Rake, trail, and offset are the most vital concepts relating to the feeling of any motocross machine on the track. The handling of a motocross machine is made complex by all the weight distribution and geometry involved. Even if a rider is great at feeling his way around a dirt bike, this can get confusing, simply due to how complex the action and reaction of each geometry change. The foundation of the handling of a bike is in its design, which comprises of the rake, trail, and offset. I have been speaking with smarter people than me when I have been testing lately so that means I have been asking a lot of questions. When I give feedback to the engineer about a certain feeling that I am getting, I like to understand why I could be feeling the bike do certain (different) things with certain chassis change points. I have been testing offset clamps, races, fork heights, wheelbases and linkages for years, but wanted some of you out there to understand what rake, trail and offset really mean to your bike at home.
Rake:
The rake of a motorcycle is sometimes termed as the “fork angle”. This name is not accurate, however, as the rake is a variable calculated to the steering head and not the fork or fork legs. The rake as a number represents the angle between two imaginary lines. The first line is vertical and it runs to the riding surface, passing via the center of the bike’s front wheel. The second line passes through the steering hub’s center and is among the characteristics of the frame, and not the fork. The angle between the two lines is referred to as the rake or rake angle.
It plays a crucial part in the handling characteristics of a bike and it is usually regarded that the responsiveness of a bike’s handling is inversely reacting to the rake angle values. The smaller the rake angle, therefore, the more agile a bike could be. Some manufacturers have fixed values for specific line-ups, such that the bikes have consistent handling feeling through model years. Basically put, the rake can decide on how fast a bike will respond to the movement of its front wheel. A small rake represents an immediate reaction. Some riders will describe a smaller rake angle as having the front wheel “nearer”closer to them when seated.
Trail:
Visualizing the trail concept is a little more tricky. It is expressed as a numeric variable that represents a measure of length in centimeters or inches. The trail is inherently connected to the rake and it plays an equally crucial part in the stability and handling of a bike. A motorcycle’s trail is described as the distance calculated from the center of the contact patch of the center to the mark where an imaginary line crossing via the center of the headstock axis intersects with the ground. Offset is actually an engineering solution to influence the relationship between the two concepts.
A trail can be thought of as a buffer zone in relation to the movements of the handlebars. In motocross bikes with bigger trail values, the steering wheel function almost acts like a caster and the longer the supporting arm, the stronger the wheel’s force when it is attempting to realign with the direction of travel.The steering effort that is needed to maintain the wheel in the new direction will also be much higher. Bigger trail values represent stability. However, the extra trail takes handling back onto the less stable area. Bike manufacturers and engineers are continually trying to always narrow down a combination for a specific purpose for the consumer. Trail and rake are not sufficient to determine the optimal stability of a bike. Other concepts come into play, including the suspension settings, the type of suspension, as well as the load of the motorcycle.
Offset:
The offset is also calculated between two imaginary lines, like trail and rake. It denotes the distance between the axis crossing via the steering center and the axis crossing through the steering stem center. The offset of a bike is controlled with several shapes of the triple tree, which is the piece that clamps the form tubes and which binds the front end to the frame. Triple trees are typically constructed from machined or forged aluminum and are among the vital parts of the steering assembly. Offset impacts on the bike’s trail, that is the bigger the offset, the smaller the trail. If a motorcycle has little trail, it is recommendable to reduce the offset and maintain the steering in more manageable limits. The offset can be altered with aftermarket triple trees, which have yokes that are manufactured differently from the stock OEM kinds, although the same result can be gotten with varying steering head axles. Offset is mainly used as the primary component for adding maneuverability to custom motorcycles.
Extremely long forks can have an adverse impact on a bike’s handling, and designers utilize special trees to rectify the figures while preserving the aesthetics of their designs. The offset can be thought of as a “tool” for impacting the trail while leaving the rake intact. If you determine that your motorcycle requires adjustments, your best bet would be to involve a specialist. They will be more empowered to do appropriate calculations and identify the trail and rake values that will ensure the stability of your machine. In extreme cases, you can end up with a negative trail which translates to significant efforts in maintaining directional control.
The Relationship Between The Three Concepts:
If the value of the rake increases, the trail increases
If the value of the trail increases, the rake increases
If the offset for the triple clamps increases, the trail decreases
Head Angles:
Motocross bikes have head angles in the range of 62.5- to 64-degrees. Steeper head angles turn better and can work better on a tighter track. The longer the head angle, the more the front wheel will resist turning, the larger the turning arc will be (or what we know as pushing in corners) and the better it will be in a straight line.
Wheelbase:
Wheelbase is the distance between the front and rear axles. A longer wheelbase turns slower, tracks smoother over rough terrain and is less affected by rider position. Shorter wheelbases are more responsive to weight shifts, turn quickly and ride roughly. The measurements from swingarm pivot to center of axle for most motocross machines typically fall into the 595mm to 615mm range.
How Can You Make Your Bike Handle Different?
The weight bias and head angle can be influenced through preload adjustment, suspension settings, bar position and by sliding the forks up and down in the triple clamps. If you raise the bike in the back and set your bars so you can weight the front, the bike will turn quicker and be less stable on high speed tracks. If it’s taller in the front with a more rearward weight bias, the bike will turn slower and be more stable (AKA, Aaron Plessinger set up). Removing or adding a link in the chain makes it possible to lengthen or shorten the wheelbase. Short wheelbases turn sharper, hook up better out of the corners and feel more nervous on high speed. Longer wheelbases are more stable and usually are more popular with today’s racers.
Aftermarket triple clamps are available in a wide variety of offsets. Depending on the fork offset, aftermarket clamps can speed up or slow down handling. More offset results in quicker steering. Less offset makes the steering heavier but more controlled. Aftermarket linkages can lower the rear of the bike to kick the head angle out. The rider can then raise or lower the forks to choose the head angle that he wants while also lowering the center of gravity Steering head races can offset your bike’s head angle/trail and can help create more stability. Steering head races are usually made typically offset to make a bike more stable in straight line (or have a heavier steering feel).
Feeling On Track:
Why do I feel like the bike is more stable on straight line when I go from a 22mm offset to a 24mm offset if the trail is decreased? This is something I struggle with and from what you just read above, it should be the opposite feeling on the track right? Having more of a tire contact patch feel (decreased trail) can make the rider feel like the bike is more planted (heavier steering feel) to the ground thus giving the “feel”of more stability. I am not a smart enough man to tell you why riders feel this way, if science is telling us another, but when you go from a 22mm offset to a 24mm offset (or even a 20 degree offset steering head race) the feeling on the track is usually a more planted stable feel which can affect cornering because of the heavy lean in nature of the new angle of the machine. Yes, confusing I know, but once I wrapped my head around these concepts above it helped a little when testing. Most of the time I don’t get the luxury of knowing what the team of engineers have done to the bike before I go out and test a change point as this could skew a rider’s view of machine (pre-notion). This is the big difference between media testing and production suitability testing. Blind testing is almost always a better way to get direction for a motorcycle no matter what the numbers say behind it
