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  • E-Bike press release Kool Aid
  • richmtb
    Full Member

    From the Sram E groupset article on the main page

    Someone needs to work on their understanding of torque and gear ratios because this is nonsense

    Look at your cassette. Down at the bottom you have 11 then 13 teeth – a 2 step difference. At the other end on the big rings you can jump from 36 to 44, because at this end your legs will be pushing high torque at higher RPM so you can deal with the big jump in teeth. If you look at the profile of your cassette you’ll see it’s a curve. Power output from your legs is not linear and so this curve in the cassette profile kind of matches what your legs can do. There are lots of variables and lots of riders ride their bikes in different ways but the important thing to note is that fact that the human body puts out different amounts of torque at different RPM.

    The difference in ratios between one gear and the next is linear – or as close as it can be given that sprockets need to be whole numbers.

    11 speed 10-42 cassette 10-12-14-16-18-21-24-28-32-36-42

    12-14 is a 17% jump. 36 to 42 is also a 17% jump

    8 speed 11-48 “e-cassette” 11, 13, 15, 18, 24, 32, 40, 48

    11-13 is an 18% jump 40 to 48 is a 20% jump

    Car gearing – with a lot more power than a Bosch electric motor – works exactly the same

    Also torque?

    You have the same amount of torque available at the cranks regardless of the gear you are in its the maximum force your leg muscles can produce in Newtons multiplied by the length of the crank arm in metres. Torque at the back tyre does vary based upon the mechanical ratio you are getting from the gears but it doesn’t really have anything to do with the amount of torque a rider can produce at the cranks

    scaredypants
    Full Member

    people read that shit ? 😯

    Rubber_Buccaneer
    Full Member

    Who wrote that, it’s the sort of utter bollocks I expect in MBR?

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    thisisnotaspoon
    Free Member

    Cassette aside, there is a point even if the copywriter has completely missed it when the mechanical engineer tried to explain it to him/her.

    On a steep techy section you’re spinning, but what you really want is a sudden burst of power to get over something and you can’t do that, your legs produce near enough constant power and can’t produce that much torque at high RPM. An electric motor on the other hand produces a relatively flat torque curve from near enough zero to it’s max. So it can give that boost when it’s actually needed.

    So climb an e-bike in a higher gear, and let the motor take the strain, then you’ve got enough RPM left in your legs to get it over something rough.

    Rubber_Buccaneer
    Full Member

    You have diesel legs tinas 🙂 but you do have a point.

    thisisnotaspoon
    Free Member

    Think it’s more like e-bikes are a turbo diesel. You go up hill with the turbo whirring away giving torque and therefore power at low RPM, then when you hit a loose bit you can accelerate because you’re not already redlining.

    The opposite of trying to climb a steep hill on an under powered 2-stroke motorbike, you try to keep it in the power band, but that leaves no margin for slowing down or speeding up.

    On a related note saw a chubby kid (~11?) on an expensive e-bike the other day.

    Fair enough, it allows him to keep up with dad and dad’s mates on a longer ride.

    Dad and dad’s mate were also on e-bikes. Despaired 🙁

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