Which spokes do i need

The spokes are stresses only under tension and because of their intrinsic rigidity, they hardly change their shape at all. High-quality spokes that have to deal with high stresses often have a smaller cross section of 1. That allows some minimal stretch and helps to better absorb impact. That means, however, some loss in rigidity and therefore in force transfer, which is why these kinds of spokes are more likely to be used for mountain bike sports.

Spokes with a reinforced arc and the same diameter throughout are called single butted spokes , while those with a thinner mid-section are referred to as double butted spokes. These are supposed to help reduce wind resistance — but that only works if they are aligned precisely. We generally distinguish between two spoking types: Radial and tangential.

In radial spoking , the spokes are positioned straight towards the hub, which is a definite plus for rigidity. This type of spoking is recommended only for front wheels with rim brakes , because it is less suitable for absorbing forces from disc brakes or drive forces. Radial spoking can also mean less weight, as radially spoked rims are shorter. In tangential spoking , the spokes are crossed over during mounting.

Here too, we can distinguish between three types:. Two further essential components of a wheel are the rim and the hub. Both differ from one type of sport to the next, but they all basically serve the same purpose. The hub consists of an axle, bearing and hub housing and may also contain a brake or an overrunning clutch. Spokes that are too long can end up protruding way past the nipple. These spokes are likely to rub against the rim strip or rim tape and eventually cause a flat.

This excess thread is a clue that this spoke is too short for this wheel configuration. In the cutaway, we see that both the spoke and nipple have a lot of unused thread, resulting in poor engagement. Looking into this rim we see that the thread of the spoke extends far beyond the nipple. This can be bad news for the tube or tubeless setup.

If done correctly, the measurements and calculations done here will result in spokes that are just fully threaded into the nipples. Having the spoke up into the nipple reinforces it, and helps prevent cracking and failure of the nipple, especially aluminum nipples. Spokes are typically available in 1 millimeter increments, and the proper length is determined by formulas which are based on a series of measurements. These measurements can be fed into online spoke calculators to run the formulas that arrive at a final length.

As you proceed, try to measure accurately. When using a caliper, take measurements to one tenth of a millimeter. This helps prevent measuring errors from compounding along the way. In the end we will round to a whole number for our final spoke length. Although there are online databases for rim and hub dimensions, not all third-party databases are current or accurate. In some cases, you may find it best to take your own measurements. We will walk through how to find each of these measurements.

The first consideration for the rim is simply the number of spoke holes. Count them and make sure it matches your hub. Record it on the worksheet. There are a few ways to measure the diameter of a rim. We are concerned with the diameter as defined by where the end of the spoke sits when it is fully threaded into the nipple. This number is sometimes provided by the rim manufacturer on their website or in the included literature.

However if you have the rim in hand, it is worth measuring this yourself. As we are looking to measure to a point inside the rim, there is no practical way to measure the ERD directly — it will require a few measurements, and then some simple math. This is accomplished with two J-bend spokes with standard slotted nipples, acting as measuring rods. Note that these are not necessarily the spokes or nipples we will use to build the wheel — any identically-sized spokes will do, they only need to be short enough to not meet in the middle.

Determine the length of your measuring spokes with a spoke ruler and record this number. Spokes are typically available in whole millimeter increments. Select a rim hole and engage a spoke through the hole. If you intend to use a rim washer, install it now to factor it in to your measurement. Thread on the nipple to the point where the spoke just comes to the bottom of the slot.

This is where we want the spoke to end on a finished wheel. Find the exact opposite rim hole and repeat the process with the other spoke. Pull both spoke heads inward towards the center to seat the nipples. Using the narrow tips of the caliper jaws, measure from inside to inside of each J-bend. Record this measurement to the nearest tenth of a millimeter. Another aspect of the rim that needs to be accounted for is rim offset, which is a feature of asymmetrical rim designs.

Offset is the distance from the rim center to the spoke holes. The first rim shown has spoke holes drilled straight down the middle. It is a symmetrical design and has no offset. The rim in the center has spoke holes equally staggered left-right-left-right from the center line of the rim. It is also considered symmetrical with no offset. The rim on the right is an asymmetrical design, with the holes offset from the center of the rim. On an asymmetrical design, the wider side of the rim should match the side of the hub with a greater flange inset.

On a rear wheel, the wide side faces the sprocket side. If you're a real stickler, you could insert the outside-measuring blades of the caliper into the spoke holes to take a smaller measurement, and the inside-measuring blades at the top in the picture to do a larger measurement, then take the average.

Subtracting the smaller from the larger measurement and dividing by two would also give you the diameter of the spoke holes -- but that is usually 2. You don't need a caliper. You could cut a C-shaped recess in a piece of cardboard, mark the spoke-hole spacing as shown in the photo at the left, and then measure it with a ruler. A hub flange farther from the centerline requires longer spokes, but only slightly longer with most wheels because the spokes approach the hub at a high angle.

Usually with a front wheel or the left side of rear wheel, you can go with a typical spacing of 35 mm, and with the right side of a rear wheel that has multiple sprockets, 20 mm. The drawing below is of the same hub shown in the previous two photos a SRAM DualDrive hub, a 3-speed with a cassette body for hybrid gearing.

The dimension in red is the OLD overlocknut distance , and the dimensions in blue and green are the flange spacings. They are very near the generic ones already given. With unusual hubs, and especially with a large hub in a small rim, you must measure the flange spacing, or read dimensions from hub specifications. If both flanges are the same distance from the centerline, measure the spacing between the flanges and divide by two.

If the two flanges are different distances from the centerline, measure them independently. Resting the locknut against the edge of a workbench or table makes measurement easier.

An example is shown below, using the same hub. Both ends of the hub are measured. First, let's measure from the right end. The right flange is 50mm to the left of the right locknut , and the left flange is at mm to the left of the right locknut. Next, turning the hub over and measuring the other end, the left flange is 35mm from the left locknut. Calculating now, the overlocknut distance is mm, as in the manufacturer's specification in the drawing above.

Half that is The right flange, at 50mm from the right locknut, is These measurements are not an exact match for the manufacturer's specifications, but are close enough for all practical purposes. Some rims have spoke holes closer to one side than the other, to reduce dishing when the hub has unequal flange spacing.

Then subtract the offset of the spoke holes from the hub flange spacing of the same side as the offset, and add it to the hub flange spacing for the other side. For example, if the left flange of the hub is 35 mm from the centerline, the right flange 20 mm from the centerline and the spoke holes in the rim are offset 3mm to the left, then the effective flange spacing is 32mm on the left and 23mm on the right.

Damon Rinard has another description of hub measurements on this site. Some spoke calculators, including Damon Rinard's Spocalc on this site, perform only the mathematical calculation described earlier in this article. Other spoke calculators account for the stretching and seating of spokes and shrinkage of the rim in a tensioned wheel -- about 1 millimeter of spoke length in a typical wheel.

If the spoke calculator already accounts for tension, then specify spoke length based on where you want the ends of the spokes to reach. Generally, metal rulers with etched markings are highly accurate, and tape measures of reputable brands Stanley, Craftsman etc.

A tape or ruler of plastic, fabric or wood cannot be trusted. Plastic and wood expand and contract with changes in temperature and humidity; fabric also stretches. Spoke length is measured from the inside of the elbow, as shown in the image below, to the threaded end.

When measuring a spoke using a tape measure, a second spoke may be used to hold the elbow of the spoke and the tape measure's tab, as shown. Yes, I know that the number of decimal places exceeds the precision of measurement, but digital calculators give you the extra digits at no extra cost.

Multiplying that number by The ruler and the manufacturer's identified spoke length agree very well. As long as your tools are good, selecting the wrong spokes for a wheel is more likely to result from an outright mistake than from a measurement error.

Though you should always measure carefully, wheel measurement is more forgiving than you might think. Errors in measurement of the rim's diameter result in only half as great an error in spoke length. Deriving the diameter from the circumference improves accuracy further by more than 3 times. The importance of the hub spoke hole circle diameter depends on the spoking pattern.

With a radial spoking pattern, spoke length changes at half the rate of the diameter of the hub flange. With higher cross numbers, the effect on spoke length becomes smaller and smaller. With a spoke cross 4 pattern, the spoke holes are 90 degrees away from those in the rim, and the hub spoke hole circle diameter hardly matters at all. A spoke cross 4 pattern pattern is a good choice when the hub's dimensions aren't known or with flanges of different sizes.

With both wheels spoked this way, a bicycle tourist would need to carry only one length of spare spokes, despite different flange sizes on the front and rear hub, etc. For typical wheels, random errors dominate, but for larger wheels, and particularly, very large wheels such as on antique high-wheeler bicycles, proportional errors -- from the scale of a measuring tape being slightly to large or small, and from spoke stretch under tension -- become important. The ends of the spokes of a fully-tensioned wheel come to somewhere between the bottom and top of the slots in the spoke nipples.

Properly-tensioned spokes stretch by about 0. The range of spoke lengths which avoids these problems is about 3mm. The tolerance has become smaller in recent years, because short spoke nipples and matching short threads are fashionable to reduce aerodynamic drag.

The threads of all four spokes in the image below extend equally far. The leftmost nipple is threaded on until the threads start to bind. The next spoke nipple is threaded on until the end of the spoke is level with the top of the nipple's screwdriver slot, as far as it can go without risk to the inner tube.

The rightmost nipple is threaded on only far enough to conceal the threads of the spoke, risking nipple breakage. Comparing the leftmost spoke with the bare one shows that the internal threads of the nipple extend down about as far as the base of the wrench flats.

I thank Roger Musson for permission to use the photo below, with cross-sectioned spoke nipples. The spoke threads are the same length in all three examples, but the spoke nipples are of different lengths. A spoke can be threaded in only until the red line in the picture reaches the bottom of the threading in the spoke nipple. Beyond that limit, it will bind. The combination on the left risks breaking the spoke nipple just below the head, because the spoke does not extend up into the head of the nipple.

Only the short spoke nipple at the right is really suitable for the spokes shown. Reports of the demise of this Web site are greatly exaggerated! We at sheldonbrown. Harris Cyclery has closed, but we keep going.