trail wrote:
AlexS wrote:
The relative variance in effective g forces experienced between straights and turns is a function of speed and turn radius, not weight. e.g. you might experience ~20% variance on a 333m track at these speeds (I haven't actually calculated it precisely, just a reasonable guesstimate based on other similar calculations).
Here's something I wrote about such things including a chart to show estimated g forces at different speeds on a 250m track:
http://alex-cycle.blogspot.com.au/2015/01/g-force.html
Thanks! Very interesting blog, and it clarifies the physics for me.
But I'm a little confused about the term "force." When you use the term "g force" you're not talking about force, but acceleration. Acceleration is a function of speed and turn radius.
And the force to counter-act that "g force" would then be proportional to mass, right? Given an acceleration (due to velocity, radius) a more massive rider will feel more force. Right?
Particularly in the case of an hour-rider who's going to be riding near the black line on the turns, very little banking to "absorb" the additional force? It is taxing. I've never done an hour on the track, but I know that if I'm sprinting along the black line at the end of a scratch race at near 40MPH, it takes a lot of physical effort to hold the turn correctly down there near the apron. It's not as noticeable in a 4K pursuit - less velocity. But I imagine if it takes a lot of effort in a sprint there must be some cumulative fatigue over an hour.
As I said in the blog, g "force" is a misnomer, it's really an acceleration rate. However the term g force entered the popular lexicon so long ago that it's become a ubiquitous way of normalising forces due to acceleration that we experience as "weight" to that which a human experiences when standing on the surface of the Earth.
The actual force is obviously proportional to the mass being accelerated (F=ma), but that's not what was asked, which was about the relative difference experienced while riding on the track. In other words, two riders going at 40mph on the track will experience the same g-force in the turns irrespective of their mass. That's because they are being accelerated at the same rate (and g-force is actually the rate of acceleration).
Put it this way, a 100kg guy normally "feels" the 100kg when standing, and of course will "feel like" ~150kg or so when travelling around the banking at speed. The 50kg guy will "feel" 50kg when standing and ~75kg when travelling around the banking at speed. Both are experiencing an acceleration of 1.5g.
The banking angle at the black line is the same as it is at the top of the track. Tracks generally don't have radially variable banking. It only becomes flatter on the cote d'azure.
The effort to hold a good line is minimal on well designed tracks and you barely notice the need to try and stay on line. On less well designed tracks, there can be a tendency to be pushed outwards a little and that create more tyre scrub. Such tracks are not generally fast as a result. There is a trade off with track radius and banking angle. The shorter the turn radius, the steeper the banking needs to be but that also means the minimum speed to ride safely increases.
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