The Build Up: Frame Design, Where the Art Meets the Craft.
I’ve been researching the intricate details of frame design. The angles are one of those things that make or brake a bike in a way. For that it would be obvious that one would need to find the details specific to the angles, why, how, what for?
Turns out, there is no good way to explain it. No good way to study it. No completely concrete opinion as to what makes the best setup.
One of the issues is the complexity of the situation. Think of it like this. When you turn you have the frame of the bike you have the plane established by the direction of motion. Then you have the plane established by the frame of the bike as it is leaning. To add to that you have the plane established by the leaning wheel. This is three intersecting planes sharing only one common point.
Then we can also add the complexity of the fork and wheel combo. A bicycle wheel if turned makes a sphere but if it is attached to a bicycle fork at and angle it cuts out a path more like a donut. So it isn’t like a Dyson Ball vacuum. It is far more complicated.
First thing a bicycle only turns it wheels more than one or two degrees at or below nine miles an hour. Under most circumstances likely less. Any time the wheel is rotated more than a few degrees at a speed greater then that would cause the bike to flip over the front end. When the bike leans the action of leverage creates a lead in that pushes the back end of the wheel. this is why under really fast riding it is commonplace to see advanced riders actually turning away from the turn or counter steering. It allows the frame of the bike to drop in more and allows the wheel a quicker recovery from the turn and rights the bike and ride faster.
It seems that the steering angle does have some effect on handling in the manner of how it actually allows this. The actually greater effect is found in fork rake, but only in the manner of its relation to the overall diameter of the rolling wheel. The lower the ratio, or more accurately the closer the quotient of diameter over rake is between one to three, the better the handling the bike will be. This is all related to the overall steering angle as well, That is to be sure, but how and why is actually more unknown than we would like to admit.
The truth of the matter is that stability, while aided by wheel base, is not predicted by wheel base. Nor is nimble handling, for that matter, determined by fork rake or angle.
I have mountain bikes that can turn on a dime, for that matter I have a match sprint frame I built that has a 75 degree head tube and a 25mm fork rake that dives into corners but hold a line better than any bike I have owned. I’ve ridden miles,hands free on training rides (it’s my favorite bike, the first I built) while shuffling through my pockets, jostling my courier bag, writing emails on my smartphone, (we’ve all done it) and weaving in and out of traffic without ever touching the bars.
This is where the divide (or possibly the junction) between art and craft is most important. I is the eye and the hand that makes a bike ride, and ride well.
I can only explain this best as like the actions of a chef in the kitchen. The characteristics of a bike are like the characteristics of different foods. The styles of ride, much like different cuisines.
The skill is in the proper manipulation.
So again, what are you looking for in a bike? What do you want in a frame? What do you look for in a ride?