2x11 to 1x12 upgrade help

[OnTheRicky]

I'd like to upgrade my wife's bike to Eagle so it fits on my Kickr with an Eagle cassette. 

The bike is currently running a Shimano SLX M7000 2x11 groupset with some other components:

Cranks: Shimano SLX FC-M7000-11-B2 (170mm) 

Bottom Bracket: Shimano BB-MT500-PA, 41x92mm shell

Cassette: Shimano SLX CS-M7000, 11-42 tooth

Hub Rear: Syncros XR2.5 CL / Boost 148x12mm

I'd prefer to upgrade to GX, since I've read and heard lots of bad things about the quality of NX derailleurs and shifters.

The three issues I have are that 1) I need to keep 170mm cranks and 2) I need to change to a XD freehub (or not) and 3) I have no idea if that bottom bracket will work with Eagle cranks if I need to change. 

The XD freehub is the easy part - I know I can simply stick with the NX cassette (this is probably an okay compromise) and I think the Syncros hub can be changed to use a DT Swiss XD freehub if I do change to the GX cassette. 

 

Where I need some help is with the crankset. I don't think that any GX Eagle groupset kits come with 170mm cranks as standard. What are my other options for cranks? Is there any way to keep the existing SLX cranks and fit a 1x12 compatible chainring?

If I do end up getting the 170mm GX/NX Eagle cranks, will they fit that Shimano BB? 

 

[Fitbull]

Hi Ricardo, I changed my wifes bike from a 2x11 to 1x12 but I only put on the Eagle shifter and derailleur. I went with a sunrace 12 speed cassette in order to not have to get the XD freehub. This was in the days before NX.

 

I also didnt change the cranks, I took the one chain ring off the crank and just put a 32 where the big chain ring is currently. I did have a problem with the 32 chain ring because it is just a bit too small and where the crank arms met the chairing it would push the chain off the chain ring. To overcome this I then put in a small spacer so the crank arms and chain ring were separated and the chain doesnt come in contact with the arms..

 

This has worked an absolute charm but only if your wife is happy with a 32 tooth chain ring of course. If you want a 30 you will need to change the crank. Sorry I cant help on the 170mm crank side.

[ChrisF]

At the rear - going with NX or Sunrace is the easiest and cheapest solutions, though I would still get a decent derailure.

 

 

In front - changing from a 3x to a 1x is much easier, as you replace the middle ring with the one of your choice, and the ring lines up with the rear.  From 2x it is a bit more fun to get the front blad to line up with the middle of the rear cassette ... you may need some spacers ..

 

 

How much thought have you put into the selection of the front ring ?  Do you know what climbing gear she "needs" ?  Do you know what top speeds you do, typically not an issue on the trail but may well be an issue if you ride on tar to the trails ....  Well worth spending some time here : http://www.ritzelrechner.de/

 

We are busy changing a 3x9 to a 1x11 (jip, you need the 1x12).  Playing with the gear charts we could confirm the 32 in front gives us the same climbing as needed, but at a loss of 5% top end.  In this case the top end is not an issue.  Worth noting that the 1x11 gives us the same 11/50 as the NX, in the middle two gears jump by three teeth instead of 2.