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Changing your Rake & Trail on your Bagger



Rake & Trail Our Solution



e know you were day dreaming about sex when the triangles were floating about the blackboard, or for those of you who were already warped, you were doodling motorcycles while the teacher droned on about sins, cosines, tangents. Now all these years later when you finally got the money to build your dream bike, all you can do is thumb through pictures of other people's projects, searching for that "look" blissfully unaware of what all that trigonometry was for. We're going to show you how to do the calculations. We're going to present some data for you to study, and leave the decisions up to you. It might explain why shopping carts weren't meant to go 200 mph. You may download a copy of your very own Rake & Trail Calculator on the page titled: "Rake & Trail Calculator". Play with it (put in all range of numbers from realistic to the absurd),this is how you will learn & understand. It may not help getting you laid at the bar, but it will impress your friends way more than eating a live frog.

Your front suspension geometry is defined by the following six variables which are defined as:



OFFSET:
Centerline of the top steering neck (Stem) to the centerline of the top of the fork tubes.



RAKE Of The STEERING HEAD:
The angle in degrees of the steering neck (head) from the vertical cord (measured in degrees from a line 90 degrees to the ground). Rake is the angle of the forks off vertical and trail is the amount that the front wheel is being pulled down the road, yes, the front wheel is being PULLED not pushed. A good example of trail is the wheels on a shopping cart. The wheel axle is behind the pivot point. This causes the wheel to follow the pivot point no matter where it is going. If the wheel axle were directly under the pivot, you would not be able to keep in a straight line.


TRAIL:
The distance defined by the vertical line (distance between an imaginary line drawn through) centerline of the axle and the steering head/neck to ground intersection.

Trail is what gives us our handling characteristics of our motorcycle. The more trail we have the better our bike handles in a straight line at the cost of low speed turning ability. The less trail we have gives us very responsive low speed handling at the penalty of twitchy higher speed response. Let us think about different ways to change rake and trail. Most Harley® riders make changes in their bikes rake without realizing it. One of the most common modifications to our bikes is to lower the rear end. As the rear of the bike goes down the steering head angle steepens increasing the rake and trail. A change in wheel overall diameter: from a 16” stock FL to a 18” tire will increase the steering head angle thus increasing the rake and trail. The same for decreased wheel diameter from 21 to a 19 will lower the front axle, lessening the steering head angle reducing rake and trail. Increasing fork tube length will increase rake and trail, but a front end lowering kit by itself will decrease it. Stock HD® front ends come with various rakes from 26 to 33 degrees. A good handling bike for highway use will have 2 to 4 inch trail.

FORK LENGTH:
The distance between the top of the fork tubes to the centerline of the axle.

DIAMETER:
The diameter of the front tire. If you do not know, go to my Metzler Tire Guide (link)

RAKED TRIPLE TREES:
In order to bring trail figures back into line, triple trees with raked steering stems can be used. Usually adjustable in 3, 5, 7 degrees of rake.




HOW TO MEASURE CORRECT TRAIL ON YOUR OWN BIKE:
Raise the bike to an upright position, using a tape measure, hold the tape straight down from the front axle to the floor. Put a mark on the floor at that point. Then place the tape parallel to the steering neck, following the angle of the steering neck all the way up to the floor. Put a mark here also. Now measure the distance between the two marks and you have your trail measurement. It should read between 2 and 4 inches. Note: If your bike is equipped with a rear suspension, have someone sit on the seat when you make the measurements to simulate your actual riding condition.



TOO LITTLE OR NEGATIVE TRAIL:
With too little or negative trail (steering axle mark behind the front axle mark), the bike will handle with unbelievable ease at low speeds, but will be completely out of balance at high speed. It will easily develop a fatal high-speed wobble. EXTREMELY DANGEROUS!

NORMAL TRAIL:
Normal trail is somewhere between 2 and 4 inches. The bike will handle easily at both high and low speeds. Flowing smoothly through curves without swaying or wobbling. If you use a very fat rear tire, you should keep the trail as close to 4 inches as possible.



An Example of what Harley Could Do if it wanted: 2001 T-Sport
• Rake/Trail: 28 degrees / 4.1 in.
• Front brake: 2, four-piston dual-action calipers, 12-in. discs
• Rear brake: Four-piston, dual-action caliper, 12-in. disc
• wheelbase: 63.1 in.
• Front suspension: Cartridge-type, 39mm stanchions, 6.1 in. travel, adjustable for spring preload, compression, and rebound damping
• Rear suspension: 2 dampers, 4.3 in. travel, adjustable for preload and rebound



TOO MUCH TRAIL:
If the trail is more than 4 inches, the bike will handle sluggishly at high speeds. It will seem almost too steady. You will have trouble balancing the bike at lower speeds or on winding roads. It will feel generally sluggish and clumsy in comparison to a sport bike designed for accelerated cornering.

ALL TOURING 1980 ~ CURRENT
• Rake / Trail: 26 degrees / 6.2" ~ 6.9" (depending on year and model).
• Front Brake: 2, 4-piston fixed, 11.81" x 0.20" disk (larger disk for the 2008 models)
• Rear Brake : 1, 4-piston fixed, 11.81" x 0.20" disk (larger disk for the 2008 models)
• Wheelbase : 63.5"
• Rear Suspension: 2 dampers, air-adjustably (the absolute worst and cheapest way to raise {adjust} the shock)




STOCK LATE MODEL FL (BAGGERS):
This is how the Factory achieves its steering of steering stem in front of the forks.
The front wheel pushes on the two forks through friction of the road & tire. The forks, because they are behind the steering stem of the wheel is always pushed to self-center.
If the bike is used for putting on long highway miles, than this design is more desirable as you have to drive with far less input (increased trail due in part to the increased fork
rake), the bike is more stable & provides less input going in a straight line.



MOTORCYCLE METAL'S SOLUTION:
26 degrees of rake, 4" of trail. Put some steering performance on your bagger. Big motor?
In an application with steering stem behind the forks lets the forks turn easy as the force is pushing against the steering stem.  Have you ever seen a race bike with a steering stem that is not in front of of the forks?  No!  The disadvantage is having a bike that you must pay attention to driving as in a Dyna or Sportster with a shortened trail (5.1").  Race bikes are around 3"~3.5" of trail.  Have you ever seen anyone running a Sports type racing bike on any Iron Butt (1,000 mi or more) event.  No, because that bike is made for a different purpose.



What it looks like with 13" Penske shocks