelerate that slowly on that bike would be tricky for a n00b. :eek::D
     
  8. alfeng

    alfeng Well-Known Member

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    OMG!

    YOU must have been drinking some of Bob-Error-Man's koolaid ...

    Without getting into the weeds ...

    If YOU-or-any-of-your-"engineeer"-friends calculate how many watts are need for a bike-and-rider to ascend a particular height over a particular distance then THAT will be a baseline for the requisite amount of Watts needed to be added to the descent over a comparable distance & elevation change ...

    Kinetic energy becomes potential energy at the crest of the hill ...

    In other words, instead of inputting the coefficient of friction for the "work" being performed, we should be able to substitute the effects of Gravity in whatever manner YOU choose to calculate it.
    So, to achieve a similar wattage going downhill the rider would need to achieve a speed whereby s/he overcomes (ADDS TO) the converted kinetic energy (i.e., potential energy) used to ascend IN ADDITION TO the hoped for wattage ...

    The OP can install a "drag brake" on his bike if he wants to add wattage to his descents.

    Verstehen Sie?
     
    #8 alfeng, Jan 19, 2019
    Last edited: Jan 19, 2019
  9. swampy1970

    swampy1970 Well-Known Member

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    Who would want to drag brakes going downhill so that their power meter read more watts? That’s as stupid as your reasoning. Said no one ever: “man, I was putting 400watts out on that last descent but he just rode away from me because I had my brakes on the whole way down.”

    The deal is the poster wants to put out the same number of watts as they can on the uphills but is challenged in this department and wants to know why. He probably wants to drag brake as much as they want their significant other to drag teeth during some late night fun.

    Many riders have a problem hitting the same numbers downhill and you just have to get used to pedaling that hard and fast as it’s something that most are not used too. Unless you’re the donkey and the carrot is riding off up the road, it’s hard to mentally put out that kind of power downhill as for many the brain say “downhill - time to take it easy” and when you do gas it, the legs aren’t used to putting out threshold power in that kind of gear at those rpms. It requires mental and physical training and less dragging brake.
     
  10. alfeng

    alfeng Well-Known Member

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    Sheesh ...

    You really have to take-the-needle-out-of-your-arm ...

    The POINT was that the OP of this thread (who cut-and-pasted the SAME query POSTED BY velomanct (Mar 14, 2004)!) cannot realistically* achieve a comparable number of Watts while going downhill WITHOUT the addition of something which would add "Work" to the effort.
    Can YOU achieve the same number of Watts while going downhill?!?


    * Oh, I suppose that using something like a 62t-or-larger Chainring + 11t Cog might provide sufficient "Work" which would result in MORE Watts.


     
    #10 alfeng, Jan 22, 2019
    Last edited: Jan 22, 2019
  11. swampy1970

    swampy1970 Well-Known Member

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    A watt is a watt. It’s the measure of the work done.

    The OP can produce the required work but only with greatly increased perceived effort. I could do it when fit but it took training to become more used to it and to make the perceived effort seem more reasonable.

    While a bigger chainring and a smaller cog is an option, it’s one that is rarely taken. Why? Maybe people mentally perceive that a 53x11 is bigger than what’s needed instead of thinking “what gear do I need to do X rpms at Y mph.” Especially in an aero tuck on a TT bike, if you have sections where you are going to be going over 40mph, think about bigger gears.
     
  12. RapDaddyo

    RapDaddyo Active Member

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    I can relate to the OP's question because I feel the same way, which is that it takes more effort to do my high-intensity efforts on downhill and/or downwind road segments. What I mean by more effort is more concentration rather than more physical exertion. I attribute this phenomenon to the fact that the bike accelerates too easily and quickly with less resistance. When possible, I always choose uphill and/or upwind road segments for my high intensity efforts. I simply find that it takes less concentration to ride at my target power with greater resistance. And, btw, I have considered building a power meter computer-driven disk brake controller to apply resistance artificially for training rides.
     
  13. audreyspency

    audreyspency New Member

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    Yes indeed. This is the case for the majority of us. The neurological demands of generating power at speed/higher
     
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