SPOKE LENGTH TOLERANCE
After you have determined the spoke length you will need for your wheel, you will obviously have to get spokes close to those lengths. Some shops only stock spokes in even lengths, and some spokes are only made in even lengths. Whether or not you can get spokes in single millimeter (mm) increments or only even mm lengths, you need to convert your calculated length to the proper length of the spokes available to you.
As was briefly mentioned on the Home page, you also need to compensate the spoke length according to the type of wheel, where on the wheel, and the lacing pattern the spoke is going to be used for. You will need to be aware of any offset or stagger of the spoke holes on the rim you are using as well in order to make accurate compensations. Rim stagger and offset adjustments are discussed on the MEASURE page. Spokes that are a little too short are better than ones that are a little too long. So if you compensate a little too much there should be no problem. If, however, the spokes end up being too long, you could try to still use them by adding a crossing, the FIXES FOR SOME PROBLEMS chapter discusses this problem.
Spokes do stretch when you are building a wheel from the tension, and the thinner they are (including the middle of butted spokes) the more they stretch. In multi-speed rear wheels (those with freehubs or freewheels), the drive side spokes stretch the most. Front wheel spoke stretch is less than the drive side spokes, but more than non drive side spokes. Single speed and internally geared hub rear wheel spokes have about the same stretch as front wheel spokes. Any spoked wheel with either no dish offset or only a slight amount (like front disc brake wheels) should go with the compensation for front wheels. See the GENERAL WHEEL LACING for more information about dish offset.
The following paragraphs are organized in the logical order to figure out the compensations to calculate the spoke length. The best way to work these compensations into the formula is to subtract the compensation from the RRSP value. These compensations should work fine for 28, 32, and 36 spoke wheels. For 48 spoke wheels compensate 1mm less, for less than 28 spokes compensate 1mm more.
For drive side spokes start by subtracting 1mm as a general compensation. For 14 gauge spokes, if you are using a 3-cross pattern subtract 1mm more, if you are using a 4-cross pattern subtract 2mm more. With 14 gauge spokes radial or 2-cross lacing's do not need another compensation. If you are using 14-15-14 butted spokes subtract 1mm more for a radial or 2-cross pattern, 2mm more for a 3-cross pattern and 3mm more for a 4-cross pattern. I do not suggest using 15 gauge straight spokes, or a butted spoke smaller than 14-15-14 for the drive side.
For non drive side spokes that are either 14 gauge, 15 gauge, or 14-15-14 butted, you can use the same cross pattern compensations listed above for 14 gauge spokes but without the general 1mm compensation. For 15-16-15 butted spokes, or butted spokes with a middle section smaller than 16 gauge, use the compensation values for the 14-15-14 butted spokes above without the general compensation.
For front or other low dish offset wheels subtract 1mm from the RRSP value as a general compensation. If you are using a 4-cross pattern and 14 gauge spokes subtract another 1mm. If you are using 14-15-14 butted spokes or 15 gauge straight spokes subtract another 1mm for all lacing's except 4-cross, then subtract another 2mm. If you are using 15-16-15 butted spokes, or butted spokes with a smaller middle diameter than 16 gauge, subtract 2mm for all lacing's except 3mm for a 4-cross.
If you are making wheels for a wheelchair or a trailer, or any other wheel that has dish offset greater than 10mm, use the compensations for rear wheels, both drive and non drive, discussed above.
After calculating out the length of the spokes, you will most likely have numbers that are not round, like 265.89 or 260.03. You will need to round out the number to get a usable value. I have found that due to the nature of spoked wheels rounding the numbers out by eliminating the fractional value works best. For example, if you calculate a spoke length of 267.123, get a 267, if you calculate out a length of 261.895, get a 261.
Nipples and spokes have enough threads on them that spokes will work fine if they are a little too short. The only real problem with spokes being too short is that a nipple-driver screwdriver would not work to get the spokes started when you started building the wheel. The first spokes that you tightened up would work, but once you were about half way around the wheel, the screwdriver would tighten the spokes to their limit before it reaches it's spin-off point. The other problem with spokes that are a little too short is that the threads might show a little, but if you don't care about this, the wheel will work just fine and be as reliable as if the spokes were longer. Spokes that are a little too short will also allow you to finish the wheel, unlike spokes that are a little too long, so it's better to compensate a little too much than not enough.
If your spokes are too short and you will have to get the wheel started using only a nipple wrench, try this. About the easiest way for starting all of the spokes evenly in a case like this is to take an extra unneeded spoke (maybe an old one), cut it so it's about two inches long off the threaded end, and wrap a piece of tape around the spoke about 3mm from the end that's threaded. Make sure to use enough tape that it will stop the spoke from threading into the nipples for the whole build, 5 or 6 layers worth. Thread this spoke into the nipple from the 'inside' until the tape touches the nipple and keeps it from screwing in more. After starting a spoke, tighten the nipple to the point where the wheel's spoke touches the taped spoke, look for the nipple to start backing out as an indicator of the spokes touching. If you do this properly you will have a starting point where all of the spokes are evenly seated in their nipples around the wheel. Finish building the wheel like normal.
