Lacing the Wheel
If you're reading this page, you're probably not an expert. So you'll just botch it up. And the equipment required to do it right costs enough that you won't make your money back, even after building several wheels. So, right now, reconsider whether you want to do this.
Dishing: Rebuilding a wheel requires a dishing tool. This is a gauge that measures the amount of offset of the rim relative to the hub. (Look at your back wheel. Although the rim is centered within the dropouts, it's NOT centered over the hub -- the spokes are more angled on one side than another, to allow room for the cogs. This offset is referred to as "dishing." Front wheels with disk brakes will also have dishing.)
Truing: You will also need a truing stand to determine both concentric (roundness) and lateral (side-to-side) truing. So even with the cheapest dishing gauge and truing stand, you're looking at more money in TOOLS than you'd spend having a pro build the wheel four times! And how tight do you make the spokes? You might need a tension gauge, too. (For minor truing, see our section on truing the rim.)
Gauge: Spoke thickness is measured as "gauge," with higher numbers meaning thinner spokes. Many mountain bikes use a 15-gauge spoke. Thinner spokes (16) are lighter for racing, but tend to stretch when you ride hard. We don't recommend them for real mountain bikers. If you're a hard-core jumper or a violent downhiller with disc brakes, we suggest 14 gauge straight spokes. Disc brakes require beefier spokes than V-brakes, because the braking force is transmitted through the spokes from hub to rim.
Butting: If the spoke is fatter at the end than in the middle, it's called a "butted spoke." If both ends are fat, it's "double-butted." For example, a 15 double-butted has a 15-gauge shaft with both ends thickened to 14 gauge. If you need spokes that are stronger at the hub, but want them light, use a butted spoke. If you need strength down the entire length of the spoke (to prevent stretching), use a thicker straight spoke.
Lacing: The spokes can be placed into the rim in different arrangements, referred to as a lacing pattern. "Radially laced" means the spokes go straight from the hub to the rim. This is for roadies. Don't even think of radial lacing for a mountain bike. "Three-cross" lacing is the pattern for most mountain bikes. As a spoke leaves the hub, it will go past two other spokes, then cross over to the other side of a third spoke before inserting into the rim. "Four-cross" is for hard-core downhill and jumps. The wheel is a bit stronger, but the additional spoke length adds to the bike's weight.