Saturday, January 14, 2017

Minus Ten Review- 2

THAT trail, not "trail", get it?
Ten years ago on the blog I was talking about a wide array of things, but one topic that I covered is still sorely misunderstood ten years down the road.

You hear folks talk about how "None of this nit picking, micro-dissection of bicycles and geometry matters. Just ride!". Then you can find the same folks talking about how they really liked this demo bike they tried, or they really liked some different rig their friend has because it "felt so good to me!". "Say one thing, do another" much? Yes. Yes, many times they do .

One of these areas of misunderstanding is bicycle geometry, but there are others as well. Tires are another big one, but let's stick to the geometry for now, since that is what I was writing about ten years ago.

Front end geometry is probably one of the biggest contributors to how you perceive a bicycle handles. Rightly so, since your hands, two of five body contact points, are directly connected to the business end of front end geometry. They feel the results of what is going on with all those angles and whatnot. Yet many people fail to recognize this, or begin to understand how that can be such a big deal. Mere millimeters of difference in "trail", the measurement which describes the stability or lack thereof in a bike, can make a huge difference in your perceptions as a rider. Head tube angles are most often referenced in discussions about front end geometry, but that is really only a part of what really matters, which is the "trail" figure.

This post a decade ago ended up becoming the catalyst for an extensive experiment I ran a year later. I took my OS Bikes Blackbuck and ran eight different forks on it all with various offsets, axle to crown dimensions, and formats. (rigid and suspended) I made every effort to keep all other fit parameters the same. It was a very enlightening experience, but I'll leave that discussion for some time down the road.  


bostonbybike said...

I'm curious to hear more about your experiment. One thing that I'm still trying to figure out is how different the handling of such two bicycles could be:
Bike A - head tube angle of about 70deg, fork rake 45mm, trail 80mm
Bike B - head tube angle 73deg, fork rake 65mm, trail 40mm

Let's assume that everything else (as much as possible) is the same on both bikes and the front axle is in the same place on both bikes. In other words, both bikes have the same wheelbase, front-center, stack and reach but the only difference is how the steering axis is positioned in relation to the front wheel and frame.

Can anyone tell me what to expect in terms of handling in these two bikes?

Guitar Ted said...

@ bostonbybike- Pay attention to the end figure first- trail.

"Low Trail" bikes, like porteurs and other French camping/touring designs were designed to carry heavy loads on the front wheel. So "low trail", as in your "B" example, would steer very well when loaded down, say with a stack of newspapers, or two panniers and a big handlebar bag up front. Without the load, the low trail, (read "more unstable") would be a nervous-nelly bike. The front wheel would require a higher degree of attention to keep your bicycle on track than your "A" example.

In example "A", the higher trail figure means more stability. This is desirable on rougher tracks, mountain biking, or anywhere that a rider might want a bicycle to be a calmer experience. Of course, too much trail can be a bad thing depending upon the rider's preferences. "Slow", "sluggish", and terms similar to that are often credited to bikes with high trail figures. That said, there is a time and place where high trail is the way to go.

So, you can think of example "A" in terms of an American paper boy style bike vs example "B" which is sounding like a classic French paper boy's bike. American paper boy bikes used rear baskets to haul the loads whereas the French paper boy bikes used a big front rack. Therefore you get two completely different handling bikes with completely different front end geometries.

There are more nuances to consider than this, but trail figures are the basis of understanding a bicycle's handling "on paper". Nothing trumps an actual ride, but that said, trail figures are where you should look first for clues.