Rake and Trail Basics

The use of a motorcycle must be considered when choosing the rake. With a city with narrow, winding streets (such as Boston or London), a shallow rake would be a disadvantage because the slower speeds would make turning difficult. With an area with open roads and gentle curves (such as my home in Colorado), a steep rake might make the bike skittish and even lead to tank-slappers. The riding situation should guide the angle of rake. Do you need maneuverability at slow speeds, or stability at high speeds, or something in-between?

When motorcycles and bicycles are moving at relatively slow speeds, you turn the handlebars left to go left. When the speed increases, the steering becomes counter-steering, meaning as you turn the handlebars to the left, the motorcycle turns to the right. The motorcycle leans into the turn but the centrifugal effect pushes it back up and the rider tries to balance between the centrifugal effect and gravity. If you don't believe it, watch how you steer into turns the next time you ride. Most riders never notice because that's the way it's always been and feels natural.

The geometry of the steering determines how the bike will respond to varying conditions. Rake is the angle of the steering axis, which is the centerline of the main bearings where the triple-clamps rotate. If you could run a line right thru the bearings and all the way to the ground, the line would show the angle of the rake. The diagram at left shows how the rake is measured, typically is degrees.

The diagram also shows trail, which is typically shown in inches (or millimeters). How trail works is explained below.

At left is a drawing showing how trail can be set independently of rake. The rake is 30 degrees in all three views but the amount of trail is different in each. If you want a fixed angle for steering, the trail can be set to suit your steering needs.

Think of a shopping cart wheel. When you turn the cart, the wheels turn to follow, which is called castor, hence the name "castor wheel." Trail is the same thing, as if the wheel were "trailing" to follow. Trail makes the front steering work, but the distance of trail, shown at right, is a very small amount. Too little and the bike might have light, skittish steering. Too much and the bike won't want to turn at all.

My former chopper is shown at the right. The extended forks and the 45-degree rake might look extreme, if not outright dangerous, but trust me, the bike was a joy to ride. It felt like it was flying on curvy mountain roads. However, the long forks flexed instead of compressing and chattered during braking, but with the right amount of caster I could ride hands-off and the bike remained stable. Yes, the steering was heavy at slow speeds, and yes, the wheel had a tendency to tip at a stop, but above 15 mph, it was little different than any other bike. Click on the picture to see a larger version of the CB750 Frankenbike.

Technical Research: Rake & Trail Basics