Confused newbie

Ok, I am now getting confused... Building up an old Trek 950 (vertical dropouts) into a single speed for commuting. It currently had an adjustable BB which is seized and i'm gonna replace this. Can I use a cartridge BB instead of the old adjustable, as I have all the tools for fitting this. I require a 68mm unit but need to decide what crank set to use before choosing axle length. I was gonna get a track crank set from on-one but they say I need a 108mm axle for correct chain line, but I can only find 107mm BB? Can someone far more knowledgeable than I clear this up for me?

Yeah use a cartridge b.b, it will be fine. 1 mm out shout be ok, but go speak to your lbs if your are unsure.

This b.b is 108 http://www.wiggle.co.uk/ProductDetail.aspx?ProdID=5360021112&referid=Frogoog

Bear in mind if you are converting a bike to single speed from a bike with a casset, the rear cog can bea easily moved around with spacers.

this seems such an obvious query (to you lot) i feel stupid asking, but i really don't get what CTC and CTT mean in frame sizing. Can anyone help. I mean I've read the descriptions i've found on google, but i still don't quite get it. How can they both be the same, as they are on some bike ad listings?

Um, they can't... not unless the seat tube is completely vertical.

Centre to Centre, Centre to Top. Centre of the bottom bracket to centre (or top) of the top tube.

you will have issue with a mtb frame because you won't be able to run a chainring over 37T otherwise your chainline will be out, as the chainring will hit the tubing, unless you crimp it ;)

Not according to the On-one site who say using a 108 square axle will work with their track crank on a MTB? Chain ring is 49T. Mind you, it's looking pretty tight, so I'll let you know!!!

i was looking into buying a single-speed mtb, but kept on coming up with the bottom clearance tubing problem ;) , even on the on-one singlespeed.

Well, i'll let you know how I get on. I like a challenge - like seized seat post!

squoocher ... thanks Platini, that's a very concise but very effective explanation. I think i get it now. By the way, scoring nine of France's 14 goals in just five games in their victorious 1984 European Championships campaign on home soil surely ranks as your greatest achievement in an illustrious footballing career.

Je préfère ai laissé le séjour passé fermement dans le passé, mais beaucoup de mercis de vos mots aimables…

tomiskinky Not according to the On-one site who say using a 108 square axle will work with their track crank on a MTB? Chain ring is 49T. Mind you, it's looking pretty tight, so I'll let you know!!!

tomiskinky Not according to the On-one site who say using a 108 square axle will work with their track crank on a MTB? Chain ring is 49T. Mind you, it's looking pretty tight, so I'll let you know!!!

I emailed them about that because their site was confusing. They told me I could not get a 42 mm chainline they where set up for a single speed mbt chainline of I think 47 mm or 50 mm. Their stock changes though so the new batch may be different so email them to check.

Just move your rear cog around with spacers (that is if it is/was a cassette rear wheel).

Are you going to tun a chain tensioner ?

Yeah, gonna run a chain tensioner. I have the on-one singlespeed spacers and cog for the cassette, as thought this probably the best set up to run with the on-one front end?

if you run the cog on the outside of the cassette and the chainring on the outside you should be ok

Only got as far as putting headset on (that all works as it should - put in STX cartridge) BB is in too (Truvativ). I put the crank on last night and don't think it will touch when on tight as I can's see it going on much further!!! But you never know - need to get my hack wheels off the MTB and put the single speed bits on it and see how it all lines up? Waiting until I get some brakes (ebay - keep losing out on em... grr) but might just put the slicks on my Hope wheels for a few days so I can see if everything goes on in line?