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When you read such post as this one https://bikeinsights.com/cyclopedia/trail you will learn how offset and head tube angle affects steering.

But I wonder about those parameters in "reverse" -- given trail (constant) when we change offset and angle what is the difference in steering?

For example: 760 mm wheels, one bike A with angle 78 degrees and offset 0 mm gives 80.8 trail, while another one B with angle 69 degrees and 61 offset gives 80.5 mm trail, so pretty close (let's call them even).

The difference of course is in the flop, for A it is 16.4mm, for B 26.9mm.

What would be the difference in actual steering? I am especially interested in such factor as self-correcting.

Equations: https://en.wikipedia.org/wiki/Bicycle_and_motorcycle_geometry#Wheel_flop

greenoldman
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  • What’s the context here? Technical trails with a suspension rock? Road racing? – Paul H Jan 13 '23 at 05:09
  • And what is the definition of flop? – ojs Jan 13 '23 at 11:11
  • It's even more complex than that. Where the weight ends up can change a bike's self correction / flop / handling even more than a change in HTA, rake. (This is particularly noticeable in recumbent bikes, where moving a rider forward or backward an inch can change handling characteristics.) The good news is that riders can get used to just about anything in the realm of "normal" very quickly. –  Jan 13 '23 at 13:05
  • @PaulH, Rigid fork, since suspension would add additional factor of sagging. Context is riding straight, I am not asking about particular race/event/trip but the nature of the bike. I selected those parameters to have constant trail so the variables would be only offset and angle (and as a derivative -- flop). – greenoldman Jan 13 '23 at 14:36
  • I'll say this, as mountain bikes have gotten longer and slacker, they are increasingly spec'd with low offset forks. Those forks seems to provide a very acceptable balance of high-speed stability and low-speed maneuverability. IME, a modern bike with a 160 mm fork and a 64º HTA navigates tight switchbacks better than the 120 mm, 70º HTA bikes of ten years ago. – Paul H Jan 13 '23 at 15:28
  • @PaulH,I am lost how it is relevant to my question. Comparing bikes with different trails is out of scope this post. – greenoldman Jan 13 '23 at 17:53
  • Your question loosely boils down to: "how do HTA and fork offset affect steering. My comment (not an answer) boils down to: "when MTB designers slackened head angles, they seem to have been able to undo some of the negative effects (slow steering) by reducing fork offset." So one might conclude that lowering the offset makes the steering more responsive. – Paul H Jan 13 '23 at 18:23
  • @PaulH, no, if it it was my concern I would asked the question the way you presented. But I didn't, keeping the trail constant is crucial for this question. If you don't comprehend this, I am sorry, but those comments do not add anything, except creating only noise. – greenoldman Jan 14 '23 at 04:36

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As I always understood it, trail is the tendency of a bicycle to straighten itself out (to self-steer the front wheel to counteract a course deviation), and flop is a measurement of "turn-in," that is, the ease with which it can be steered off-course. But this article goes into a lot of detail explaining that A) flop is often defined incorrectly, and B) we don't have a good grasp of what (if anything) flop represents even when defined correctly.

I am reminded that bike stability has been studied in an academic setting for decades, and still isn't fully understood.

Adam Rice
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