The Naive Bike


In the next quest to determine more about the role of bicycle design as well as front fork geometry, it was decided to construct a bicycle with what we’ll call a naïve front fork. The frame has been modified to move the steering head forward, and to have the head angle be vertical (and thus at 90 degrees). Next, a front fork was created that caused the trail to be zero, that is, the point of contact with the ground coincided with the axis of rotation of the front fork. As a consequence, the friction and contact forces as might ever exist between the tire and the ground will act coincident with the axis of rotation of the front fork. Thereby no moment arm exists to induce any significant ground force generated turning moments on the front fork about the steering axis. We called this the Naïve Bicycle, as the bicycle is naïve in behavior and has no predisposition for the front fork to turn in spite of what the bicycle dynamics might be or even according to how the bike tilts.
Concerning the matter of gyroscopic actions, the use of two 12.5 inch tires mounted, one atop the other, caused a cancellation of all front fork precession as well as gyroscopic effects. Other than rider exerted torques by placing hands on the handlebars, this bike has been designed to have scant front fork torques. As a sticky point, we have not as of yet attended to the detail of counter-weighting the handlebars, so admittedly there would be a slight moment in turns due to the action of gravity tugging on the mass of the handlebars. Our plan is to replace the bent back handlebars with a circular-style steering wheel centered on the front fork axis. We note that the center of mass of the front fork is presently behind the steering axis, and thus if the Naïve Bike were to lean – the tendency of gravity action would be to turn the front fork away from the lean causing destabilization. To preliminarily test this shortcoming, the Naïve Bike has been ridden with the handlebars turned 180 degrees, in essence with forward center-of-mass, and the bike is still rideable. Another possible front fork torque could be argued to be due to aerodynamic actions; however we feel that aerodynamic aspects are not significant.

The experimental findings and significances of the Naive Bicycle are many. First of all, the Naïve Bicycle is easily capable of being ridden, meaning that an array of persons of relatively average abilities can and have ridden this bike. Another way to say it is that the bike has always been capable of having been ridden, as every person trying has been successful. Of course, the rider must keep hands-on. No able-bodied adult sized person has ever failed, and hundreds of persons have ridden this bike. The first inference is that precession is not essential in order for a bicycle to be ridden. The second inference is that front fork geometry and trail, in particular, are not critically imperative in order for a bike to be rideable. Moreover, as illustrated by the Naïve Bike, the combination of zero precession and zero trail of the front fork also result in a bicycle configuration that is easily rideable.

Close examination of the front fork on the Naïve Bicycle will indicate the presence of an additional tire axle slot. In short, the front fork was designed such that the two smaller wheels can be removed, and replaced with a single conventional full-sized front wheel. Doing so then restores the precession effects of the front wheel. Engineering students reported in experimental trials that this bicycle, with zero trail but with a conventional balloon style tire on front, was capable of being ridden “no-hands” by a skilled rider. The inference is that when sufficient gyroscopic front wheel action exists that (1) a controllable front fork torque can be induced based on upper body leaning, which in turn, causes a lean reaction of the frame of the bike, and (2) that the front wheel’s gyroscopic properties are sufficient to prevent or at least make controllable any front fork wobble.

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