Uphill vs. Downhill.

 

For most motorcyclists, enjoyment is somewhat limited by straight roads.  As such, motorcyclists head for where the roads aren’t straight.  Predominantly this means riding in the hills and mountains where road engineers are forced somewhat by the constraints of nature and have to design roads with corners.  If I had some background in psychology I could probably derive a hypothesis as to why riding on windy roads is more fun than a straight line, but it is suffice to say “it just is”.

The nature of mountain roads is that they change elevation and as such you are either going uphill or downhill.  I am sure there will be exceptions, but most motorcyclists prefer going uphill.  Here are my ideas as to why:

Uphill helps prevent too much speed. Corners can only be taken at a set speed.  This speed will vary on many factors including (but not limited to) grip levels, rider ability, corner radius, motorcycle design etc.  What happens if you enter a corner too fast?  Well… apart from an involuntary clenching of certain muscles one of two things are likely to happen.  Either you slow down, or you crash.  If you’re lucky you can substitute “crash” for “run wide” and then hope that “run wide” does not entail “meet on-coming vehicle” or “visit the scenery”.  Slowing down mid-corner is problematic.  It’s not impossible, but it is made more difficult by the fact that tyres are already closer to their maximum grip level due to forces at work in cornering. (Think of centrifugal acceleration)  When going uphill, gravity is your cautious friend.  It’s always working with you to slow the bike down.  When going downhill, gravity is more like the bad influence that used to get you in trouble when you were in school.  It’s there saying “yeah, go faster!”

Going uphill gives the bike a rearward weight bias.  As seen in Biking 101 Turning Corners, the rear wheel helps you go around corners.  Whilst the front wheel changes your direction, it is the gyroscopic forces acting upon the rear wheel that keep you turning through the corner.  Gentle mid-corner acceleration can be used to aid weight transference to the rear wheel.  It works whilst going downhill too, but it takes more acceleration to get the same effect, so you’re left in an awkward situation…  Remember the point above:  “Corners can only be taken at a set speed”. You really don’t want to be increasing this at a rapid rate when going downhill…  While I know and understand the theory behind the weight transference, I simply don’t think it is what I try and achieve when down-hilling.  Rather, the weight transference stays on the front, loading the smaller and more easily varied gyroscopic effect.  It is a lot of stress to be putting on the front tyre, but it is the same for all riders so you just have to put up with it.

Uphill corners have a natural positive camber.  Camber is the term used to describe the “banking” of the corner.  Where the outside of the corner is higher than the inside, the corner is described as having “positive camber”.  Look at a cycling velodrome, or a NASAR oval for an extreme version of a positively cambered corner.

A badly drawn image of a banked corner

Positive cambering makes people feel like heroes, because they allow for higher corner speeds.  The centrifugal acceleration that is attempting to fling you wide on the corner is partially negated by the ground.  Put another way, it’s pushing you onto the road, meaning you will be gripping it better.  Also, the lean angle (relative to the banked surface) will be less than if you are on a flat corner.  This generally means you have a bigger contact patch on the ground – again meaning more grip.  Unfortunately, there are such things as negatively cambered corners too.  Because they are banked away from the apex, they have the exact opposite affect: You have lower grip, greater lean angles, lower speed and less self admiration of your hero status.

A simple corner can be described in terms of “corner entrance, apex and exit points”.  For the purpose of this discussion, the most critical factor for a positively cambered corner is that the exit point is higher than the apex.  Conversely, a negative camber has its exit point lower than the apex.

If the road is level looking left to right, going uphill will make the road “act” like it has a positive camber.  Due to the uphill slope, the exit point will be higher than the apex.   Coming downhill has the aspects of negative camber.  The corner exit is lower than the apex. 

So, that is my explanation of why motorcyclists never tell you they are better going downhill, than up.