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SPECIAL HAPPENINGS Health tip Emergency contacts: In your cell phone under ICE (in case of emergency) list a friend or relative so ER will know whom to call. (Consumer Reports, July 2007). Nanoparticles found in many sunscreens. Many sunscreens (eight out of eight) contain nanoparticles of zinc oxide or titanium dioxide, even though you won't see the term “nano” on the label...Nanoparticles create free radicals that damage DNA of cells and possibly cause other harms as well...and even low dosages of titanium dioxide can damage lungs of animals if inhaled. That said, if applied to live tissue such as a cut (or road rash) you are vulnerable to increased risk. It is prudent to avoid exposure to those nanoingredients by choosing sunscreens that don't list titanium dioxide, or zinc oxide on their label. (Consumer Reports, July 2007) Wednesday July 11 4/M/45-50 miles Al's Bakery Ride Shimmy or Speed Wobble Subject: 8h.5 Shimmy or Speed Wobble Shimmy, a spontaneous steering oscillation of the front wheel, usually occurs at a predictable speed when riding no-hands. The likelihood of shimmy is greatest when the only rider-to-bicycle contact is at the saddle and pedals. This position gives the least damping by hands, arms, and legs. When shimmy occurs on descents, with hands on the bars, it is highly disconcerting because the most common rider response, of gripping the bars firmly, only increases it. Shimmy is not related to frame alignment or loose bearings, as is often claimed. Shimmy results from dynamics of front wheel rotation, mass of the handlebars, elasticity of the frame, and where the rider contacts the bicycle. Both perfectly aligned bicycles and ones with wheels out of plane to one another shimmy nearly equally well. It is as likely with properly adjusted bearings as loose ones. The idea that shimmy is related to bearing adjustment or alignment has been established by repetition. Bicycle shimmy is the lateral oscillation of the head tube about the road contact point of the front wheel and depends largely on frame geometry and the elasticity of the top and down tubes. It is driven by gyroscopic forces of the front wheel, making it largely speed dependent. It cannot be fixed by adjustments because it is inherent to the geometry and elasticity of the bicycle frame. The longer the frame and the higher the saddle, the greater the tendency to shimmy, other things being equal. Weight distribution also has no effect on shimmy although where that weight contacts the frame does. Bicycle shimmy is unchanged when riding no-hands, whether leaning forward or backward. Among parameters that supposedly cause shimmy, spoke pattern and balance had no effect. Tests with wheels balanced and purposely unbalanced and ones with paired spokes as well as low spoke count caused no change in shimmy. Filling the front tire with water, doubling its mass, had no effect other than to change its frequency of oscillation slightly. Shimmy requires a spring and a mass about which to oscillate and these are furnished by the frame and seated rider. Unloading the saddle (without standing up) will stop shimmy. Pedaling or rough road will also reduce the tendency to shimmy. In contrast, coasting no-hands downhill on a smooth road at more than 20mph with the cranks vertical seems to be the most shimmy prone condition. When coasting no-hands, laying one leg against the top tube is the most common way to inhibit shimmy and also one of the most common ways to coast no-hands. Compliant tread of knobby tires usually have sufficient squirming damping to suppress shimmy. Weight of the handlebar and its extension from of the steering axis also affects shimmy. Shimmy is caused by the gyroscopic force of the front wheel whose tilt
is roughly at right angles to the steering axis, making the wheel
steer to the left when it leans to the left. This steering action Shimmy that concerns riders occurs with the hands firmly on the bars
is rider generated by muscular effect whose natural response is the
same as the shimmy frequency, about that of Human shivering. Jobst Brandt |