Bicycle Mechanics - conversion bottom bracket info

Hello everyone I'm new here but I've commuted by road bike for 3 years and I recently purchased an old trek elance 400 reynolds 531 road frame that included the fork and bb square tapered spindle, I intend to convert it to a fixed gear bicycle. My question is how to determine the size of the bb spindle in order to install the correct size crankset or if I would need to replace the bb spindle in order to convert it to fixed gear? The original crank info is: SR SXC-200. I'm quite lost at this stage. Any feedback is much appreciated.

Moved from SSFG.

The BB you need is determined by the crankset you use. You need to get the crankset first and then you can determine the BB length. Yes, you might be able to use the crank that came with the bike with the original BB. Do you have it? Roger

Moved from SSFG.

Why?

The crankset I have my eye on is an EighthInch 165mm silver crankset

The crankset I have my eye on is an EighthInch 165mm silver crankset
The crank maker should be able to tell you the recommended spindle length if you tell them the dropout spacing of your frame.

In the future, if you are looking at a new crankset, the Bottom Bracket (BB) size will always be included with the description; the recommended BB size for your cranks is 110mm ISO http://eighthinch.com/products/drivetrain/cranks/ Be advised that the ISO standard is different from almost all Shimano BB. For some reason Eightinch only sells one BB an ISO in 107mm, for their "Track" crank. 107mm might fit your Courier crank, but you would need to call to find out. If you want to buy from someplace else, make sure the BB descriptors says ISO or ISO Taper. The other (Shimano) standard is JIS, has the same taper but will mount about 5mm further out on the BB spindle, so you would need a very short BB Spindle to maintain the chainline. Miche makes a fairly decent ISO 110mm BB for about $35 but there are others, just Google 110mm ISO bottom bracket.http://www.amazon.com/Miche-Primato-Bottom-Bracket-English/dp/B001F6M30S/ref=sr_1_1?ie=UTF8&qid=1353696162&sr=8-1&keywords=110+iso+bottom+bracket

Anyhow Keirin /Track Spec frame with narrow dropout will have a different chainline than a
MTB or other conversion single speed with a 135 wide rear .

road frame could be anything from 120 to 130 depending on what the "speed' type was at the era it was made.

I sense It came with a BB. test fit the crank on ,

.. that included the fork and bb square tapered spindle ..

measure the chainline,
buy another BB axle length dependant on the data you gathered.

I do not have the original cranks but I measured the bb and it came out to 70mm. The maker is Sakae it's an 80s road frame 12 speed

I read other trek elance posts that determined the necessary bb would be 118mm or 115mm

I do not have the original cranks but I measured the bb and it came out to 70mm. The maker is Sakae it's an 80s road frame 12 speedIf your measurement is correct than you have one of old Japanese mixed standard BB shells; an Italian like 70mm shell, but with English (BSC) diameter and threads. The easiest way to fix this is to have an LBS trim 1mm form each side of the shell, so you will have a more commonly available size. But I would double check before you make any plans.



I read other trek Elance posts that determined the necessary bb would be 118mm or 115mmThat would be for the original crank (if it's accurate), not for the new crank you are buying; the frame determines the BB shell width, but the crank determines the spindle size not the frame..The 118-119mm would be for the SR SXC-200 crank that you said was OEM. The spindle length for the EighthInch 165mm silver crankset is different; 110mm. However, because you claim you have a 70mm shell, if so the only readily available BB is this one from Velo http://store.velo-orange.com/index.php/components/bottom-brackets/grand-cru-threadless-bottom-brackets.html or as I said before, have 2mm (1+1) trimmed from your 70mm shell to make it the 68mm standard size.

There is one other option. Assuming your BB is loose ball and the cups are still in good shape, you can try and find an Italian BB spindle the right size.