Chainline

[Brian]

i'm building a new bike for a friend and I like to do things right first time, so i measured a similar bike i bought new and bought the bottom bracket which gave me the same chainline, which was 51mm.

the bike is a hybrid with triple on the front so i guess mtb chainline would be more appropriate than road, but according to sheldon brown . i'm way off, anybody got any suggestions

[cyclerUK]

Chainline is the reach of the front derailleur to operate the chain.
So your guess about MTB chainline would seem correct. Personally I have never bothered about chainline and just get the chainset as close to the BB as possible.
If you are using Shimano gear then their technical website will give you the chainline.
http://techdocs.shimano.com/techdocs/blevel.jsp;jsessionid=pv1SLTjbLRVPgSFBTN20zr3FfHsRp8NFMLxBv1z1hnXFpQFvjJKh!-1437688368?ASSORTMENT%3C%3East_id=1408474395181679&FOLDER%3C%3Efolder_id=2534374302051113&bmUID=1259250683733

Shimano's MTB/Trekking chainlines are usually 50mm.

[nfmisso]

Chainline is the alignment of the front chainrings with respect to the sprockets on the cassette/freewheel.

Different front derailleurs have to match the chainline you build so that they have sufficient travel to move the chain to the desired rings.

Personally, I pretty much let things fall where they will, and so far it has worked out okay......