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  • Are less teeth more efficient?
  • Premier Icon epicyclo
    Full Member

    When I were a lad, just after the last dinosaur died, and before the derailleur epidemic, there were still quite a few riders on path race bikes using gap tooth chains.

    Inch pitch chainring

    The riding gods told us this was more efficient.

    Naturally callow youths, such as I was then, could not afford such exotica.

    So when we weren’t drilling holes in steel components with a handheld drill (pre-electric) we mimicked the fancy chainrings by filing off every second tooth on our chainrings with the blunt rusty file from the shed.

    Only to be disappointed that we didn’t gain the expected increase of 10mph velocity.

    As a consolation we comforted ourselves with the thought of all the weight saved, and how the handbrushed red (or yellow) paint job made the bike look like a real racer rather than grandad’s commuter.

    So here I am many years later tempted to build up a bike like I used to build back then, only using modern tools – just think what a Dremel could do to a chainring. Or the myriad of holes as an old Dreadnought gets Swiss Cheesed with a cordless drill and HSS bits.

    So the big question: Is there actually an gain in efficiency by removing every second tooth on a chainring? (I doubt it, but if so, that extra half watt of efficiency would be put to good use.)

    There is a tin of blood red red paint and brush ready for the period paintjob.

    Such is the Lockdown induced madness… 🙂

    Premier Icon paton
    Free Member
    Premier Icon thols2
    Free Member

    Apparently, most of the friction comes from the links bending around the sprockets, so a larger sprocket means less friction. Cutting out half the teeth won’t make any difference to that.

    Premier Icon tthew
    Full Member

    There is a tin of blood red red paint and brush ready for the period paintjob.

    Presumably blood red was chosen for hiding actual claret when the inevitable outcome of drilling loads of holes in load bearing components occurs?

    Can I have your, (other) bikes?

    Premier Icon RustyNissanPrairie
    Full Member

    A small amount of friction comes from the inner chain roller riding up and down the tooth profile – removing every other tooth will halve that friction with the sprocket but will result in the remaining tooth/roller interfaces having double the loading. My tiny brain can’t decide if the friction between the roller riding the tooth face is more or less than doubling the load on the remaining rollers/teeth.

    Premier Icon FB-ATB
    Full Member

    Golf balls are dimpled for aerodynamics. So I’d set to the bike with a ball pein hammer first. Don’t forget to set the camera rolling.

    Premier Icon epicyclo
    Full Member

    tthew
    Presumably blood red was chosen for hiding actual claret when the inevitable outcome of drilling loads of holes in load bearing components occurs?

    Can I have your, (other) bikes?

    Never managed to break one, but probaly because the old bikes were built out of recycled battleships or something similar.

    I was never as brave with Drillium as Eddie Merckx though…

    Premier Icon kerley
    Free Member

    Apparently, most of the friction comes from the links bending around the sprockets, so a larger sprocket means less friction.

    Plus is sounds smoother/less noisy especially as rear cog increases. If anyone has ridden a BMX with a 9t driver at the back you will know how rough they feel. I use a 19t at the back and it is very smooth but can’t say it has made much difference to my Strava times!

    Premier Icon thecaptain
    Free Member

    I would say not, my dad was struggling with a decent steak in his later years.

    Premier Icon Greybeard
    Full Member

    my dad was struggling with a decent steak in his later years

    But the question was efficiency, not effectiveness. I have about 2/3 of my teeth left after 65 years, but I think I can chew 90% as well as I ever did – so in terms of performance per tooth, my teeth are more efficient.

    Premier Icon molgrips
    Full Member

    My tiny brain can’t decide if the friction between the roller riding the tooth face is more or less than doubling the load on the remaining rollers/teeth.

    I think dry friction is proportional to pressure – and with the same force going through half as many rollers (i.e. half the area) the pressure would be twice as much, cancelling out the gains.

    However we lubricate our chains with oil (most of us!) which gets squeezed out under pressure, so you’d probably have a better film of oil (and more lubricity) if you had more area which suggests that it’d be more efficient overall to have more teeth in contact, not less.

    Premier Icon epicyclo
    Full Member

    On reflection, I’m pretty sure if Shimano chainrings would be missing every second tooth if there was an advantage, they’re pretty canny.

    But, but, surely the riding gods of my youth on their Flying Scots couldn’t have been wrong?

    I’m off to crack a bottle of Hogmanay juice* to relieve the wave of disillusion and prepare for 2021.

    *12 year Glen Ord single malt Singleton (what else would a SSer drink? 🙂 )

    Slainte to all STWers, and may 2021 bring us all joy.

    Premier Icon thols2
    Free Member

    On reflection, I’m pretty sure if Shimano chainrings would be missing every second tooth if there was an advantage, they’re pretty canny.

    There’d be half as much metal to wear away so they’d wear out twice as fast (possibly faster).

    Premier Icon Northwind
    Full Member

    The John Hopkins study is all with new, clean chains so I’m not sure how useful it really is (they acknowledge the limitations themselves in the article)

    For sure there’s some friction on the teeth and in principle lubrication should reduce that. But, the amount of friction is tiny. You can tell it’s tiny, because you have steel wearing on either thin steel or aluminium, and if the level of abrasion wasn’t tiny then the lifespans would be short. It really doesn’t take a lot of material loss to stop a chainring from working- especially so with narrow-wides.

    Less teeth would mean more pressure on the teeth that remain, but it’s got to be a pretty complex relationship. I suppose the other thing is that a worn ring might not be equally efficient as a less worn ring and the ring with less teeth will probably wear faster. (Maybe the worn ring would be more efficient? Matched wear with the chain after all)

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