someone somewhere here put up an explanation and diagram explaining tuck under but I can’t find it … can anyone enlighten me on tuck under (and stem length and head angle effect) please

I believe it’s this: The trail shortens as you turn the bars because the longitudinal distance between projected steering axis and contact patch gets shorter. Eventually it becomes a negative distance (contact patch in front of steering axis) at which point the steering tends to jack-knife instead of self-centring.

It always seemed to me that steeper head angles were more prone to tuck under, but it will also be affected by fork offset, rake etc and also your position on the bike and riding style as to whether you really experience it.

Gary Fisher introduced his G2 geometry to keep steering stable but quick, so that might have a little blurb in and amongst it on tuck under?

What chief said