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  • Physics of riding bikes in hills question?
  • Premier Icon joemarshall
    Free Member

    Okay, this is a stupid question which I’m sure if I thought about it long enough would be obvious.

    If you’re riding (on road) a hilly route, assuming you have a fixed amount of energy to use up, is it faster to:
    a)Ride at constant effort all the time
    b)Ride hard up the hills, coast down the hills.

    My instinct tells me that (b) is likely to be faster, because higher wind resistance means the extra effort on downhills is more wasted. But my brain is failing when I try to do the maths.

    All ignoring the fact that I can tuck deeper without pedalling which on some hills means a faster overall speed – I managed more than 60km/h on a hill that I usually hit 55 on the other day, just by hammering it over the top, then tucking as it gets steep.

    I think it might also depend on the profile of the route – what I really want is a tool that takes a load of variables like weight / power / frontal area etc., and the route profile for my route and then simulates it.

    Premier Icon HoratioHufnagel
    Free Member

    more efficient going fast as possible up the hills due to air resistance being non-linear.

    This is usually the advice given in time trials too.

    Premier Icon rhyswilliams3
    Full Member

    Depends on the route, and how steep said hills are. All good and well coasting down a ‘tour hill but it’d take forever if there was a hill with hardly any gradient.

    Premier Icon TiRed
    Free Member

    Riding with gears and coasting down the hills is a lot more efficient than riding fixed. I’ve done both. Fixed, however is the better workout.

    Premier Icon joemarshall
    Free Member

    more efficient going fast as possible up the hills due to air resistance being non-linear.

    Great, that was my guess, but somehow, perhaps through years of riding fixed gear and unicycles, it always feels right just to keep spinning the pedals round all the time.

    Hopefully it’ll save me time (or energy) on the commute, especially when combined with the fact that I’ve been doing tons of swimming, so I have a way stronger and more flexible back, so can get in a low tuck much more easily.

    Premier Icon joemarshall
    Free Member

    If I had googled more effectively I might have found this:

    http://www.trainingbible.com/joesblog/2009/05/more-on-time-trial-pacing.html

    Premier Icon aracer
    Free Member

    more efficient going fast as possible up the hills due to air resistance being non-linear.

    This is usually the advice given in time trials too.

    Except it isn’t the advice given by a certain chap called Chris Boardman. His pacing advice is not to go flat out on the climbs and save something so you can press on on the descents – he seems to have done OK despite not following your suggestion. Yes you want to go a bit harder on the climb, but it obviously depends on the course – if the descent is technical not a lot of point saving energy for it, however if it’s fairly straight and you can put in a bit of effort then it’s worth doing so. See the TdF TT a couple of days ago where Froome won it on the descent.

    Premier Icon no_eyed_deer
    Free Member

    ^ this is partly sports physiology though

    …on a pure physics basis HoratioHufnagel has it

    Premier Icon joemarshall
    Free Member

    Right, I have been experimenting, and maybe it is just psychology because I feel faster, but even in my not super fit state of the moment, I am 5 minutes faster over 16 hilly miles by attacking the hills and chilling out on the descents, as opposed to constantly slogging. 57 minutes today, I also don’t feel as knackered when I get in.

    Result.

    Premier Icon Dales_rider
    Free Member

    Personally I’d say improve on all counts, most people put max effort into riding up hills but on the flat are happy to cruise. Downhilling just watch the video on Cancellaras descent, which put him back in the race.

    Premier Icon joemarshall
    Free Member

    Downhilling just watch the video on Cancellaras descent, which put him back in the race.

    I suspect the TDF is pretty irrelevant to my commute though, for a bunch of reasons:
    a)Tour de France riders have a lot more energy than me.
    b)TDF riders are often limited by terrain as to how much effort they can put in on some sections (downhills mainly).
    c)TDF riders are limited by drafting as to how much effort it is worth putting in on the flat. Unless they’re going for an attack or trying to push the pace for tactical reasons, what is the point in powering hard in the peleton?
    d)In the TDF, there’s a massive advantage in putting hard power in at some points in order to catch up with someone else for drafting.

    Whereas right now I am a not that fit 2 days a week commuter, very rarely riding at a speed where terrain is what stops me going faster (I can think of one corner on my commute where I can physically get myself fast enough that I’d have to slow myself down for the corner. So essentially I have a total amount of energy to put in over the ride, and can choose whether I expend that energy in downhills, on the flat, or on uphills, and how I balance it. And it seems to me that if I put in minimal effort in the steeper downhills, I don’t lose much speed overall on the downhills, and can keep it pretty much always over 20km/h on the uphills. And 17mph (actual, not riding time) average despite being pretty unfit is not to be sniffed at, is a fair bit better than any rides this year before I started doing this.

    Premier Icon Dales_rider
    Free Member

    So you have answered your ownn question

    Thread closed

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