On a fixed gear bicycle it is possible to mount only one gear, this must be chosen carefully to be suitable for every situation. In particular, a long ratio will favor driving at high speeds, on a straight line or downhill, however it will be very difficult to push in situations such as an urban environment or in the presence of hills. On the other hand, a ratio with a small metric development will be favorable in situations of acceleration, starts and relaunch, but with this it will not be possible to reach high speeds.
It is therefore necessary to reach the right compromise, which is very subjective both for the environment in which the bicycle is used, and for the characteristics of the cyclist himself. Usually those ratios that develop approximately 5 - 5.5 meters per pedal stroke (which roughly correspond to 42-18/16, which are in fact the usual ratios in sprint bikes) are particularly advantageous, as they manage to reach a good compromise. fixed.
the number of teeth of the pinion and the crown of the crankset constitute the PEDALING RATIO; on a fixed gear bicycle, having only ONE pinion and ONE crown, we will have ONLY ONE gear, therefore it is important to choose it according to our purpose. To do this, a mathematical operation introduced by Sir Sheldon Brown is useful, which calculates the "gain ratio", i.e. how many meters the bicycle will travel for each meter traveled by the cranks of the crankset. The formula is: Gain Ratio = wheel radius (including clincher )/crank length multiplied by the number of chainring teeth/number of sprocket teeth.
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