02-22-2013, 01:28 PM
I bought a compact crank (48-36 Velo Orange) for an old 1980 Trek. I found that the old bottom bracket spindle (122mm) was too long. The recommended bottom bracket length for the new compact crank was 110 mm. I bought and installed a sealed 110 x 68 bottom bracket. I thought I would be out pedaling within an hour. However, with the chain on the small chainring and the smallest rear cog (12 tooth) of a 6 speed freewheel, the chain is rubbing and catching on the large chainring. I need to move the crank out, or slightly to the right. I tried to fix the problem by installing two spacers on right side of the bottom bracket, but the chain still rubs. I doubt that installing more spacers is advisable. I can see that my chain angle is too extreme and a longer bottom bracket is needed. I'm resigned to buying a second bottom bracket, but at $30 a pop, I don't want to buy the wrong one. I'm thinking a 113mm or 115mm should work, but I'm guessing. Can someone tell me a simple way of measuring the chain angle or chainrings that will give me the right length for a new bottom bracket? Thanks.