Upgrading 3x9 to 1x12 Shimano I have an old 26&quot; hardtail that I want to convert to Shimano SLX 1x12 (M7100) from its current 3x9 drivetrain. As the new 1x12 uses a micro spline hub, I am thinking of changing my rear hub from M475 to
FH-MT500 (micro spline QR 135). Would I be able to use my old wheel and spokes with the new hub, as both the hubs are Shimano and have almost same dimensions/flanges, etc. I can't find new 26&quot; wheels that have the microspline hub.
Or is it better use a Sunrace 11-51T cassette that uses the old Shimano HG hub? If I go this option, I am guessing I won't get the Shimano HyperGlide+ smooth shifting.
Also, is it possible to use a 32T narrow wide 104BCD chainring in place of my current middle chainring keeping the same crankset/BB. I can remove the smallest and largest chainring from my current crank.
Be careful about the expense. 26&quot; makes this a 10 year old bike. While each change over that time has been small, end result is geometries and performance of bikes have significantly changed in that 10 years,  My sons entry level $1k softtail is in many ways a better bike than my 9 year old Carbon Scott Spark 10. The cost of the upgrades and selling the old bike would go a long way to a new bike.
Unless the old rim is in excellent condition, threading a new hub onto an old rim can be difficult to get a good build. Personally I would avoid doing if at all possible. You would be better to buy a new (new old stock) 26&quot; rim. (The rim cost will be small compared to the labour of wheel building and new spokes. In the unlikely event the  old spokes are the right length, reusing 10 year spokes is not recommended.)
The Sunrace 11-51T cassettes are not bad, provided you use the right one. Ideally stick to the same manufacturer if you want bet performance, which means micro spline if you want 12 Speed Shimano
Have you considered 11 Speed?  You can get an 11-51 in Deore.
You can replace the middle chain ring, you may need short chain ring bolts.  With narrow/wide you can probably remove the front derailleur and not drop the chain - but as always, YMMV.  The chain line will be correct.