I have just replaced my 11-32 10 speed cassette with a 11-34 to get an extra granny gear.
Playing around with the Sheldon Brown gear calculator and reading the specs on my rear derailleur (Shimano 105 RD-5701 GS), I have calculated that I am out of spec for the RD, and have been so with the 32 granny gear, although everything has worked and shifted just fine.
10 speed bar end shifters
Triple crankset: Deore 48-36-26
Shimano's specs and my set up in brackets:
Max low sprocket = 30T (34T)
Max capacity = 40T (45T) calculated: (48+34)-(26+11)=45
Should I have concerns, or are Shimano's specs conservative?
Yes shimano's specs are conservative. If you can live with coasting down hills I would get rid of the 48 chainring.
If your bar ends are 10spd road, not MTB or road tiagra 4700....
Shimano RD-3040
Shimano CS-M4100 11-42
Crankset 22/36 or 22/30/40