I'll try to be concise here, but lots of numbers coming your way...

Currently running Shimano 1x11spd, 11-46 cassette with RD-M8000-GS rear dr. The three lowest sprockets are -32-37-46.

The derailleur specs indicate 40T as the Low Sprocket Min. https://bike.shimano.com/en-EU/product/component/deorext-m8000/RD-M8000-GS.html

I'd like to change to a 11-36 cassette, and I wonder if the rear dr will work as designed. I don't see why it wouldn't - it works just fine on the 37t sprocket, as well as all the smaller gears that are on the cassette.

Thoughts? What am I missing? Is something going to bite me in the rear-end if I switch to an 11-36?

Thanks for your help.

2 Answers 2


The idea with the minimum tooth count for the low sprocket is the b-gap (distance between the guide pulley and the cog) has limits to how far in it can be adjusted. Exactly how far off it will be with this particular RD on a 36, I cannot say. (I wouldn't be optimistic since it can handle a 46 in 1x mode, which is much bigger than a 36 - I think the b-gap with a 36 is likely to be pretty ugly). Dropout design could also add some variance when pushing things in this way.

Slant parallelogram rear derailleurs move the guide pulley along a diagonal path as the derailleur moves. On your current cassette, the angle of the slant has determined what the b-gap is by the time it reaches the 37t and smaller cogs. If the b-gap were bigger than optimal on the 36t on the proposed 11-36 cassette, that overly big gap will then be replicated down the line.

Note also that 11-speed 11-36 is purely a SRAM thing. No Shimano groups have used it.

  • 1
    Thanks for such a clear explanation, Nathan. Sounds like I'd need a new rear dr and shifter if I want to run a smaller cassette, which is more than I want to invest at the moment. Take care!
    – Bob
    Commented Sep 10, 2022 at 14:11

This configuration may need to be tested to see if the b-gap issue that Nathan clearly identified is truly an issue. It may be an issue, but it also may not. If someone else has tried it and has been successful, that would be a good indication that you would possibly find success as well.

The real test going outside the Shimano-declared boundaries is to simply pop on the 11-36 cassette and see how it performs, and see if it can be adjusted to work satisfactorily for your setup (see if you can borrow one, or if a local bike shop will let you try it out without commitment to purchase if it won't work). Shimano has typically been a little tight on their recommendations for some of their limits. I currently run without any issue the same 11-36 cassette on my gravel bike using an 8000 series Ultegra GS rear derailleur, which Shimano only rates to a 34-tooth maximum capacity. Granted, my example is going the opposite direction, but it is an indication that there may be some range beyond the Shimano limits for what you want to do, and there are other examples of successfully going a little beyond the limits out there as well.

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