How to calculate the length of the spokes for your bike?

spokes for your bike

How to calculate the length of the spokes for your bike?

Although you can indeed buy a wheel already assembled in almost any bicycle store and perhaps at a more accessible price, there are cases in which it is more convenient to build a wheel. If you are looking for a specific combination of rim and hub that is difficult or impossible to find in the market (e.g., you want internal changes on your bike). If you want to master the art of aligning a damaged wheel, starting from scratch is the best way.

Steps to calculate the length of the spokes for your bike

The spokes or spokes, as they are known in some countries, in addition to joining the hub with the rim, contribute to the resistance of the wheel. We can find them in various materials ranging from chrome steel, stainless steel, titanium to carbon fiber. Regardless of their material, it is important to calculate the length you need before buying them, either to assemble a wheel or to replace one that has been damaged.

A beam that is too short will not have enough chord on the nipple to tighten it and therefore represents a weak point.

A beam that is too long will cause the beam to protrude from the nipple and increase the chance of getting a puncture.

The easiest way to calculate the measure we need is to use an online calculator like the one from the United Bicycle Institute. This calculator seems quite practical and simple to use, so we will use it as an example in this post. Keep reading: Good mountain bikes under 500.

The first step is to select a hub and a rim from which you will obtain the necessary data to calculate the length of the spokes you need. We will not go into detail on the issue of hubs and rings. We will only comment that your choice should be based on the application and performance you are looking for.

This measurement can be defined as the distance between two opposing and tensioned nipples. In certain cases, this measurement can be found marked on the ring itself. If not, you can research it on the internet or measure it directly (recommended).

ERD (unassembled rim)

Measure the outside diameter of the ring. This measurement is taken from flank to flank of the rim. The hoop will not necessarily be a perfect circle, so I suggest that you take measurements at different points and take an average.

Place a nipple in one of the hoop holes and measure from the flank of the hoop to the base of the nipple groove and multiply by two.

Finally, subtract this distance (obtained in step 2) from the average outside diameter that you obtained (in step 1), and voila. You will have calculated the ERD.

Calculation of the effective diameter of the ring

There are other methods to obtain this measurement, but in particular, this is the one that seems the simplest to me.

Hub Flange Diameter

Technically this measurement is the diameter of the circle formed by the holes in the flank of the hub. One way to obtain this measurement is with a vernier, also known as a vernier, but how do I know that not all of us have one of these? We will use a sheet of paper.

Take your sheet of paper and cut out a crescent shape to allow room for the hub axle.

Then mark the position of two opposing holes with a pencil.

Finally, take a common and current ruler and measure the distance between both marks.

Hub flank diameter

This distance is the distance from the center of the hub to the center of the left or right flank.

In the particular case of the front wheels (without a disc brake), the calculation is simple since the rim is centered right in the center of the hub. In other words, the measurement from the center to any of the flanks is the same.

In the case of the rear wheel or front wheel with a disc brake, it is necessary to take into account the space that the pinions, the disc, or both will occupy, as the case may be.

For practical purposes, we are going to see how to obtain these measurements in the case of a rear wheel.

Obtain the overall length of the hub by measuring from the face of the left locknut to the face of the right locknut.

Divide the measurement obtained in the previous step by two to obtain the center of the club.

To obtain the length from the center of the hub to the center of the left flank, subtract the length measured from the outer face of the left locknut to the center of the flank of the same side from a distance obtained in step 2.

To calculate the distance from the center of the hub to the center of the right flank, repeat now it is necessary to subtract the distance from the right locknut to the center of the right flank.

Note:  In this case, you will have to perform the ray length calculation twice (L / 2 – i for the left side and L / 2 – d for the right side).

Hub Spoke Hole Diameter

The vast majority of clubs have holes that vary between 2mm to 3mm, so you can use 2.5mm as a standard measurement. Some higher-end hubs have smaller holes, so you can enter a lower value if required.

Number of Spokes in the Wheel

This number refers to the total number of spokes the wheel will have. Both hub and rim must have the same number of holes.

Cross Pattern

This pattern is defined by the number of times a ray crosses other rays on the same flank, from the hub to the rim. The less you cross, the length of the beam will be shorter and, therefore, a little lighter. On the other hand, the more you cross, the beam is longer. Also, having an angle tangent to the circumference of the wheel has more resistance to torsion. For the latter, the rear wheel must always have a tangential pattern. The front end can use a radial pattern as long as the disc brake is not used.

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