
Fixed Gear Skid MarksSkid patch numbers are a concern unique to fixed gear bikes, where the horizontal position of the pedals lines up with a fixed number of tire/ground contact patches. The fun of leaving a skid mark comes with a price, namely increased tire wear. Logically, it makes sense to spread the skid wear across the surface of the entire tire for maximum tread lifespan. This is where skid patches come in. The number of skid patches is determined by the given gear ratio and is easy to calculate. Assuming you skid with the same foot forward each time, it is the denominator of the reduced fraction of the gear ratio, starting with the number of chainring teeth as the numerator. In other words, a 48x18 ratio would be 48/18, reduced to 8/3, yielding 3 skid patches. 48x17 doesn’t reduce further, and has 17 skid spots. The rare rider who skids equally often with either foot forward can double their skid patches with ratios that reduce to fractions with odd numbers in both slots. Practically speaking, once the number of skid patches enters the double digits you’re in the clear as far as tire wear is concerned. The single digit combinations shown in the chart below are the ones to avoid. It is a foul sentence handed down by the bicycle powers that be that a vast number of complete fixed gear bicycles come equipped with a 48x16 or 48x18 gear ratio, sending many tires to an early grave. Choose wisely, or forever rotate your tires. 
