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Rake and Trail 101 – Page 1

Rake and Trail 101 – Page 1.

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Rake and Trail 101 – Page 1

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  1. Rake and Trail 101 – Page 1 Let us use this simple castor wheel to define Trail. The Trail is shown below as the distance between the ground contact point of the tire and the steering axis. Now try to imagine the red horizontal line is attached to the castor wheel and we will use it as a handle bar to steer. The bigger the trail distance, the harder it will be to steer because the caster wheel will have more leverage to try and straighten itself out when turned. Let’s also try to imagine reversing the direction of travel. This would be a case of negative trail. Now try to imagine holding the handle bars. You couldn’t let go even for an instant if you could hold it at all. The instant you let go, the wheel would swing around the other direction, just like a shopping cart wheel going backwards. In the case of the caster wheel as shown, the rake is 0, the steering axis is vertical. Steering Axis Handle Bar Direction of Travel Ground Line Tire Contact Point Trail

  2. Rake and Trail 101 – Page 2 Now lets add some rake angle. Not Much has changed really. The trail is now defined as the distance between the tire contact point and the intersection of the ground and the steering axis. Steering Axis Handle Bar Direction of Travel Point at Which the Steering Axis Intersects the Ground Ground Line Trail Tire Contact Point

  3. Rake and Trail 101 – Page 3 Now let’s look at a raked triple tree. The Front wheel is pushed forward without changing the steering axis of the frame. The trail is reduced. This is OK up to a limit. We wouldn’t want negative trail numbers, that would be extremely unsafe, and trail numbers that are too small are also unsafe. Now let’s look at a basic motorcycle setup with stock triple trees. The trail in this case will be somewhere between 4-6 inches. This is considered the safe zone. Steering Axis Direction of Travel Steering Axis Rake Angle Rake Angle Point at Which the Steering Axis Intersects the Ground Ground Line Reduced Trail Trail Tire Contact Point Tire Contact Point

  4. Now that we have the concept, lets look at the VTX1800 as an example. The stock Rake is 32 degrees. There is 0 additional rake angle in the triple trees. The stock trail is around 5.8 inches. That’s a good solid number for a big cruiser. Rake and Trail 101 – Page 4 Lets take a quick look at some 6 degree triple trees. There are other factors that determine trail, such as tree offset, and especially wheel diameter. In the case however of the 18 inch stock front wheel on a VTX 1800, if the 6 degree tree has a similar offset to stock tree at the top, the trail will be somewhere around 2 inches. This is OUTSIDE the safe zone. This is Why Kewlmetal does not recommend 6 degree trees for stock frames. This is also Why Kewlmetal makes a 3 degree tree. A 21 inch front wheel will increase the trail almost 1 inch on this setup, giving about 3 inches of trail. Still low, but better. An 8 degree triple tree on an otherwise stock VTX has almost 0 trail, while this setup works on a Trike, it is absolutely dangerous on a motrocycle. So in conclusion, if you want to rake your VTX 1800 past 38 degrees (32 stock + 6 trees), you will need to modify the steering head in some manner to increase the trail with the increased fork rake (front wheel pushed WAY forward). Basically there are 2 ways to do this, cut and weld your frame, or the Kewlmetal bolt on KMPS kit. Steering Axis Rake Angle = 32 degrees Point at Which the Steering Axis Intersects the Ground Ground Line Trail = 5.8 Inches Tire Contact Point

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