Weird cranks on Ebay

Mike400
Mike400 Posts: 226
edited May 2010 in Commuting chat
Noticed these when I was browsing cranksets:

http://cgi.ebay.co.uk/NO-UPPER-DEAD-POI ... 3eff7e0ea8

Never seen anything like them before!
twitter @fat_cyclist

Comments

  • UndercoverElephant
    UndercoverElephant Posts: 5,796
    Look like an updated version of the PMP cranks:

    http://www.classicrendezvous.com/Italy/PMP_main.htm

    I'm not sure whether they are cool or not. I think I like them though.
    Sun - Rain - Snow
  • will3
    will3 Posts: 2,173
    :lol::lol:

    apparently you have to lubricate them with snake oil.
  • Mike400
    Mike400 Posts: 226
    UndercoverElephant wrote:
    Look like an updated version of the PMP cranks:

    http://www.classicrendezvous.com/Italy/PMP_main.htm

    I'm not sure whether they are cool or not. I think I like them though.

    Cheers for that, interesting stuff. Must be a reason they were consigned to history though.
    will3 wrote:
    :lol::lol:

    apparently you have to lubricate them with snake oil.

    My initial thoughts, but when you actually think about it the theory makes sense. Whether they are any good in the real world is anyones guess.

    The cynic in me would look to the UCI regs to see if that killed them off?
    twitter @fat_cyclist
  • UndercoverElephant
    UndercoverElephant Posts: 5,796
    I'm not sure about the spiral ones, but I believe the thing that killed off the L-shaped ones was the fact they had to be longer and thus actually had more flex; allied to the fact that the PMP ones bent the wrong way to have their alleged improvement.

    I think it was more the lack of available horse-feather grease fr the installation which killed them off.
    Sun - Rain - Snow
  • jonginge
    jonginge Posts: 5,945
    I think they'd only work if the curved (or right-angled) bit was quite heavy so its momentum propelled the foot through the dead-spots... If that were the case they'd take a bit more effort to spin up.

    Effective or not, it's a good way to raise your bike above the UCI weight limit :P
    FCN 2-4 "Shut up legs", Jens Voigt
    Planet-x Scott
    Rides
  • will3
    will3 Posts: 2,173
    Mike400 wrote:

    My initial thoughts, but when you actually think about it the theory makes sense. Whether they are any good in the real world is anyones guess.

    ?
    Go on then, explain the theory in a way that makes sense.


    Or thjnk about it for a microsecond and realise it's very clearly bollox.
  • Agent57
    Agent57 Posts: 2,300
    I don't really see how they can make a different. I mean, the pedal spindle is still in line with the spindle of the other pedal, on a line going through the centre of the bottom bracket. It just seems to be exactly the same mechanism as a straight crank to me.
    MTB commuter / 531c commuter / CR1 Team 2009 / RockHopper Pro Disc / 10 mile PB: 25:52 (Jun 2014)
  • will3
    will3 Posts: 2,173
    JonGinge wrote:
    I think they'd only work if the curved (or right-angled) bit was quite heavy so its momentum propelled the foot through the dead-spots... If that were the case they'd take a bit more effort to spin up.
    :P

    That effect would be cancelled out exactly by the other crank.
    It doesn't matter what fancy route you take between the pedal and the chainwheel, the relative positions remain the same.
  • jonginge
    jonginge Posts: 5,945
    will3 wrote:
    JonGinge wrote:
    I think they'd only work if the curved (or right-angled) bit was quite heavy so its momentum propelled the foot through the dead-spots... If that were the case they'd take a bit more effort to spin up.
    :P

    That effect would be cancelled out exactly by the other crank.
    It doesn't matter what fancy route you take between the pedal and the chainwheel, the relative positions remain the same.
    Was hypothesising using conservation of angular momentum rather than PE converted to KE (and vice-versa) due to the mass of the crank falling (rising). My hypothesis was that during the power phase of the stroke the mass of the curved section is accelerated past the dead spot. At or near the dead-spot of the stroke the leg exerts little or no force. However, the crank already has inertia which would help speed the foot past the deadspot.

    This was pure hypothesis to try to explain why someone would design such a monstosity not because I believe it. I really don't think they would work either. :)
    FCN 2-4 "Shut up legs", Jens Voigt
    Planet-x Scott
    Rides
  • will3
    will3 Posts: 2,173
    JonGinge wrote:

    That effect would be cancelled out exactly by the other crank.
    It doesn't matter what fancy route you take between the pedal and the chainwheel, the relative positions remain the same.
    Was hypothesising using conservation of angular momentum rather than PE converted to KE (and vice-versa) due to the mass of the crank falling (rising). My hypothesis was that during the power phase of the stroke the mass of the curved section is accelerated past the dead spot. At or near the dead-spot of the stroke the leg exerts little or no force. However, the crank already has inertia which would help speed the foot past the deadspot.[/quote]

    Which you could achieve just by making really heavy cranks. Can't see a downside to that can you :lol: oh wait , you did see a downside.........
    JonGinge wrote:
    This was pure hypothesis to try to explain why someone would design such a monstosity not because I believe it. I really don't think they would work either. :)

    you will go far :wink:
  • Aidy
    Aidy Posts: 2,015
    Mike400 wrote:
    My initial thoughts, but when you actually think about it the theory makes sense. Whether they are any good in the real world is anyones guess.

    The cynic in me would look to the UCI regs to see if that killed them off?

    Meh.

    Thought experiment; Consider how the position of the pedal axles move in relation to the bottom bracket.

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