Wednesday, November 10, 2010


What is this, math class?

Well, Geometry is important for bicycles, due to real-world physics and engineering. That's why we often post the geometry numbers for bikes, when available.

For people who want to use a bike for transportation around their city or town, or for short recreational rides, an upright riding position can be more comfortable, safe, and easy, compared to a leaned-forward racing or mountain biking position.  We've talked about how to get an upright ride before. Some things can be done on most bikes, like changing the handlebars or stem, moving back the seat or changing the seatpost. However, the shape of the frame limits how far these changes can go.

For rider position, the most important facts are the position of the bottom bracket (the axle that connects both cranks, and therefore determines the position of the pedals) in relationship to 1) the seat, 2) the ground, and 3) the handlebars. On a long-distance touring bike you may want "drop" handlebars, with the tops level with the seat. A mountain bike used on trails will likely be set up the same, but with flat bars. For these activities, it is worthwhile to have some of your weight on the handlebars, to help with steering, and to relief the seat of some of the weight. Road racing bikes, with triathlon and time-trial bikes being the extremes, have the bars even lower, and the seat farther forward, for very leaned-over, aerodynamic position.

On the other hand, 3-speed roadsters were made for years with the handlebars swept-back, with the grips a couple of inches above the level of the seat, which was also further behind the bottom bracket. The dutch-style bikes of Europe, and American Cruiser bikes often had the handlebars even higher and further back, up to a foot above the seat, with the pedals far forward. This allows a fully-upright rider position, with the arms down at the sides, yet keeps the angle between the torso and pedals appropriate for good use of the leg muscles.

When American bike companies rediscovered the market for these sort of bikes in the 1990's, unfortunately, they developed the so-called "hybrid" as a mix of Mountain Bike and Road Bike characteristics, meant for occasional recreational cyclist. Hybrid bikes had the seat almost over the pedals, fairly low handlebars, usually straight in the mountain bike style (sometimes not even adjustable), and skinny road-style tires. 

Around the same time, the beach cruiser was revived in North America, showing pent-up demand for more comfortable, upright bikes. And updated hybrid, the Comfort Bike, was born. It used a frame about the same as a hybrid, but moved up the handlebars, often adding a suspension fork, used wider tires, and a big, soft-looking seat. Unfortunately, these bikes still usually have the seat too far forward for such an upright riding position, putting all of the effort of the thigh muscles, and none on the gluteus. 

Clever Cycles made diagrams of rider position on different types of bikes in their "Dutchness" article.  The road racer is depicted as hunched over the drops while, at the opposite end of the spectrum, a recumbent rider is leaning way back.  In the middle are the comfort bike rider and Dutch rider, sitting upright on their bikes.

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