What is Rake and Trail...
I was sitting here eating a piece of pizza when I suddenly had an urge to share some information... I have had several people ask me about Rake and Trail so I thought I would try to explain just what they are and how they relate to our sport.
Rake is the angle of the forks off vertical and trail is the amount that the front wheel is being pulled down the track, Yes. the front wheel is being PULLED not pushed down the track. A good example of trail is the wheels on a shopping cart.
Above you will notice the wheel axle is behind the pivot point. This causes the wheel to follow the pivot point no matter where it's going. If the wheel axle was directly under the pivot you wouldn't be able to keep the cart in a straight line and shopping would become an extreme sport.
The more trail you have the greater the high speed stability, the trade off is that the steering gets heavy and slow at low speeds. One of the reasons we need more trail is the bumps in the lights caused by our 4 wheeled friends jamming on the brakes so they don't break out. This actually pushes the pavement ahead causing waves. By increasing the trail we are able to ride through these bumps at over 200 mph without going into tank slappers.
The way to measure the trail is to draw a line through the steering head to the ground.
Like the red line, then draw a vertical line through the front axle to the ground like the green line. Measure the distance between these two lines and that is trail.
There are several ways to increase trail. One is to "SHORTEN" the offset on your triple trees.
If you increase the offset you will get "LESS" trail, this is not a good thing for Drag Racing.
The other (and preferred) way is to rake the frame.
Notice the increased distance in the trail measurement. This involves cutting off the old steering head and replacing it with a new one at an increased angle. Do yourself a favor and have someone who knows what they are doing tackle this job, your life may depend on it.
Here's a little something to think about, When you apply the brakes say in the lights and the front end dives down, "YOU ARE LOSING TRAIL," If you are running marginal trail to begin with you could be in trouble when you go to stop.
One last thing......I have heard a lot of discussion about raked triple trees...
This is "A BAD IDEA" for a drag bike. As you can see in the drawing, you could end up with little or no trial. The road race guys use this method to make their bikes turn better on the slow part of the track and it's only 1/2 to maybe 1 degree change. If you have ever seen a Road Race bike at speed you will notice they are on the verge of crashing the whole way down the straight-away.
It's OK to change your bike to make it work better for what your doing just be careful and think it out before you attack your chassis with a torch.......