Shimano Deore CS-M5100 cassette

11 of your finest speeds

With the current war of ratios that is going on between Shimano and Sram over who can shoe horn the biggest sprocket onto their 12 speed cassettes ,at time of writing, Sram has gone one better with 52T over Shimano who introduced 51T just to outdo Srams 50T from a while ago…phew! it was refreshing to see that there are options further down the price scale that don’t need a specific freehub to work. Shimano 12sp needs their propitiatory “Micro Spline” freehub and in turn to run Sram big cassettes in most cases you need their “XD” driver.

However if you haven’t invested in the 12sp technology yet and are still running 11 speed then there is now a very good alternative from Shimano. The Deore M5100 cassette which happily fits straight on to the standard Shimano freehub that everyone running the big “S’s” gears already has. Before this new cassette the biggest sprocket on a 11sp Shimano cassette was 46T which is a very low gear indeed and originally ideally suited to a mountain bike. It does suffer though from a hug gap between the penultimate sprocket and that 46t, namely 37t-46t. I ran this cassette through the winter months on my gravel bike on a set of 650b wheels with much knobblier tyres than those I use in the drier months as my local terrain is very muddy and clay rich so i need all the traction i can get for the seated climbing necessitated to stop the wheel from spinning out. The gap was very annoying and when I needed a slightly lower gear than the 37t to stop stalling (I’m no climbing super hero as you can tell) the big jump to 46t was too great and I ended up loosing balance as my legs spun wildly.

The solution pt1

to over come this i butchered a 11-42t cassette, removing the 15t sprocket and adding a very second hand expander sprocket which used to be all the rage before huge cassettes but seem rare these days. This sprocket had 45 teeth so making the final jump between cogs 42-45t which was much better and this is what i ended up running for most of the damp months. Unfortunately the horrible gritty/grinding local conditions all but destroyed the cassette and chain (ok, i should have checked the chain wear more regularly) so knowing that the new Deore cassette was imminent I nursed that chain and cassette for as long as possible until my local bike shop called to say the new cassette had arrived!

The Solution pt2

The Deore M5100 has a ratio of 11-13-15-18-21-24-28-33-39-45-51T and those last 3 sprockets are very evenly spread so even tough the gaps are bigger than at the other end of the cassette the transition is easier to keep a good cadence on and aids balance and traction as your legs aren’t all over the place when concentrating on traction and line choice. The smaller sprockets are much closer in range and this is a good thing as on a gravel bike this is where you will mostly be sat. Small ration changes enabling smooth pedaling and letting you carry your speed on tarmac and less technical off road sections. the new cassette was 70g heavier than my modified 11-45 extended cassette)


M5100 in action

When I came to fit the cassette I was expecting to have a fight to get it to work, probably requiring a rear hanger extender/road link but i thought i’d try it out first anyway. I did fit a complete 116 link chain ( the old one was left this long too to accommodate the 11-45/46T) , set the clutch to on and with trepidation cycled through the gears. As you can see from the video, I was lucky and it worked straight away without any modification. I didn’t even have to adjust the “B” screw it was fine on the setting from the previous cassette. Please note if you try this your set up may be different! it’s not my fault if you damage anything!

So there it is, as mountain bike cassette on a gravel bike. the rest of the gearing is all GRX 810 with a 1 x 40 chainring. the 51t sprocket gives very very very low gearing and other than deliberately trying it out when riding I doubt if I’ll ever use it on this bike. the next sprocket down tends to be my extreme sit and spin gear. However for a heavily laden touring or bike packing bike that has done away with the fuss of a double (or triple) chainset this could just be what you are after at the end of a long day with that last long steep incline to grind up.

The cassette has now done a couple of hundred miles around my local area and is so far trouble free so I’m in no hurry to swap it for something less silly. in fact i’m going to get one for my mountain bike as the cost of the cassette is much less than the cost of upgrading to 12 speed to get that extra gearing and who needs that extra one tooth (sram)?