Originally Posted by
icemilkcoffee
The one place where a zero length stem would have an issue, is trying to ride with no hands.
One of the self-steering mechanisms on the bicycle, is that when the bike starts falling to one side, the handlebar will also flop to the same side because of the weight of the bar at the end of the stem. This helps arrest the fall. (there are other effects to help self-steering too. Namely gyroscopic precession and tire camber). This effect is especially pronounced at low speed. If the stem is zero length, the weight of the handlebar will not cause the fork to turn, hence less self steering. If the stem is pointing backwards, it's even worse- it's working at cross purpose now.
If you are running a zero length stem, you could attach a lead weight to a stick that attaches to the bars or stem. A front reflector holder for example. This will help replace this self steering effect lost by going to zero length stem.
Ya, notsomuch.
Stem length has little to do with whether a bicycle will self-steer or not. Head angle, fork rake/offset and trail, along with overall wheelbase, determine how stable a bike will be, hands-free.
Stem length does affect a couple of things, though “above the headset,” as it were; firstly, stem length, along with bar width, changes the leverage ratio between the movement of your hands (distance) and the amount of angular deflection of the front wheel. Shorter stems and narrower bars will produce more change in the front wheel angle for a given input at the grips, for more responsive or “twitchy “ steering.
The other thing stem length can affect is how much of the rider’s weight is placed on or ahead of the front wheel. Working in combination with top tube length, moving the rider’s weight forward of the steering axis uses that weight to counter forces from the road conditions (like bumps) from deflecting the front wheel as much. That’s why you see long, low stems on short-wheelbase, fast-steering bikes like Crit bikes and XC racers, to impart some straight line stability, while still being highly responsive when called for.