First: “what the fork is a bike’s rake and trail?!” you might be asking.
“Rake” refers to the angle between the bicycle’s front forks and the ground, and is also known as its offset.
“Trail” is the distance between the pivot axis of the fork and the centre of the contact patch of the front tire at the ground. We will go into more detail below about how to measure this, just know that trail is one of the most important determiners of your bike’s handling characteristics.
Table of Contents
- How to Measure the Rake of a Bike Fork
- Next, Measure Your Bike’s Trail
- Why Care About a Bike’s Trail?
- How Does Fork Rake Affect Handling?
How to Measure the Rake of a Bike Fork
Measuring the rake of a fork takes a little mental gymnastics – here is the easiest way to figure it out:
- First, draw an imaginary line that follows the steer tube of the fork.
- Next, following the same angle as the first line, draw a line through the middle of the drop-outs of the fork – the slots where the front wheel’s axle sits. The distance between the two lines (measured along a third line which runs perpendicular to both) is the rake of the fork.
By itself, rake means nothing. When installed on a bike, a fork’s rake will alter the bike’s trail – which is again easier to measure than to explain.
Next, Measure Your Bike’s Trail
Having installed your fork on your bike, and added wheels, tire, etc., follow the first imaginary line above (which will be following both the fork’s steer tube and the frame’s head tube) to the ground. Now, draw a vertical line from the middle of the fork’s dropouts to the ground – which is where the front wheel touches the ground. Measure the distance between the two points on the ground and you have the bike’s trail – the distance by which the front wheel can be said to “trail” behind the bike (or at the least the bike’s fork’s theoretical point of contact with the ground). The rake of a bicycle’s fork is one factor in determining its trail, with the others being the angle of the frame’s head tube and the size of the wheel (including tire).
Why Care About a Bike’s Trail?
All other things being equal, the less rake the fork has, the greater the bike’s trail – and vice versa.
As a measurement, a bike’s trail is an important determiner of how it will handle. The greater a bicycle’s trail number, the more stable its handling.
Inversely, the lower the bicycle’s trail number is, the more maneuverable or “twitchy” – that is, the easier to overcome its tendency to go in a straight line – it will be.
So why didn’t the sales guy at the shop where you bought your bike tell you about trail? If it affects the way your bike handles, you’d think it would be something that you want to know about, if not choose, right?
Well, the fact is that most bikes have a pretty standardized amount of trail.
For a given type of bicycle, you want a particular kind of handling.
A bike with lots of trail will be directionally stable: it will tend to go straight and be easy to ride hands-off even when the road is a little uneven. Such a bike will take more physical effort to steer than a bike with less trail.
For example, touring bikes should be pretty stable, while a racing bike should be more maneuverable.
If someone tried to design a twitchy touring bike or a racer that handled like a truck, they’d quickly be out of a job.
How Does Fork Rake Affect Handling?
But if you did want to change the handling characteristics of a given bicycle, one (and probably the easiest) way to do it would be change to a fork with a different rake.
Just remember, trail and rake have an inverse relationship.
High Rake = Less Trail = Less Stability but More Responsive Handling
Road bikes and bikes with narrower handlebars are built for better handling.
If you changed the curved fork on your road bike to a straight one that followed the same, steep line as the frame’s head tube, your bike would actually become more stable, and less responsive.
Low Rake = More Trail = More Stability
On the other hand, should you select the fork with the least amount of rake, you’re effectively building a “randonneur” — a bicycle that’s meant to be ridden at speed over long distances. For such an application, you’d want something stable, and a low-rake fork provides lots of trail. Cruisers and touring bikes are examples of bicycle styles with more trail.
A mid-rake fork will perform reasonably well for both stability and responsiveness. . . but where’s the fun in that?