axle length when using single speed

i am replacing my hollowtech II with sq taper BB (and hopefully middleburn crank)
Plan to run only single chainring at front.

Does axle length not really matter (113 or 118)?

i am assuming the narrowere of the two would be sufficient.

please advise/confirm

depends if the chainring is going to scuff on the frame with the shorter axel.

its dependant both on the cranks, AND the frame.

though the crank should specify, and as long as you are not wedging a 42t chainring on the middle ring position, it should be fine.

For middleburn cranks the “standard” chainline of 48mm is acheived with a 113mm BB.

However, with a singlespeed set up its is less important if you can move spacers around ont he hub to place the sprocket in line wherever the chainline ends up.

Personally on my bikes (both are SS) I run Middleburn at 113mm BB axle with the chainwheel in the outer position (aesthetically more pleasing than in the middle position) giving a 54mm chainline which suits a rohloff sprocket, and with correct spacing also the SS.

113mm Sq Tpr here too – RF crank, rings in the middle position – 32t mtb and 44t on the commuter.

Cassette hub tho’ so I can move the spacers around to get a good chain line…