Buying spokes
 

How accurate does the spoke you buy have to match the spoke you need?

Say, I need 305.4 (left) and 304.2 (right), can I just get 306 and it fit ok?

Also, 276.1, 276.8 for the front, do I buy 277 or 278?

Round down, not up. You may run out of threads to tighten with with an overly-long spoke. Rounding to the nearest even (or odd) number should be fine too, so you will be fine with 304's and 276's (although by rounding down by 1.5m, you may get some threads showing past the nipple, which is just an aesthetic issue.

I just read Sheldon Brown's wheel building. He said round up to the nearest available size. Not sure if I agree with that, I understand easily how if the spoke is a bit too long, there's no more thread to tighten on.

This just occurred to me - in a higher tensioned lacing you'd need slightly (sub .5mm) shorter spoke, but wouldn't the crossing pattern cause exaggerated bends at the crossings?

I'm thinking that you lose a tiny amount of linear length with each crossing, and this might be exaggerated at a higher tension.

I'm completely speculating, so if someone knows this to be wrong, please let me know.

It's amazing how often this question comes up.

Always round down, especially important for driveside rear spokes because the higher tension required to dish the wheel can cause you will run out of threads before reaching full tension. Double butted or skinny spokes often stretch magnifying the problem. I buy my driveside rear spokes at least 1 mm shorter than calculated.

Al

Since you buy your driveside spokes at least 1mm shorter than calculated. What about other spokes (non-driveside and front wheel)?

As others said, round down. I once ordered spokes ~2.5mm too short (by mistake), and they turned out long enough.

Others may know more, though.

I'm finding it difficult to source 304mm black spokes, I guessing 302mm will work fine?
What are some of the online sources people buy spokes from?