Bicycle Mechanics - Need help with spoke lengths

About to attempt my first wheel build. Think I'm generally comfortable with the tools and procedures. I've used Damon Rinard's Spocalc spreadsheet and Roger Musson's Wheelpro web page to calculate spoke lengths, but I'd like someone to check my work before I start ordering parts...

Planning to build a set of wheels for light (~15lbs of gear) to moderate (~20-30lbs of gear) loaded touring. Frame is capable of supporting either cantilever or disc brakes and I've found a fantastic price on Shimano XTR 975 hubs. Planning to use Velocity Synergy Offset rims, both front and rear. Spokes will be either DT Swiss Competition (2.0/1.8mm double-butted) or Wheelsmith Double Butted (2.0/1.7mm), laced 3-cross. I'll probably go with brass nipples all around.

Here's my data (w/links to the source):

Velocity Synergy OC Rims (http://www.velocityusa.com/default.asp?contentID=591): 604mm ERD, 4.0mm offset

Shimano HB-M975 Front Hub (http://bike.shimano.com/publish/content/global_cycle/en/us/index/products/mountain/xtr/product.-code-HB-M975.-type-.html):
Center to Left Flange: 24.9
Center to Right Flange: 35.7
Left Flange Diameter: 44.0
Right Flange Diameter: 40.0
Spoke Hole Diameter: 2.6 (according to pvd (http://www.pvdwiki.com/index.php?title=Spoke_Length_Notes#Shimano_XTR))

Shimano FH-M975 Rear Hub (http://bike.shimano.com/publish/content/global_cycle/en/us/index/products/mountain/xtr/product.-code-FH-M975.-type-fh_mountain.html):
Center to Left Flange: 35.3
Center to Right Flange: 22.1
Left Flange Diameter: 44.0
Right Flange Diameter: 45.0
Spoke Hole Diameter: 2.6

For the front wheel, Spocalc says the spokes are 294.4 and 295.3.
WheelPro says the spokes are 294.2 and 295.2.

For the rear wheel, Spocalc says the spokes are 294.6 and 294.0.
WheelPro says the spokes are 294.5 and 293.8.

Sheldon (http://sheldonbrown.com/wheelbuild.html#length) suggests rounding legths upward to the next higher size, but I've read more than a few posts that suggest rounding down to the next smaller size in an attempt to avoid ending up with spokes that are too long. What length spokes should I buy? 294 and 295mm for the front? 294 and 293mm for the rear? 294mm for everything?

unless you're going to get the spokes custom cut, you'll have to do some rounding. i have the phil wood spoke cutting/ thread rolling machine, and it's difficult to be accurate beyond the decimal point. that being said, in my experience, you want to round down, but not too much that it'll make your wheel build difficult. keep in mind that the synergy's are double walled rims, so you have a little bit of leeway when it comes to spokes protruding from the nipples.
before you choose your spokes, make sure they fit your hubs nicely. it's my understanding that the elbows of DT spokes have been lengthened specifically to fit xtr hub flanges.
definatly go with brass nipples. aluminum ones just ask to be rounded unless you have a 4 sided spoke wrench.
with all that said, if i had to build your wheels, i would cut 32 294 and 32 295 spokes and build the wheels with those lengths. (by the way, i just checked qbp and both wheelsmith and dt spokes are only available in whole sizes)

in the end, as long as your spokes are close to the length needed, and all the spokes on the same side of the wheel are the same length, you'll be fine.
take it easy, take it slow, make small adjustments at a time. if you can, bring the wheels into your LBS to have them check the final spoke tension. if you are going to go touring on these wheels, you want them to be good.
good luck, keep us posted

before you choose your spokes, make sure they fit your hubs nicely. it's my understanding that the elbows of DT spokes have been lengthened specifically to fit xtr hub flanges.

Hadn't heard that. Good to know!


with all that said, if i had to build your wheels, i would cut 32 294 and 32 295 spokes and build the wheels with those lengths. (by the way, i just checked qbp and both wheelsmith and dt spokes are only available in whole sizes)

Thirty-two 295mm spokes? Is that a typo? If we round down, I'd think that you'd want 48 294mm spokes and only 16 295mm spokes...

BTW, is there any point to ordering a few extra spokes for the first wheel build? I can't really imagine any way to mangle a spoke to the point of being unusable, but I'm wondering if it's possible? I'll probably order a couple of extras just to have some spares, and maybe a few extra nipples too, but I'm wondering if there's any reason to do more than that...

There's almost always a little slop possible in spoke length, so don't overthink it. A couple mm isn't going to make a difference in most cases.

Always order several spare spokes so you have them if you break one!

Always order several spare spokes so you have them if you break one!

I was planning to order a couple of spares. Didn't know if I needed to order, say, a dozen spares for my first build attempt or if 1-2 would be enough :D

Seems like it would be difficult to ruin spokes during the build. I guess if you do a bad job building the wheel you could end up breaking them during the first few rides, though. So maybe a few additional replacements are probably a good idea.