
Shapes and Angles
Bicycle frames must be carefully constructed to ensure stability, safety, and strength. Frames are often built with a rear triangle and a front quadrilateral. The angles formed are also very important. Bigger angles are necessary when speed is required. When comfort is more important, the frame is usually built with smaller, acute angles. Recently, there have been some very innovative frames that break all the conventional rules of bike design.
Gear Ratios
To build an efficient gear set, bicycle designers need to understand ratios. The gear ratio is the number of teeth on the front gear (sprocket) compared to the number of teeth on the wheel gear. If the sprocket has 60 teeth and the wheel gear has 10 teeth, the gear ratio is 60:10 or 6:1. This means that every time we turn the pedal, the wheel gear will make 6 complete revolutions. A 6:1 gear ratio is great for speed. Smaller gear ratios are better for climbing hills. Each rotation of the pedal requires far less force making it easier to pedal.
Wheel Geometry
Wheels vary in size but, in general, the circumference of a racing bike wheel is larger than that of a mountain bike. The larger the wheel, the greater the distance covered for each complete rotation of the wheel. The circumference is determined by the formula C = Pi x Diameter. If the diameter of the wheel is 27 inches, the circumference is 84.8 inches. Each time the wheel is rotated, the bicycle moves a distance of 84.8 inches. Performance Data
Bicycle components are put through rigorous tests to make sure they will be safe for cyclists. Frames are subjected to increasingly powerful forces and the amount of bend or stress in the frame is measured. This measurement is called the angle of deflection. The manufacturers must compare these deflection angles to acceptable ranges to determine the safety rating of the bike. Spokes are another critical bicycle part that must be carefully tested. The number of spokes used to build a wheel determines the amount of force each individual spoke must handle. An even distribution of force is necessary for strong wheels. 
