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I'm building my first bike: probably steel (easy to work with). 2X26" road tires. Full suspension. Will be used on sandy dirt roads, and paved streets with moderate incline. Want hands free option, and good directional stability--both seated and standing on uphill sections.

Which design factors will help stability? How much trail, fork shape, crank more forward or backward? What else?

closed as too broad by Batman, mattnz, andy256, Móż, jimchristie Nov 2 '16 at 20:07

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    You may find this question about bike design helpful, and there are more answers in this question about bicycle stability Simply put, your question is very broad. – Móż Nov 2 '16 at 2:33
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    Pretty much everything on a bike affects stability, even if a little. – Batman Nov 2 '16 at 2:50
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    Er, welcome to Bicycles @George. Good to see you've taken the tour! Your first question is certainly generating some interest, with some people wanting to close it as too broad. Móż has at least given an answer, which has triggered some cynical replies. I'm a bit confused about a few of things: a) for a first bike, why are you not copying an existing bike? b) why complicate your first bike with suspension? c) why suspension at all? d) why suspension when the intended use is roads? (you can see I'm not a fan of suspension). ... – andy256 Nov 2 '16 at 5:32
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    ... Whole books are written about bicycle design. and PhD's also. There's a huge amount on the web about it. On the one hand, it's complicated. One the other hand, the basic design is very stable and simple. Have fun. (BTW, Móż speaks from his experience of building various bikes). – andy256 Nov 2 '16 at 5:35
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I'm just going to make a list of all the factors I can think of that affect stability, but please be aware that this list is not exhaustive.

  1. front tyre size/width
  2. front tyre weight
  3. front tyre pressure
  4. front wheel size
  5. front wheel rigidity
  6. headset angle
  7. trail
  8. front fork rigidity
  9. front fork travel
  10. front fork suspension friction
  11. front suspension travel shape
  12. front fork preload
  13. stem length / handgrip position relative to steering pivot
  14. handlebar rigity
  15. grip size and firmness
  16. primary frame/main triangle rigidity
  17. main triangle size and angles (affects BB to handlebar and seat position)
  18. rear triangle rigidity
  19. rear suspension type
  20. rear suspension travel
  21. rear suspension travel shape
  22. rear suspension preload
  23. slop in suspension pivots (all six axes)
  24. slip in all the other bearings - headset, bottom bracket, wheel axles etc
  25. BB to ground distance
  26. seat height
  27. seat front-back position
  28. seat firmness
  29. Q factor (BB/crank/pedal spacing)
  30. chainstay length
  31. rear wheel size
  32. rear wheel rigidity
  33. rear tyre size/width
  34. rear tyre weight
  35. rear tyre pressure

I am certain that I have missed some, and a few of the entries above should really be split out a great deal more - the rear triangle could be made of composite materials allowing fine, semi-independent control over rigidity in different axes, for example. And vertical compliance of the main triangle is a subject of intense discussion in some cycling circles. Likewise, suspension design is a complex subject that's quite different from suspension tuning, but I've largely conflated them in the list above.

  • You forgot the water bottle cage(s), location, with or without bottles, full or empty or somewhere between, shape of bottle (sloshiness) and whether its plain water or has something in it. – Criggie Nov 2 '16 at 4:44
  • Wear on all of those components too - new is not the same as part worn. – Criggie Nov 2 '16 at 4:45
  • Tire content - whether it has air, slime, tubes or tubeless, how much mud, and where patches might be located on the tube. Presta or Schrader valves? Is the tyre sidewall label in line with the valve? – Criggie Nov 2 '16 at 4:46
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    Rider mass, rider frontal area and shape, re-entry angle and velocity, atmospheric density, phase of the moon, ... – andy256 Nov 2 '16 at 5:21
  • I think that this should be up voted once for every point listed. Keep going @Móż! – andy256 Nov 2 '16 at 5:36

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