5 ms·

Just to expand on what others said, the tubes that the frame is missing are called chainstays.

qznc 11y ago
Is it really impossible to build such a bike? Given a strong enough material it would be possible. I have not idea about the structural analysis in this case. Does such a material exist?
- arethuza 11y ago
  I can't see what the advantage would be though - if you do have a wonder material better to go with a more standard frame design and increase stiffness and/or reduce weight. NB ~20 years ago I did have an "elevated stay" frame which was neat in some ways - no chain slap and the chain didn't go through the frame. However, the frame failed catastrophically while I was at traffic lights....
- Piskvorrr 11y ago
  "I have not idea about the structural analysis in this case." There's your problem. The chainstays are there for Good Reasons. http://www.mece.ualberta.ca/tutorials/ansys/BT/Bike/Bike.html http://www.mece.ualberta.ca/tutorials/ansys/BT/Bike/Bike.htm... If you take them out, now most forces on the bike effect one point in the frame, right beneath the saddle. Making the frame stronger requires more material (=weight) or better material (=price), whereas a rhombus of two triangles solves the problem efficiently. In other words, you are proposing a problem to which the current bike design is the solution.
- provemewrong 11y ago
  Likely not impossible, but the crucial weak point would probably be the connection with the seat tube. Independent of the material, that place would need some heavy gusseting/reinforcement. That particular bike also has a very vulnerable connection to the head tube, as only the down tube connects to it. There are bikes without a rear triangle, but they (almost?) always lack the seatstay instead of the chainstay or have what could be considered something in between a chainstay/seatstay. Here are some examples: http://i.imgur.com/F1xkdc1.jpg http://i.imgur.com/F1xkdc1.jpg http://i.imgur.com/oTFbEy7.jpg http://i.imgur.com/oTFbEy7.jpg http://i.imgur.com/XxRNe5y.jpg http://i.imgur.com/XxRNe5y.jpg
- maxerickson 11y ago
  In practice, bikes that diverge from 2 triangles eschew the support between the rear hub and the seat: https://www.google.com/search?q=carbon+fiber+bike+frame https://www.google.com/search?q=carbon+fiber+bike+frame (the results are mostly traditional, there are some with a different configuration for the frame supporting the rear hub)

qznc 11y ago

Is it really impossible to build such a bike? Given a strong enough material it would be possible. I have not idea about the structural analysis in this case. Does such a material exist?

arethuza 11y ago
I can't see what the advantage would be though - if you do have a wonder material better to go with a more standard frame design and increase stiffness and/or reduce weight. NB ~20 years ago I did have an "elevated stay" frame which was neat in some ways - no chain slap and the chain didn't go through the frame. However, the frame failed catastrophically while I was at traffic lights....
Piskvorrr 11y ago
"I have not idea about the structural analysis in this case." There's your problem. The chainstays are there for Good Reasons. http://www.mece.ualberta.ca/tutorials/ansys/BT/Bike/Bike.html http://www.mece.ualberta.ca/tutorials/ansys/BT/Bike/Bike.htm... If you take them out, now most forces on the bike effect one point in the frame, right beneath the saddle. Making the frame stronger requires more material (=weight) or better material (=price), whereas a rhombus of two triangles solves the problem efficiently. In other words, you are proposing a problem to which the current bike design is the solution.
provemewrong 11y ago
Likely not impossible, but the crucial weak point would probably be the connection with the seat tube. Independent of the material, that place would need some heavy gusseting/reinforcement. That particular bike also has a very vulnerable connection to the head tube, as only the down tube connects to it. There are bikes without a rear triangle, but they (almost?) always lack the seatstay instead of the chainstay or have what could be considered something in between a chainstay/seatstay. Here are some examples: http://i.imgur.com/F1xkdc1.jpg http://i.imgur.com/F1xkdc1.jpg http://i.imgur.com/oTFbEy7.jpg http://i.imgur.com/oTFbEy7.jpg http://i.imgur.com/XxRNe5y.jpg http://i.imgur.com/XxRNe5y.jpg
maxerickson 11y ago
In practice, bikes that diverge from 2 triangles eschew the support between the rear hub and the seat: https://www.google.com/search?q=carbon+fiber+bike+frame https://www.google.com/search?q=carbon+fiber+bike+frame (the results are mostly traditional, there are some with a different configuration for the frame supporting the rear hub)