3 ms·

This is cool. Except it's driving me nuts that I can't figure out what's wrong with the first picture, or at least why it would immediately break.

my_username_is_ 7y ago
It's missing the chain stays (a section of the frame linking the frame near the rear wheel to the pedal area). There would be a large cantilever arm trying to support a large part of the rider's weight, and it would likely break under the stress.
mayoff 7y ago
It's missing the chainstays, which are the tubes from the bottom bracket (where the pedals attach) to the rear axle. The seatstays (the tubes from under the seat to the rear axle) are only connected to the seat tube with a small weld. When you pedal, you're using the top part of the chain to pull the rear axle toward the pedals. This force is going to break the weld connecting the seatstays to the seat tube. Note that a chain can't push, only pull, so the bottom part of the chain cannot counterbalance this force.
- bjackman 7y ago
  I think the fact that the crossbar is not connected directly to the headtube (part where the fork & handlebar assemblies pivot) would also cause a problem!
tbirrell 7y ago
Its missing the bar from the pedals to the back tire. If you sat on this bike, all your weight would rest on the joint under the seat, bending the front half of the frame away from the back tire, at least sending the pedals into the ground, if not snapping the frame outright.
phiiiillll 7y ago
Picture the downward force generated by sitting on the bicycle causing the rear axle and bottom bracket to spread away from each other, causing the seatstays to break at the seat tube. This is what chainstays prevent on a complete frame.
- Johnny555 7y ago
  Since there's no derailleur, the chain would do a good job of resisting that force (though since it's only on one side, maybe it wouldn't be enough, and the wheel/seat stays would twist) Though when you start to pedal, the chain would tend to pull in and bend the seatstays, but there should be some level of force that is less than the opposite force caused by the rider's weight, so this bike could work under light pedal pressure.
megablast 7y ago
It is missing the part of the frame from the rear wheel to the bottom bracket.
dmurray 7y ago
The back fork should be connected to the seatpost with a pair of horizontal braces. It's an exaggeration to say it would immediately break. But if you put weight on it, it will tend to spread out (imagine putting weight on a bent piece of metal shaped like a ^). Still, the front fork isn't braced, and bikes exist with quite a large rake angle on the front fork (think a Harley-Davidson style chopper). So maybe you can make this design strong enough to bear a person's weight.
- dTal 7y ago
  As it's a single speed with no derailleur and the missing braces would be in tension, might not the chain itself fulfill the role?
  - bsmith 7y ago
    It could, but undue tension on the chain vastly decreases the efficiency and longevity of the chain, and potentially, the cog/chainwheel. This would also present a safety issue because chains can (and do) break.
deleted 7y ago
[deleted]
gilbetron 7y ago
Other people pointed out the chainstays are missing, although most people are missing out why they are important. Hint: the name tells it all! Without them, the back "triangle" of the bike would flex, causing the distance where the chainstay would be to shorten, resulting in the chain popping off the gears, or at least causing it to skip a bunch. The chainstay causes the chain to ... stay.
zild3d 7y ago
in addition to what others mentioned, the chain attached to both wheels will make turning.. difficult

my_username_is_ 7y ago

It's missing the chain stays (a section of the frame linking the frame near the rear wheel to the pedal area). There would be a large cantilever arm trying to support a large part of the rider's weight, and it would likely break under the stress.

mayoff 7y ago

It's missing the chainstays, which are the tubes from the bottom bracket (where the pedals attach) to the rear axle. The seatstays (the tubes from under the seat to the rear axle) are only connected to the seat tube with a small weld. When you pedal, you're using the top part of the chain to pull the rear axle toward the pedals. This force is going to break the weld connecting the seatstays to the seat tube. Note that a chain can't push, only pull, so the bottom part of the chain cannot counterbalance this force.

bjackman 7y ago
I think the fact that the crossbar is not connected directly to the headtube (part where the fork & handlebar assemblies pivot) would also cause a problem!

tbirrell 7y ago

Its missing the bar from the pedals to the back tire. If you sat on this bike, all your weight would rest on the joint under the seat, bending the front half of the frame away from the back tire, at least sending the pedals into the ground, if not snapping the frame outright.

phiiiillll 7y ago

Picture the downward force generated by sitting on the bicycle causing the rear axle and bottom bracket to spread away from each other, causing the seatstays to break at the seat tube. This is what chainstays prevent on a complete frame.

Johnny555 7y ago
Since there's no derailleur, the chain would do a good job of resisting that force (though since it's only on one side, maybe it wouldn't be enough, and the wheel/seat stays would twist) Though when you start to pedal, the chain would tend to pull in and bend the seatstays, but there should be some level of force that is less than the opposite force caused by the rider's weight, so this bike could work under light pedal pressure.

megablast 7y ago

It is missing the part of the frame from the rear wheel to the bottom bracket.

dmurray 7y ago

The back fork should be connected to the seatpost with a pair of horizontal braces. It's an exaggeration to say it would immediately break. But if you put weight on it, it will tend to spread out (imagine putting weight on a bent piece of metal shaped like a ^). Still, the front fork isn't braced, and bikes exist with quite a large rake angle on the front fork (think a Harley-Davidson style chopper). So maybe you can make this design strong enough to bear a person's weight.

dTal 7y ago
As it's a single speed with no derailleur and the missing braces would be in tension, might not the chain itself fulfill the role?
- bsmith 7y ago
  It could, but undue tension on the chain vastly decreases the efficiency and longevity of the chain, and potentially, the cog/chainwheel. This would also present a safety issue because chains can (and do) break.

deleted 7y ago

[deleted]

gilbetron 7y ago

Other people pointed out the chainstays are missing, although most people are missing out why they are important. Hint: the name tells it all! Without them, the back "triangle" of the bike would flex, causing the distance where the chainstay would be to shorten, resulting in the chain popping off the gears, or at least causing it to skip a bunch. The chainstay causes the chain to ... stay.

zild3d 7y ago

in addition to what others mentioned, the chain attached to both wheels will make turning.. difficult