Someone give me assurance (or correction) on this please!
I'm converting a colnago frame with 126mm rear spacing to a fixed gear. I have campy record track hubs and i've just ordered a longer axle to deal with the larger spacing. I have a campy chorus BB and i am considering getting a campy pista crankset off ebay at some point.
So at this point i am about to get some spacers for the rear axle to deal with the spacing correction. If i put a 3mm spacer on each side should that give me a reasonable chainline? Should i just wait and see how it needs to be spaced once i get the crankset? help!
Dropout width is irrelevant. Your track hub will retain the same chainline regardless of whether you space out the axle evenly or cold set your frame to 120mm. If you want to run a Pista crankset you need to get the right length BB to deal with the chainline.
I won't be cold setting the frame, I would like to keep the option of running gears someday. I was under the impression that i could space the axle to move the chainline to one side or the other.
Sure, you can do that, but you'll have to re-dish the wheel. If I were you I would deal with the chainline issue up front whether you're planning on running pista or road cranks and keep the nice Campy track hub axle symetrical.
If you still have a set of road cranks mounted measure the distance between the inner chainring and the center of the seat tube. If it's very close to 42mm you should be set. Use that inner chainring or something a little bigger if you wish and get rid of the outer ring. I don't think you'll get a decent chainline using the outer crank spider unless you use a considerably shorter BB.
You're actually in a great position because you have a lot of options to get the chainline right. Strongest way to go is to keep that rear axle equally spaced on either side and run the wheel with a symmetrical dish. They make bottom brackets with different spindle lengths, if you're lucky, and you have a three piece bottom bracket, sometimes you can even flip the spindle around to get the correct chainline (assuming it's asymmetrical). If you have a track hub, and add equal spacing to either side of the axle, thus keeping the hub in the same position relative to the rim. That puts your rear cog in the right place to line up with a pista crank. To fine tune the chainline, use chainring spacers. (Unless you're opposed to them, on the grounds of aesthetics, in which case you can safely take a minimal strength hit on that rear wheel and play with the dish and axle spacers.)
Ok well i will keep the rear axle spaced evenly. The campy bb is 102mm.. and from what i can gather through ebay.. track spindles are 111? So i am assuming that a pista crankset would not line up without replacing the bb... right? Ahh.. i'm trying to work this all out in my head without the parts in front of me, sorry if your having to walk me through this
Only way to know if it will be right is to get it all set up and measure, then correct. No matter what the stats say, there's always some fudge factor. You can get the wheel redished pretty close and then just tweak the space and dish to finalize.