It would have been uncommon to find a cassette as large as SRAM’s Eagle 10-50 a few years ago. Alex Evans You may be on a racing team which needs to have all the bicycles equipped the same, for easy parts interchangeability and to match pedaling cadences.

There are new rear derailleurs on the market that are identifiable as being compatible because they have a ‘520% range’ graphic printed on the derailleur cage. SRAM Eagle AXS rear derailleurs are compatible with the new 10-52 cassettes. Grayed-out rows in the table below indicate cassettes not listed in the 2015 new-products listing or 2016-2017 catalog. SunRace appears at this time to be specializing in MTB cassettes, at least among the 10-speeds. SunRace does not give tooth counts in the 2016-2017 catalog but there are tooth counts in the earlier catalogs. SunRace listed a 12-32 10-speed cassette in the 2013-2014 catalog but did not give tooth counts for it. The cage of a rear derailleur is designed for a certain range of gears. For example, Shimano’s outgoing Dura-Ace R9100-SS rear derailleur is designed for use up to an 11-30 cassette.This saves weight and, since it isn’t subject to wear from the chain, the carrier is often made of a lighter material – carbon fibre in the case of Dura-Ace cassettes

Unless you’re running a triple crankset, it’s unlikely you’ll want to use a road bike cassette on a mountain bike. Dave Caudery / Immediate Media You need to ensure you’re using a compatible rear derailleur if you’re using the 10-52 option, because the previous-generation Eagle mechanical rear derailleur’s cage is slightly too short.If you are specifically using a Shimano HG freehub, you need to consider how wide the cassette you are buying is. Road wheels have slightly wider freehubs than MTB ones – by 1.85mm – and 11-speed Shimano HG road cassettes are slightly wider than 8- or 9-speed ones, again by 1.85mm. Shimano’s HG freehub design was the most common option for many years. Felix Smith / Immediate Media Grayed-out rows in the table below indicate cassettes which were listed in the 2011 catalog but are no longer listed in the 2016 catalog. If you wanted to use an 11-34 cassette, as well as buying the relevant cassette, you would need to buy a compatible rear derailleur. In this example, it would be an Ultegra R8050-GS or 105 R7000-GS rear derailleur. The GS denotes that these are ‘medium cage’ derailleurs. The same rule applies to Shimano Di2 derailleurs.

You may sometimes see brands refer to their cassettes as having a certain range in the form of a percentage. Please also note that we highly recommend fitting a new chain with your cassette. This is because chains and cassettes wear sympathetically with each other.Some people may wish to use a road bike cassette on a mountain bike or vice versa. Here, we’ll go over why you may (or may not) choose to do so, and look at the compatibility issues both options may present. As of this writing, Harris Cyclery does not sell IRD cassettes, but they are included here for the sake of completeness -- John Allen.