Not convinced

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  • Not convinced
  • wobbem
    Member

    Doesn’t quite add up in my view πŸ˜•

    [video]http://www.youtube.com/watch?feature=player_embedded&v=O-WN8kPolug[/video]

    Premier Icon firestarter
    Subscriber

    Some said the same regarding disc brakes tho πŸ˜‰

    L shaped cranks have been done before haven’t they?

    Premier Icon nickjb
    Subscriber

    P.M.P. “L” or “bent” cranks of the early 1980’s may be one of the most famous bad ideas in cycling.

    http://pardo.net/bike/pic/mobi/d.pmp-cranks/index.html

    Premier Icon oldnpastit
    Subscriber

    Uhhh, so if I want to increase the torque I have to increase the length of my cranks? Can’t I just change gear?

    perthmtb
    Member

    I don’t trust anyone who doesn’t look me in the eye when they’re talking to me, let alone not open them for the whole of the video. In fact, does that guy even have eyes? 😯

    b r
    Member

    Some said the same regarding disc brakes tho

    My Dad use to sell cars in the 60’s, and when discs started to come in folk would say they were dangerous because cars behind would run into you as their brakes weren’t as good… πŸ™„

    martinhurton
    Member

    The only think I’m not convinced about is the pedal being ahead of the crank when at tdc, which I agree will be beneficial when starting the power phase of the stroke but…that means when the pedal is at TDC the crank will be behind, which would not be beneficial.

    Premier Icon aracer
    Subscriber

    Why all the cynicism? Wouldn’t you like more leverage, and to get rid of the dead spots?

    nealglover
    Member

    My Dad use to sell cars in the 60’s, and when discs started to come in folk would say they were dangerous because cars behind would run into you as their brakes weren’t as good…

    To be fair, there is a decent bit of logic in that ?

    (I think)

    Gunz
    Member

    Can’t access the video but surely the torque produced by those cranks is exactly the same as if you just had a normal crank, from my A’ Level physics it’s the turning moment around a single point regardless of how many twists and turns you have in between.
    Can a proper engineer please explain.

    wobbem
    Member

    Can’t access the video but surely the torque produced by those cranks is exactly the same as if you just had a normal crank, from my A’ Level physics it’s the turning moment around a single point regardless of how many twists and turns you have in between.
    Can a proper engineer please explain.

    My thoughts as well

    Premier Icon firestarter
    Subscriber

    Without watching the vid as I’m on my phone, I think they are trying to eliminate the dead spot but I think all they have achieved is to have moved it .but there is a reason I joined the army straight from school and my grasp of engineering wasn’t it πŸ˜‰

    andy7t2
    Member

    does this mean that your crank arm will be closer to the ground at the bottom of the stroke and more likely to catch the floor

    michaelmcc
    Member

    In English please Martinhurtin? πŸ™‚

    bencooper
    Member

    They’re very clever – the angle of the crank has been carefully optimised to be the perfect angle to separate idiots from their money.

    messiah
    Member

    Excellent find trail_rat… 8)

    martinhurton
    Member

    These z cranks look to be different to the L cranks that others are posting.

    The crank length is longer so increasing torque, then they’ve used the bend to bring the pedal back in, to give the same pedalling diameter as a shorter arm. So you have a longer crank arm distance from the bb without the increased pedal diameter.

    All of the cranks in the article above haven’t increased the length from the bottom bracket to the outside of the pedal circle, so they have maintained the same stroke diameter (pedal the same distance from the bb) so the torque applied won’t have changed.

    I think they would work.

    trail_rat
    Member

    but if that WAS true what advantage does it give over changing gears ? or fitting 180mm cranks ?

    rusty90
    Member

    you have a longer crank arm distance from the bb without the increased pedal diameter.

    So the pedal’s further away from the BB, giving greater torque, but also the same distance away from the BB, keeping the pedal diameter the same as a normal crank. Gosh that’s clever.
    (This reply may contain sarcasm)

    GCSE level physics fail! Like getting a bigger spanner and then putting your hand only 3/4 of the way along it to reduce your arm movement…

    ac282
    Member

    trial rat posted a great explanation of why this is rubbish. They are for the hard of thinking.

    rusty90
    Member

    Why bother with L-shaped cranks when you can have perpetual motion ones?

    nigelb001
    Member

    Ye canna change the laws of physics!

    andrewh
    Member

    Spent ages to trying to figiure out how they worked.
    Then realised that there are two in the picture and it isn’t really that shape!
    .

    The crank length is longer so increasing torque, then they’ve used the bend to bring the pedal back in, to give the same pedalling diameter as a shorter arm. So you have a longer crank arm distance from the bb without the increased pedal diameter.

    Yes, the crank is longer but the BB to pedal distance is the same. Am I mising something? Is lever length inmportant or is just force-to-pivot distance in a straight line which matters?

    Pieface
    Member

    But any torque gains in the crank will be lost through the square taper interface

    rusty90
    Member

    Yes, but he’s compensated for that by having a large letter Z on the side – in red!
    Z is the 2nd fastest letter in the alphabet (X being faster, obviously) and red is the fastest colour there is.

    Premier Icon igm
    Subscriber

    If they flexed through the stroke altering the effectively crank length through the stroke then something might happen.

    But

    A) not much; and
    B) probably not something helpful

    johnellison
    Member

    Absolutely no advantage to them whatsoever. The point at which force is applied is still only 165/170/175mm from the bottom bracket spindle no matter how much material you add or take away.

    Plus I suspect that they would be prone to catastrophic failure given the enormous stress-riser in the “vee”.

    Close the thread.

    brakes
    Member

    this can only be bollocks.
    the only advantage that I can see is that it may eliminate the dead spot at the top of the stroke IF (and that’s a BIG IF) you are thinking that you are at the top of the stroke when the longer bit of the ‘L’ is at the top and not where your pedal is… but when I think about it for too long, who is going to do that? and it’s therefore a psychological effect rather than a mechanical one.

    globalti
    Member

    Spot on. The important length is the virtual length of the crank; it could be five feet long coiled up like a watch spring but the leverage on the BB axle would be exactly the same.

    maxtorque
    Member

    I think those cranks ilustrate precisely why Engineering should be left to actual Engineers, and not people in Marketing………….. πŸ˜‰

    Premier Icon oldnpastit
    Subscriber

    Even longer cranks, so even more torque right?

    (Some Biopace chainrings on those would be totally amazeballs!).

    trail_rat
    Member

    boy says they did testing at wise univeristy florida .

    by some PHD folks some 10 riders used them in TT and hill climbs….. and reported 20% gains.

    once again like my honours project – bullshit baffles brains.

    Premier Icon Cheezpleez
    Subscriber

    @Oldandpastit – are those for real? What about a sprung spiral to provide suspension when stood on the pedals?

    Premier Icon andytherocketeer
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    Must the extra springiness of the bent cranks that store up energy on the down stroke and then give it back on the upstroke, or some such BS. So the energy/torque loss in 1 phase gets magically amplified and returned 180degrees later making it 20% more efficient.

    (edit: some πŸ˜‰ πŸ˜‰ πŸ˜‰ are needed here)

    I have a pair of Biopace rings if someone wants to enhance the cranks even more.

    pdw
    Member

    Last time we dismissed this in 13 posts. Can’t believe we’re up to 37 this time around…

    http://singletrackworld.com/forum/topic/using-the-concepts-of-leverage-and-inertia

    Premier Icon oldnpastit
    Subscriber

    A sprung spiral would be even better – the effective length would be even longer so the torque would be that much greater. There would be virtually no hill you could no ride up. That together with the suspension effect you identify would make this ideal for mountain bikers.

    (This post may contain sarcasm).

    rusty90
    Member

    How about fractal cranks, giving you an effective crank length of infinity?
    Or hyper-cranks, that exist in 4 dimensions instead of the usual 3?
    This guy is just so 19th century in his outlook.

Viewing 40 posts - 1 through 40 (of 63 total)

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