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Wheel words: learn the jargon

There is a proliferation of ready-built wheels on the market, but you still get the best value by attaching a hub to a hoop with a bunch of spokes yourself. If you do the weaving and tensioning yourself, you can spend the extra you save on a rim upgrade.

Your first attempt at building a wheel often takes some time, but it is a very satisfying experience. Once you’ve managed your first one, it gets easier every time. Don’t be tempted to start with a second-hand rim and old spokes; it’s much harder to true a secondhand rim, which will probably be dented and buckled, so will be frustrating since you find yourself doing the right thing without any effect.

Lacing, attaching the rim to the hub with all the spokes in the right place, comes first. This is easier than it looks. Next comes truing up the wheel so that it is round, flat and centred. This looks easier than it is and requires a fair bit of patience and care.

Front wheels are easier to start with than back ones. Back wheels have the cassette fixed on one side, which means the rim doesn’t sit centrally to the hub. Therefore, the spokes on the cassette side have to be tighter than those on the other side. So begin your wheelbuilding career with a front wheel if you can to ease yourself into it.

Disc brakes often come with recommended spoking patterns. This is because braking applies force to only one side of the wheel, so it’s important that the spokes stressed by braking are those that best support the braking force. The lacing pattern given here works best for disc brake bikes and fine for the rest, so use it for everything.

Crossing patterns

Most wheels are built ’threecross’ (3x). To see what this means, look at a wheel and follow a spoke from the hub to the rim. The spoke passes either under or over others on its way. If it crosses three other spokes, it’s a standard three-cross wheel. The other common lacing pattern is ’radial’, where the spokes go directly from hub to rim without crossing any others. It is also known as a zero-cross (0x) pattern.

Radial spoking is used almost exclusively for front wheels. A crossed pattern is more suitable for the back wheel; you’re using the pedals to force the rear hub to turn. The spokes transfer this rotation to the rim and tyre. A crossed pattern means that the spokes leave the flange at an angle, which reduces the stress on both flange and spokes.

For both radial and crossed patterns, alternate spokes are connected to opposite flanges. This enables you to adjust the position of each section of the rim, moving it to the right by tightening spokes that connect to the right flange or loosening spokes that connect to the left flange, and moving it to the left by tightening left spokes or loosening right ones.

In crossed patterns, the spokes divide into pulling spokes and pushing spokes. The pulling spokes get tighter when you pedal and pull the hub around, dragging the rim behind them. The pushing spokes provide a counterbalancing force, thereby keeping the wheel in its strong, round shape.

When you’re braking, the opposite happens – the pushing spokes suddenly have to do all the work, with the pulling spokes supporting them.

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Three-cross is the standard pattern

Spoke length

Whether you’re building a new wheel or replacing a broken spoke, you need to choose the correct spoke. The length needs to be exactly right – a spoke that’s more than 2mm (1⁄8 inch) too long or too short will not fit. Minor differences in flange size (the wider part on either side of the hub, with holes through which to thread the spokes) and rim profile will affect the spoke length.

When replacing a broken spoke, check the length by measuring another on the same side of the same wheel. Spokes are measured from the very end of the threaded end to the inside of the elbow of the head end. When measuring a spoke that’s laced into a wheel, you have to take the rim tape off and look into the rim from outside to estimate how much of the spoke is inside the rim.

Spokes that are too long will protrude up inside the rim, where they can puncture the tube. You can file the ends off, so that they’re flush with the top of the nipple, but that’s still not good enough – only the end of the nipple is threaded, so if the spoke is too long, the nipple will have to cut its own thread on the unthreaded section of the spoke. This usually just damages the nipple thread, which then won’t hold spoke tension securely.

Spokes must be long enough that they’re threaded most of the way onto the nipple – if the nipple is only hanging onto the spoke by the last few threads, it will pull through as soon as the spoke is stressed.

When you build a new wheel, you start from scratch. You can work out the correct length using three-dimensional trigonometry, but it’s hard maths. It’s easier to ask your bike shop to look it up for you – shops have tables of common hub and rim combinations, or computerized spoke-length calculating programmes. Choose a quiet time, not a busy Saturday in July. The shops are most likely to help if you buy the spokes at the same time. In order to work out the correct length, the shop needs to know the hub model, rim model, number of spokes and crossing pattern, so either take along the components you’re using, or buy them at the same time.

If you’re building a wheel, buy a couple of extra spokes, so that you have spares later. Don’t forget to pick up nipples at the same time – they don’t automatically come with spokes.

Spokes come in two types: ’rustless’ – meaning they are cheap – or ’stainless’. Always build with stainless. (The savings kept from using rustless will just be spent on more spokes sooner.) Good makes include DT and Sapim.

“You can work out the correct length using three-dimensional trigonometry, but it’s hard maths”

Spoke gauge

Spokes are usually either plain gauge (the same 2mm diameter all the way along) or double-butted (2mm at the ends where they normally break, and 1.8mm in the middle to save weight). Although spokes aren’t a heavy component, saving weight here is particularly significant – wheels spin around their own axles, so weight saved here makes a big difference in how easily the bike accelerates. For heavier riders, plain-gauge spokes are less stretchy, so they help keep the wheel in shape when you bounce up and down on it.

The holes in the hub flanges are only just big enough for the spokes to fit through. If the fit is very tight, the spokes are more awkward to fit, but the wheel will stay true longer. Baggy hub holes allow the spokes to shift about, wearing the holes and releasing spoke tension. The width of the flange is also important. Once again, there’s a compromise between ease of assembly and wheel longevity – if the hub flange is only slightly narrower than the elbow of the spoke, it will be tricky to ease the bend in the spoke through the hole. However the whole width of the spoke elbow will be supported by the inside of the hub hole, reducing the chance of spoke breakage. Some spokes are a smaller diameter at the threaded end. This does save a little weight, but means that you must use special 1.8mm nipples; while normal 2mm nipples will fit, they will work loose, usually over the first few miles that you use the nipples. Since a spoke gauge does vary from manufacturer to manufacturer, it makes sense to use the same make of nipple and spoke – even if they are supposed to be the same size, wheels built from mix-and–match components don’t stay true as long.

Number of holes

Mountain bike wheels have mostly settled at 32 holes at the moment. The norm used to be 36, but as rims have become stronger, it’s been possible to save weight by losing some spokes. Today, 28-spoke wheels are becoming more common, while 36 holes is still a good idea for heavier riders, or for those prone to trashing lots of wheels. The movement in expensive wheels is toward fewer spokes, but these are harder to build because, as you reduce the number of spokes, the tension in each becomes greater and the precision balance between the tension in each spoke becomes critical. If you’ve not built one before, I recommend getting good at 32- and 36-hole wheels before moving onto the fancy stuff! Road bike rims can have as few as 16 holes on the front and 20 on the rear.

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Rims with double eyelets stay true longer

Eyelets

Rims are made of aluminium, which is light but relatively soft. Good-quality rims have an eyelet pressed into the rim at every spoke hole. These spread the pressure from the tension in the spoke over a wider area of the rim and provide a smoother surface for the underside of the nipple to turn on. Single eyelets (A) sit on the inner surface of box-section rims. Double eyelets (B) are shaped to spread the pressure over both inner and outer surfaces, making the rim stronger but adding a bit of weight.

Lefts and rights

Once only rear wheels had awkward right and left sides, but the advent of disc wheels has sent fronts that way too. The lacing pattern is important because disc brakes are much more powerful than rim brakes. The spokes need to be arranged so that the strongest are lined up to resist the braking force. It’s fine to build non-disc rims in the same way.

When you’re building the wheels, there are lots of right and left directions. Discs are always attached on the left of the hub, cassettes on the right. Non-disc front hubs are the same both ways, but it’s traditional to build them so that if you were sitting on the bike and looked down at the label on the hub, it would be the right way up. Rim labels are usually laced so that they can be read from the right-hand side. Again this doesn’t really matter but it’s a nice touch.

Off-centre rims

There are several different makes of off-centre rims, including Bontrager and Ritchey. Take care when building them – they are confusing. The spoke holes are not central but are set off to one side. Build front disc wheels so that the overhang is biggest on the left; for rear wheels the overhang should be on the right. The overhang compensates for the dish that the wheel is forced to take on because of the extra stuff on the hub – either the cassette or the disc mounting. Reducing this dish makes a stronger wheel. There will always be an arrow on the rim to help you get the right direction.

Deep-section rims

Deep-section rims are good for heavier riders because they keep their shape well, but they can be awkward to build. Good-quality rims are made of a shaped tube, bent around into a circle.

With deep-section rims, it’s easy to drop the nipple into the tube by mistake, instead of in one side and out the other. Once they’re in there, you have to get them out, otherwise the nipple will roll around inside the rim, forever rattling. Sometimes the nipple will come out if you can shake it around until it’s near the valve hole, otherwise you have to tease it out by poking it through of one of the holes with a spoke.

If the rim you’re using is deep, screw the top of each nipple a couple of turns onto an extra spoke, and use that to insert the nipple through the rim hole. Unscrew the extra spoke, then screw the nipple onto the laced spoke. If you build lots of deep-section wheels, you can get a special little deep-section rim nipple screwdriver that grips the head of the nipple so you can pass it safely through the rim. (It’s one of those special tools that seems extravagant to everybody except the person who has to use it . . .)

Nearing the end of the build, you have to bend spokes to manoeuvre them around those already fitted. This is fine, but ensure they don’t get kinked. A gentle bend over most of the length of the spoke is far better than a sharp kink. You’ll always need to bend the spokes slightly when lacing them onto the rim, but building with deep-section rims means fitting shorter spokes into a smaller space, so the bend must be tighter.

Disc wheels

Disc wheels are no more complex to build than non-disc wheels. The flanges are usually bigger, which makes it easier to lace them, but the front wheel must be slightly dished to allow space on the left-hand side for the rotor. The amount of dishing is minor, though, so the tension on each side of the wheel remains fairly even.

Source : BIKE MAINTENANCE TIPS, TRICKS & TECHNIQUES
See also bike maintenance tips, tricks and techniques “What makes spokes break?”