Rake and Trial Explained
You’ve probably strolled along hundreds of bikes and noticed that there are a lot of different fork angles. Some have their forks almosty laying flat on the ground while sport bikes have a fork that stands almost verticaly. Some just go for an extreme look while others are seeking for that ultimate performance from their front fork. Does this mean that a bike with a less steap fork angle performes better than a a raked out chopper? And what about springers? It all depends on a few variables, that is off course besides the overal construction of the front fork itself. 🙂
Breaking it down: Rake
The first and most mistaken variable is the Rake. The rake you see is not the rake we mean right here. The rake you see is the rake of the fork in comparrison to the frame/ground, the fork rake. Although this influneces the handling of the bike this is’t the rake you should be looking for on your quest for a good handling bike.
The determining factor here is the rake of the frame relative to the vertical axis as shown in the picture below. By applying force on your handelbars that acts on the fork through the handelbars. Rake comes into play with the angular distribution of the applied force on the handlebar.
The closer the wheel is to center of gravity of the bike the easier it is to turn. So with a small rake angle a bike turns pretty easy. This is perfect when looking for a bike that has a small turning radius since you have a small wheel base. On the other hand the bike can become unstable on higher speeds. The extreme opposite is a large rake angle. This way you increase the wheelbease of the bike but also giving it an almost impossible turning radius and you need to apply way more force to turn the wheel. When it come to stability a raked out bike handles perfect when riding high speeds but is less stable on slower speeds due to the bike’s inability to support itself.
So rake depends on what kind of bike you are looking for and what you are planning to do with is. If you looking for a bike that handles like a dream for riding in the city en never go any faster than 80 km/h than a short wheelbase is what your looking for. Planning a cruising down the higway for hours on one end than a raked out bike aint such a bad idea. The “golden” rake is used on tourers and cruiser for a perfect mix of both worlds, with about 29 and 32 degrees, while some choppers are at the edge with about 45 degrees. Most likely you’ll find the rake angle to be anywhere from 22 to 32 degrees, as those angles are tried and proven in terms of stability, response and looks as well.
Screwing up your rake angle can be disastrous for riding your bike, so it’s mandatory to set it up just right. So look for a rake that suits your riding style, what works for me doesn’t have to work for you.
The big influencer: Trail
So that was part one of the course. Now on to part two, Trail. It lookes pretty similar when it comes to handeling on a bike but the approach is way different. Trail isn’t something you can simply measure with a protractor and determine if it’s right for your bike. Trail is measured in distante between two fictional points. Just check out the picture below and let it sink in for a while.
Looking at the picture you can see that trail is measured from a fictional point on the ground to the center of the axle measured on the ground. The first point is found by extending an imaginary line from the frame rake to the ground, at least that is when you use frame cups without any offset/angle. To be precise it’s the imaginary axle on which the front fork pivots. The second pint is fount to draw an imaginary line from the axle of the wheel to the ground. The distance between those two points is called trail.
Trail has a way more dramatic effect on handling than the rake angle. The basis principle is the same. With trail you lenghten or shorten the wheelbase of the bike making it harder or more easy to turn. Thing is, trail does it directly, since you’re acting upon the position of the wheel itself, instead of it moving because of the change in angle. It’s understandable that working on the trail of your bike can make a raked out chopper handle just fine when you find that sweet spot with the trail but can also make a bike make very hard to drive due to a a wrong trail. The basic principle is the same as with rake. More trail gives you more wheelbase and you get a stable bike at high speeds and lazy at low speeds. Less trail gives you the direct opposite.
Normally Trail is positive. Which means that the point measured from the axle of the front wheel lies behind the point measured from the steering axle. But it can also be negative due to the use a wrong fork in the frame without adjusting the frame rake. This is a situation that should be avoided at all cost since it gives you a false sense of security. The bike will handle perfect at low speeds but can become unstable on high speeds and due to the smallest inpurity in the road causing you to kiss the asfalt or even worse.
As in the case with rake, the amount of trail varies with the type of motorcycle. The 9-15 cm in range is what the experts say is the perfect amount. Keep in mind that trail has to be in sync with the rake angle, as the combination of the two can make or break your setup.
A little bit more theory: Offset
With the basics done its time for our biggest influence in the trail of a bike, the offset. When looking on a front fork you’ve probabaly noticed that the steering stem isn’t in line with the fork tubes. Most of the time the fork tubes are placed slightly further to the front than than the steering stem that is in the frame/ The distante between these two is the offset. Offset is not only the distance between those two lines but in some forks even the angle between the tubes and the steering stem is different. All are done by the manufactor to find that sweet spot between the rake and and trail of the bike.
By adjusting the offset or the angle of the offset you can directly influence the trail of a bike without adjusting the rake of the frame. One well know method are the adjustable triple trees. This way the frame rake stays the same but the trail is adjusted. If this is done with trail in mind and some extended fork tubes this may reslut in a vcool looking bike. But when it’s changed dramaticly it will be resulting in a negative trail. Looks pretty rad but a pain in the ass once cruising down the freeway.
Adjusting Rake and Trail.
Before you start adjusting your your rake an trail there are still a few things you need to keep in mind. When you do small adjustments on you bike, like changing your front wheel, you immediatly adjust the rake and trail of your bike. For instance changing the front wheel from a 16″ to a 21″ wil lift your steering head slightly and therfore change the rake. With the rake slightly changed the trail has also changed a litlle. Same goes for going for longer inner tubes. 6″ over forks look awesome but do have an effect on the handling of the bike since the neck of the frame is raised, rake has changed and therefore the trail has changed.
Like mentiond before the length of your fork and diameter of your wheel are ways to influence the handling of your bike. There is one more just spend a few minutes on figuring out what suits you and you’re golden.
Note this is for hydraulic forks only. The basis rules as ar as Trail, Rake and Offset also apply on springers/girders but they have some additional theory. With springers you can adjust all of the above but also have to keep in mind a few new variables like Flop which can be adjusted by the lenght of your fork and the shape/size of your rockers. Flop also accures on hydraulic forks but the effect is minimal once you’ve got the trial/rake thing figured out. On a springer that is a completely different story, but more on that later in a new Tips and Tricks 🙂