Bicycles Asked by jm666 on August 13, 2021
I have a cheap 20" folding bicycle. Its specs say that the max rider weight is 105kg. The frame is steel (vaguely defined as "HiTen" steel).
I want to convert it to electric, so will be adding approximately 12kg more (mid motor, battery, etc.). I also want to carry panniers, let’s say another 20 more kg. My weight is 100kg. So with some reserve, the bike needs to carry approximately 150kg of weight.
I assume that the weak point will not be the steel frame itself, but some components, like bearings, rim material, spokes and so on…
The question is: what components are recommended to change (in general) to get a more sturdy folding bike – i.e. which components have the greatest impact on the load capacity of the bicycle?
I assume that the exact type of bicycle is irrelevant, but let’s say something like this.
Just found this article about the stress analysis of the folding frames. Really interesting reading. https://www.irjet.net/archives/V6/i10/IRJET-V6I10207.pdf
tl;dr: if you want a sturdy folding ebike, you need to have a sturdy folding bike.
Even if the bicycle statically/dinamically can stand more than the declared weight (at your own risk), the (expected) tolerance on the various parts and the quality of all the parts (both in terms of absolute quality and relative quality, relative to quality control) will result in a continuous failure of parts, such as:
Cheap, reliable, light, worry-free. Pick two, if you want a motor: pick one.
Correct answer by EarlGrey on August 13, 2021
On a non-folding bike, I'd look at the wheels, and probably replace them with 36 spoke touring wheels and reasonably wide, tough tyres (e.g. 35mm). The tyres absorb some of the shock loads.
However a folding bike has made some compromises affecting the structural strength, as well as introducing weak points. Two major ones are the main hinge and seat post. The latter is probably OK as your added load isn't on it, but the main hinge will be under added stress from the extra unsprung mass. It's probably not replaceable or serviceable, and obviously overloading the specifications would give the manufacturer an excuse to get out of warranty repair. The risk here is that the frame won't last as long as it should.
Adding a mid drive motor may not be as easy as you think - there's not much room given the need to not affect the folding, combined with the small wheels (short chainstays and reduced ground clearance). A kit for a different folder might help, but might be very specific in its mounting.
Answered by Chris H on August 13, 2021
My main concerns would be spokes in the short term; but wheels can easily be exchanged.
The second and graver concern is the frame. When I was riding about 100km per week, including some cobblestone and curbs, but nothing crazy, even "normal frames" (on your your standard average 500-1000$ bike) started to break; my weight then was around 80kg. (Anecdote: When I started to absorb the impact from going down a curb partly through the handlebar, instead of just through the legs, at some point the handlebar broke!) I never had such trouble when I was lighter; 80 kg seems to be some kind of threshold. I would be concerned about the longevity of my folding bike if I rode it a lot (e.g. an hour each day) with a body weight of 100 kg, no matter what the manual says — without any extras.
That said, you can mitigate the impact of the additional weight by putting the batteries directly over the back wheel, e.g. by putting them on or under a bike rack like in this image. That will not increase the load on your frame much, and neither will your banisters.
Answered by Peter - Reinstate Monica on August 13, 2021
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