Rake & Trail

A great discussion on the importance of Trail to Chopper Geometry from Chopper Kit USA.

Elementary Chopper Geometry
Here are some basic chopper geometry facts that I discovered in my quest. Probably the most important aspect when planning a chopper project is the trail dimension. The trail dimension is a large factor in determining the handling characteristics of the bike. A proper trail dimension will insure a proper handling bike with no surprises. A trail dimension that is extreme will make a bike difficult to handle and in some cases down right dangerous.

A stock setup with normal rake and trail dimensions. With the trail dimension somewhere between 2 to 4 inches, the bike will handle easily at both high and low speeds. Flowing smoothly through curves without swaying or wobbling.

The rake angle is increased at the neck. If the trail dimension is too great, the bike will handle sluggishly at high speeds. It will seem almost too steady. You will have trouble balancing your bike at lower speeds, or on winding roads. It will feel generally sluggish and clumsy.

The rake angle is increased at the trees. With too little and in extreme cases negative trail, (steering head angle point falls behind the front axle point), the bike will handle with unbelievable ease at low speeds, but be completely out of balance at high speed. It will easily develop a fatal high-speed wobble. Extremely dangerous!

One of the major reasons that I decided to go with the AME chopper kit is the design of the steering head. AME states that "the bike retains the stock trail dimension" and "is safe and drivable up to the top speed of the bike". The way they do this is to combine both neck and tree rake angles to achieve the overall rake of 14 degrees for the kit. The rake at the neck is approximately 9 degrees and the rake at the trees is approximately 5 degrees, for the 14 degree rake total. The neck rake angle increases the trail dimension and the tree rake angle, in turn, decreases the trail dimension. So, what you end up with is a canceling effect on the trail dimension while the rake angle is increased by 14 degrees. In short, by incorporating both rake methods, the AME chopper kit DOES maintain the stock trail dimension.