This is a switch from 9 speed to 10 speed.... I have a 10 speed FSA carbon crankset 52-39-30 I wish to run cassette 11-40 10 speed... I will size chain length to shift 39-40 and 52-30 no interest in running big big. Suggestions for rear derailleur and shifter. I have read that Shimano SGS long cage with B screw all the way in will shift to 40 cog. Thoughts?

  • 2
    You will eventually make a mistake and shift to big-big. Better to have equipment that survives it.
    – ojs
    Commented Apr 27, 2018 at 21:00
  • 2
    Its 2018 - 11-40 on a 10 speed is something you hacked together when affordable 11 speed was an oxymoron. I am unaware of any 10speed derailleur rated for a bigger cassette than 36. Mods such as Radcage and Goatlinks were common but still a hack.
    – mattnz
    Commented Apr 27, 2018 at 22:07
  • Why do you need such a large range. Many MTBers ride 1x, 11/46 is typical, and 10-50 is available and considered extreme. Your setting up the equivalent of a 1x running a 10/63 cassette.
    – mattnz
    Commented Apr 28, 2018 at 5:15
  • I am a bicycle tourist riding a recumbent P-38, I have an FSA hollow carbon 10 speed crankset 52-39-30. I am looking for a low of 19.5 gear inches. I could go for 52-39-26 but decided to with 11-40 cassette from IRD. This does give larger jumps than 11-36 but allows me to stay on 39 tooth middle on some climbs. I am ordering a MicroShift Mega 36-42 rear derailleur it looks like it should work well. I've used their front derailleur on a couple of bikes and been pleased. I also ordered their bar end shifters, which will index or friction with rear derailleur. Friction nice in emergency Commented Apr 28, 2018 at 5:44
  • Note that we don't do product recommendations, here, as they can be very regional and quickly go out of date. So what are you looking for in an answer? Commented Apr 30, 2018 at 12:55

2 Answers 2


For this setup you would need a derailleur with a capacity of (52-30)+(40-11) = 51 teeth. This page states that the SGS has a total capacity of 45 teeth. That's seems quite a bit below what you are trying to do, even if you don't plan on running big/big.

  • I just found a MicroShift 10 speed capable of 36-42 teeth large cog and wrapping 47t.... if we consider small small as 30+11 = 41 (which I never shift to) then 41 + 47 = 86 ..... which easily handles 39+40 (middle big = 79 t) .... then 52 + 34 = 86 which means only 52 + 40 is destructive... I am going with the MicroShift Mega 36 - 42. Commented Apr 28, 2018 at 1:11

Why change to 10spd? Why not just get an 11-40,9spd cluster, they are fairly cheap.

Go ahead and try it, you can always change back.

I got 3 sets of 11-40 suntour 8spd cluster, and changed them on families bikes using existing derailleurs.

2 of them work flawlessly, they are just ordinary shimano mtb type derailleur for 34T sprockets

1 is a bit marginal, and I might swap back to the 34T, if I can be arsed. So it isn't bad. That derailleur is noticably smaller than the other two, so not suprised.

I had to change the B screw for a longer one.

I am really happy with 11-40, basically I just ride in middle front sprocket now.

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