Hmm, if you draw a line straight down the steering axis of your bicycle, it seems to me the wheel contacts the ground AHEAD of where the steering axis intersects the ground. Certainly the hub of the wheel is ahead of it, the way the fork bends forward . . . I suppose I should look at my kid’s bike, see where the actual tire touches. Okay, ignore me until I verify this.
That’s right, SoDamnHip, the steering axis trails the axle, making the wheel tend to point straight ahead. More trail, more stability. Less trail, easier low-speed steering. Too much trail,and the bike won’t make quick turns. Too little, and it gets very twitchy.
Welcome to the Straight Dope Message Board, SoDamn.
When you start a new thread, it is helpful to others if you provide a link to the Staff Report that you’re commenting on. In this case, Balancing on a bicycle… helps keep everyone on the same page.
Check out this link: www.paintbros.com . It is about motorcycles but the mechanics are the same. The staff report had positive and negative trail confused. If the steering axis meets the road ahead of the center of the contact patch, that is POSITIVE trail. Positive trail is necessary for easy riding. It’s possible to ride with negative trail but VERY difficult.
On the Harley Davidson website they show specs for each of their bike models and they state the trail, in inches, for each mode. I offer this just to show it is a subject some people are familiar with.
Bindlestiff aka, The Dutchman
Here is one diagram showing trail. The steering axis is more tilted than you might expect, and the axis intersects the ground far ahead of the actual steering bearings (headset). The fork is bent forward (“rake” or “fork offset”) to reduce, but not eliminate, the trail. Too much trail results in a very “heavy” feel.
On some bikes, the steering axis is almost vertical. In extreme cases you need to bend the fork backwards to provide enough trail. The BikeE E2 is one such example.
Please note that there is another (longer) thread on pretty much the same topic: Balancing on bikes
As forum moderator, I’m going to leave this thread opened, because it’s perhaps slightly different, but I’m going to urge that people post in the other thread so that we’ve got one location for all this discussion.