Bicycle Mechanics - Spoke Length Calculators and Selecting Spokes

Good morning everyone,

Im buidling up a set of wheels (first time).
I have a spoke tension gauge, wheel truing stand and spoke wrench to do the job.

I have done all the measurements and run them thru a couple spoke length calculators.
They say "..these are maxium lengths..."

How accurate do I need to be when buying the spokes since not all sizes are available?

If I need
299.9mm front
296mm left and 295mm sprocket rear

Can I buy a bag of 299mm and 295mm spokes?

How far can I go from the original measurement? 1mm down, 2mm down? 3mm?? or up?

You can go 1mm down for sure. Maybe even 2mm. But never use longer spokes!

You can go 1mm down for sure. Maybe even 2mm. But never use longer spokes!
^^ +1

I'd do as you suggest; 299s and 295s

The problem with going longer is that you run the risk of the nipples bottoming out of spoke threads before achieving adequate tension.

^^ +1

I'd do as you suggest; 299s and 295s

The problem with going longer is that you run the risk of the nipples bottoming out of spoke threads before achieving adequate tension.

I agree almost entirely. The only exception I've found is when shops use a Phil Wood machine to manually cut spokes for me. Maybe it's the dude, maybe the machine, but I've done this at 2 shops and both times I left with >= .5mm too short. Neither incident was a show stopper, but rounding up 1mm is a better bet for me in these cases.

Don't to hijack the thread, but on the subject of manually cut spokes - is it just me or are the manufactured ones a lot smoother? I just laced up a wheel with DT comp DB spokes out of a box and they threaded effortlessly into the nipples.

When using double butted spokes I round down an extra mm on the driveside rear. But it also depends on how you calulate the lengths. The DT Swiss calculator automatically rounds down an additional mm for the DS rear if Revolution spokes (2.0-1.5-2.0) are used.

Al