Square Taper BB advice sought (and given).

Eyup.

I need to replace the bottom bracket in my 1998ish GT Tequesta. I'm going to put an FC-M442 crankset on it (http://www.chainreactioncycles.com/Mode ... elID=46021, bargain innit) and am not sure enough of how to interpret http://techdocs.shimano.com/media/techd ... 657937.pdf to know what bottom bracket to buy.

I think I need a 73mm shell for my frame (I'll check this before buying), but is it telling me that I need a 113 spindle? I don't know what my chain line is, or what I want it to be. I'm thinking of buying a UN55, 73 x 113, would that be sensible?

Also:

While we're on bottom brackets, I would like to advise everyone to avoid SunRace (as if this will be news to you...). My girlfriend had one. It worked perfectly for nearly 2 years with no play, but then a couple of weeks ago started clicking and within an hour fell apart completely - bearings all over the road. I had to tow her + bike + luggage the last 10km to a campsite in a town with a bike shop! Not the most helpful mode of failure.

The length of spindle needed is determined by your frame, well chain stays actually as each frame is different, so what works with one frame may not work with another!

If the bb you currently have is also a sq tpr fit the new crankset and see if you have clearance on the chain stays. If you have I'm sure that replacing the existing one with one of the same length would sort you out but....

If you have clearance but only just so, this might not be sufficient as when riding frames do flex and you don't want the chain rings crunching into the chain stay, but on the other hand you don't want the clearance to be big enough to be able to let the chain to get jammed or be able to fall between the stay and inner ring.

It be an idea so see if you could borrow some bb's from other RB'ers near to you so you can try out different lengths.

Good luck.

Aye, good plan. I'll try fitting the new chainset to the existing BB, and if that works, replace it with like. Ta!

yes either 110 or 113. good chance it is whatever length is in the frame already given the age of frame.

its saying here www.bikepedia.com/QuickBike/BikeSpecs.a ... l=Tequesta
that you have a 68mm shell
though SR AP-36 chain set means I have no idea of length. it'll probably have it stamped on the axle or written on the shell casing.

I've measured and it is indeed 68mm.

http://www.bikepedia.com/QuickBike/Bike ... l=Tequesta says 73mm but either it's wrong or that was a different version of the frame.

that's a 1996 I linked to the 1998 you mentioned

Which is why I think that it may have been a different version of the frame (my 1998 was only an "ish").

Someone will be able to tell you with a picture and/or serial if you wanted to know.