Building a Fixie #3 - bicycle part sizing issues

July 26, 2007 at 10:52 AM | categories: Bicycle | View Comments |

Bicycle project continues. Many of my bicycle parts have arrived - frame, bottom bracket, moustache bars, SPD pedals and shoes. 700C wheelset with flipflop hub should arrive today. Last night I went to American Cyclery on my way home from work and purchased a Sugino RD crankset (165mm), tires, tubes, a cheap seat post (didn't know if it would fit), a chain (shop had many different colours, i went with normal), a pedal wrench (big sturdy thing), a bottom bracket tool (with Italian threads, I figure I'll need to do frequent tightening) and some heavy duty lubricant.

With all this stuff, I was able to begin my process of discovering all the mis-matched and incompatible parts I had actually bought. Since I began this project with pretty much zero knowledge of building a bicycle, I fully expected I would make mistakes along the way in terms of buying parts. I figure if I have to buy another of some part to correct an error, its just an additional educational expense. The thing I was most worried about was the bottom bracket and crankset. Having an Italian threaded frame, it is a little more difficult to find bottom brackets. I semi-blindly purchased a fancy Truvativ GXP Team cups bottom bracket from eBay, in the hope that it would fit my crankset (which I had yet to purchase). It turns out that the Sugino RD crankset requires a square taper bottom bracket, 103-107mm width shell. I don't actually know exactly what kind of crankset the Truvativ BB takes, but its clearly not mine. In any case, I need to get a new BB. Sugino make their own square taper cartridge BB in a 103mm size which I would be happy to purchase except for the fact that its not available in Italian threading. After some searching, I found that sell the Shimano UN53 in a 70x107 sizing, which should hopefully both fit in my frame's BB and support the Sugino RD crankset. At ~$23 for the BB, this lesson seems to come at a pretty good price!

The second sizing issue I encountered was in the seat post. Having looked at Sheldon Brown's entry on Italian bicycles, I figured the seat post diameter on my bicycle would be relatively standard. I asked the shop for a 'standard' seat post (although the cheapest one) and they gave me what I assume was 27.2mm. It is slightly too large. I also tried the seat post from my current Trek road bike, which also was too large - again I presume it was 27.2mm. I intend to try to exchange it for a 27.0mm, which should hopefully fit. Another thing to note is that saddles are bloody expensive. Cheapest I saw in American Cyclery was $50 (in an ugly colour), and many were well over $100. I figure I will cannibalise the seat from my Trek for the fixie, at least for starters.

Niall O'Higgins is an author and software developer. He wrote the O'Reilly book MongoDB and Python. He also develops Strider Open Source Continuous Deployment and offers full-stack consulting services at

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