Gerryattrick

I am planning on building up a rear disk brake wheel using a Mavic Open Sport rim and a Shimano M475 hub. As far as I can work out I need 289.9 & 291.1 mm spokes.

I understand the benefits of using the correct spokes, but I have been offered a complete set of 292 mm spokes and nipples by a friend Given that these are double wall rims so there will be little or no chance of the rim protruding past the inner wall, will it be OK and safe to use these spokes, which are 2mm & 1mm longer respt.

I have the hub and rim already so I am tempted to try this as it will give me a free rear wheel. Am I being too miserly?

Andrew R Stewart 

A mm or 2 too long is usually ok depending on where the original length was meant to end up at WRT the nipple. But 3mm and expect a lot of spoke poke through and or nipple bottoming out on the threaded portion of the spoke. As you're located at the side of the road (dropped by the peloton) you likely don't have a spoke cutter available. But if you should be able to ride past a shop you might ask if they can cut 3mm off the drive side spokes. Expect to pay for their time and tooling.

I find that trying to save $ with spokes is usually a bad choice or more expensive some way then hoped for. Andy.

Drew Eckhardt 

A 12mm DT nipple has 8mm of thread, and DT spoke 9.5mm. You run out of threads once 1.5mm of spoke is protruding which is 2.5mm above the slot bottom. Other makers' products are similar.

You get about 0.5mm of stretch from a 2.0/1.8mm spoke at 105kgf.

Your drive-side spokes will be about 2.5mm too long and are likely to bottom.

On the NDS they'll be OK if the calculator was aiming for the slot bottom and the rims are in spec. If the calculator aimed for the nipple top, or your rim is 2mm short of the published ERD you may have problems.

Note the "ifs." You really need to measure your rims using your spokes and your nipples. Insert a pair of spokes in opposite holes, thread the nipples on to your target depth (usually the slot bottom), measure across the elbows with calipers, and add twice the spoke length to arrive at ERD. Repeat 90 degrees away. If measurements differ measure at the remaining 45 degree positions and average.

If necessary you can drill nipples so they thread on farther, or use spoke washers to add ~1.5mm to the ERD.

nfmisso

It is VERY VERY difficult to cut off LESS than the whole threaded portion of the spoke and re-thread. This is because it is difficult (sometimes impossible depending on the tooling) to extend rolled threads.

NOTE: spokes have rolled, not cut threads. Rolling threads moves material about, it does not remove material.

Personally, I recommend purchasing new drive side spokes.

Bill Kapaun

You didn't specify what spokes you were offered.
IF simple straight gauge spokes, I'd be less inclined to experiment and just buy DB spokes instead.
IF these are DB spokes, maybe just use 1/2 of them?

Gerryattrick

Thanks for the very helpful answers so far. I can see it is not as straightforward as I hoped it might be. Just tried screwing some of the nipples fully on and the spokes do stop just 1-2mm past the bottom of the screw slot so I wouldn't want to risk it for the shorter side spokes in particular, as I might not be able to get the tension right.

Some interesting ideas such as drilling the end of the nipples or using spoke hole washers.

Straight gauge spokes, so I now have to decide whether to get past my usual meanness, rather than compromise on the build.

I have built a couple of wheels in the past, but they were front wheels, so no dishing, and I had the correct length spokes.

cyccommute 

I would agree that cutting the thread off is not the way to go but it's not that difficult to extend the threads. Hozan makes a threading tool which works quite well, although it is expensive and not cost effective for just a few spokes.

On the other hand, the spokes that Gerryatrick have been offered are not 3mm too long. A 289.9mm spoke is a 290mm spoke. In fact, find a 289mm or a 291mm spoke is difficult in my experience. Most people stock even length so he would likely use a 290mm and a 292mm anyway.

FastJake

The way I calculate and build wheels always has me round up to the next size. Yellow Jersey bike shop only carries even sizes so I'd buy 290 for the drive side and 292 for the non-drive side. So, your free spokes should be the right length for half the wheel.

If cheapness is the primary goal I'd get some washers for the drive-side and call it a day. Depending how you measured you might even be able to use the spokes without washers.

Dan Burkhart 

I routinely shorten spokes by as little as 2mm with my Morizumi machine. It picks up the original thread every time when the proper technique is applied.
I have never used a Phil Wood threader, but some say you can extend threads with it, and others say forget it, you will just mash down on the old threads.

Andrew R Stewart 

Said by someone who hasn't used either a Phil or a Morizumi cutter. Or it sure sound like this is the case. As Dan said with his Morizumi and I have experienced with my Phil, it is very easy to cut as little as 2-3mm off a spoke and pick up the remaining threads as you ROLL the extra new threads. We do this often at work (where my Phil resides).

So, Nigel, have you used one of these spoke cutters? If so then I take back my assumption about your experience and feel sorry that you haven't gotten the hang of them yet. Andy. (Who already mentioned his preference to not fudge with spokes as a way to save $)

79pmooney

I will second the advice above from personal experience. You do not want to bottom out the threads of the drive side spokes. They get tough to turn anyway. You may not even know you have bottomed out for a while. And you might have that happen with a wheel that is "almost there". You go a little harder. The nipple distorts. Not a whole lot of fun.

Have enough washers to go two per drive side it you have to. Unlikely, but two washers would be far better that bottomed threads. (And purchasing two per drive side is just buying enough for a whole wheel; what I am sure the shop would prefer to sell you anyway. And if you go to Ace Hardware, they are cheap.)

BEn

Dan Burkhart 

So, one more in "can" camp with a Phil Wood. Good to know, although I expect my machine is a lifetime investment, and no reason to change.
One other thing that my machine can do that I have been told is a "fuggedabouditt" with a Phil Wood is to shorten and thread bladed spokes.

Plimogz

I recall building a good wheel with same length spokes all 'round -- coincidentally, I believe that they were 292mm as well, oddly enough. The optimal lengths spit out by the spoke calculator were similar to yours; in other words, 292 was the nearest even integer above the longer side, but 2mm shorter would have been preferable on the other side. If memory serves, this was with straight gauge wheelsmith spokes and nipples, and the only downside was the drive side spokes poking up through their nipples slightly above flush.

That said, I feel like I got slightly lucky with that build, and if I were doing it over again, I would just buy the 290mm spokes I needed and be confident that everything was going to be in its right place when I was done.

***

On a related note, if that mystery location of yours is actually Montreal, consider dropping me a PM: I have more 290mm straight gauge laying around than I know what to do with -- now that I have moved on to basically only building with double butted...

FBinNY 

Rather than trying to roll another 1-3mm of threads onto a spoke, I would remove 2-3mm from the nipple. This is fairly easy to do, though odds are you'll sacrifice your first few nipples while you dial in the touch.

You'll need a 2mm drill bit and either a Dremel or power drill which you can clamp into a vise. Then you hand feed the h=nipples onto the spinning drill. You can control the depth by drilling a few nipples clear through and stacking them onto the bit, so you can only drill to a set depth. If you have good finger strength, and decent touch so you feed slowly, you can do this hand holding the nipples. Otherwise you can use a screwdriver to keep the nipple from turning as you guide it to start it with your fingers.

I've done this numerous times, and can do something like 10 or more nipples per minute.

Of course, you can also shop for nipples with less thread so they allow more overrun distance. Wheelsmith nipples used to be that way, but I don't know if they still are.

Classtime 

From my limited experience (10-11 wheels), a little long is easier than a little short. If they are a little short, then you have to go around and back off the nipples when they can't all be tightened those first turns with the nipple driver. Not a big deal but annoying. Btw, I use Roger Musson's e-book.