Reflections on fat-tire road bike geometry

[Kontact]

Originally Posted by marciero

Yes, trail would be different. The affect I was getting at is separate thing from wheel flop. If you take flop out of the equation there is still a difference in the steering. In the extreme case of HTA =90, the wheel flop is zero. A point on the top of the wheel does not move when you turn the bars. Nor would the frame move if the bike were stationary. If HTA is less than 90 and you adjust the rake to give zero trail the wheel flop is still zero. But now when you turn, a point on the top of the wheel moves in arc. If the bike were stationary, the frame would move, pivoting about that point. I think that this gives rise to subtle but noticeable affect in handling.

Again, all true. While riding yesterday on a bike with a 72.5° HTA, I batted the handlebars back and forth trying to feel wheel flop and the resulting acceleration in the handlebars. I honestly could not sense much of anything, despite the moderately slack angle. I can't imagine feeling even less with a 73.5° HTA.

I just don't think it is going to be nearly as evident as trail or wheelbase, and more like the difference you get in handling from a slightly longer stem. There is definitely going to be a point where the difference in flop is obvious, but even at 70° HTA the wheel flop is only 21% of a 74° HTA. I think the bike would have to practically look like a chopper before it rises to the level of being observable.

[weisan]

Just read through this whole thread again. So much good stuff packed in here. Many thanks to Velo pal for starting it and writing an awesome first post.