Tuesday, November 29, 2005

Geometry Class: The Long And Winding Trail: Part II

Welcome to an abreviated edition of The Long And Winding Trail. I almost had to take a "snow day" today, as we got our first chilly blast of ice and snow that's going to stick around awhile.

Yesterday 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 mountainbike? 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 it's own, will lessen trail, while slacker angles increase trail

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.

That's it for today! Gotta dig out the studded tire bike for the run in to work today! Class dismissed!

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