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I've just purchased a Cube Editor bike that uses the Gates CDX drivetrain. I was in between sizes and decided to go with the smaller one, but it looks like I may have made the wrong choice.

I'm using the bike with a front-mounted baby seat so I can't really get the seat much higher, which means I'm thinking of replacing the cranks with some longer ones (I think the ones installed are 170mm). However I haven't been able to find any original ones longer than 175mm.

Are there any aftermarket vendors that make Gates-compatible crank arms that would work on my bike?

Thanks in advance!

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    I go with oscu0's answer. From a bike-fit perspective, this is probably a bad idea for your riding ergonomics. However, (I think) you should be able to use any crank with matching BCD and bottom bracket standard... keep the chain ring, swap for a 175 mm crank.
    – DoNuT
    Nov 21, 2023 at 13:46

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Don't. This is a terrible idea. Saddle height must be absolutely correct, it is the most core bike fit adjustment. Even if you are able to fit huge cranks meant for 200cm+ people to your bike, it will ruin your pedaling biomechanics. You will need to bring your leg up very high on the upstroke, and longer cranks encourage cycling at a lower cadence, which is bad for your knees, doubly so with extra weight - like a child. It's commonly held these days that most people use excessively long cranks as is. If you are old enough to own a child seat you are old enough to have cause to take care of your joints - I'd look into a different child seat before trying to do what you are doing.

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    I agree it's a bad idea, but there's more flexibility in saddle height than you seem to think. Different fitters will put the saddle in a different place for the same rider. And when I ran a rear child seat, I put the saddle 1-2 cm lower than ideal, for stability when standing (you don't want to tilt the bike as much when you put a foot down with a child's weight up high). I only put it back up for quick rides of several 10s of km, leaving it low for all my commutes.
    – Chris H
    Nov 21, 2023 at 15:10
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This is pretty much why I didn't get a front child seat. Honestly I think for many rider/bike combinations that otherwise fit properly, these seats can only be used if you ride with your knees out to the sides. Or to keep your knees on a sensible line, you need a bike that's really a bit big for you - but standover height becomes very important with a child seat.

But you have another set of problems beyond your own bike fit, if you fit extra-long cranks:

  • Your knees will be more bent at the top of the stroke, putting them back near the seat again - so the long cranks might not even help much.
  • You're getting closer and closer to pedal strike. A fairly small bump in the ground when cornering can mean losing all your clearance (which is pretty small to start with). With a high load, recovering from pedal strike is harder, and that high load is very important.
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  • Very true. So far after fiddling with saddle height for a bit longer I got to a point that sortof works for me, but i'm still dealing with the flaring knees... oh well, guess i'll just have to wait it out until we move to a rear bike seat.
    – Tibi Neagu
    Dec 19, 2023 at 15:23

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