In the previous session I started by giving you all an example of what trail is and why it is important to how your bicycle handles. Today, I’m really going to give you a brain teaser!

Remember that trail, in the positive sense as it applies to cycling, has the effect of centering your front wheel when moving forward so that it stays in line with your rear wheel. It’s called a single track vehicle, by the way. How cool is that?! Your tires contact patch with the ground is slightly behind the point where the steering axis would intersect with the ground. Now let’s talk about offset.

Offset is the term used to describe the measurement from the point where your front axle is back to the imaginary line that describes the steering axis. Zero offset would be an axle inline with the steering axis. Offset can be achieved by raking out the fork, running the fork blades slightly forwards of the steering axis by using an offset crown, offsetting the axle by using forward reaching dropouts, and any other means that puts the axle slightly ahead of the steering axis.

What effect does offset have on trail on a typical mountain bike? Well, get ready! Here comes the weird part! Offsetting the hub forward reduces trail. Offsetting the hub more rearward- towards the steering axis- increases trail. Add in the head angle now. Steeper head angle, on its own, will lessen trail, while slacker angles increase trail.

The effects of more or less trail can be looked at in two ways. The higher the trail figure becomes, the more stable and less “quick” in the handling department. The lower trail figures usually lead to a nervous handling and less stable machine. Remember that small changes feel big while riding the bike. A small change of just half an inch either way can result in two completely different handling bicycles. Usually a competent rider can feel even smaller changes in the trail figure. One other effect that trail has is to give a custom builder a way to create more clearance between the foot and front wheel. This is also referred to as toe overlap, a common problem on bicycles of smaller sizes. For instance, smaller sizes of 29”ers suffer from this as the fork offset for front suspension is locked in at a “26”er standard” of 38mm.

Now you can play with these numbers and come up with various combinations that may, or may not work so well. Want to give it a whirl? Then check this out, but only if you are a true geek. http://www.kreuzotter.de/english/elenk.htm This is a fork geometry calculator that is fun to play around with and can even help you understand today’s lesson even better. Class dismissed!