SRAM PG990 9 Speed Cassette

About Cassettes & Freewheels

Cassettes and freewheels for bikes are a cluster of sprockets in a range of sizes offering a multitude of gear ratios. The difference between the two is, a cassette slots onto the freehub, which has the ratchet built in and is then secured with a lockring, whereas a freewheel is a cluster of sprockets built around a ratchet and threads directly on to the hub. Cassettes and freewheels come in many ratios, close ratio is when the number of teeth increase in small increments of 1 or 2 at a time, whereas a wide ratio is when the teeth increase in larger increments of 3 or 4 at a time. Most systems will use a cassette hub as these allow for a wider bearing spacing and increased axle life, you can also fit a larger quantity of sprockets onto a cassette hub with 11 speed systems now becoming available. With cassettes you must use the appropriate spacing for your gear levers and rear mech, Shimano and Campagnolo are not interchangeable so you will need to match the cassette to your levers for smooth and precise shifting. Sram and Shimano chains and cassettes will work together as they use the same spacing.