Spoke Calculator

Pro Wheel Builder has made a reasonable effort to ensure the accuracy of data used in the component database. However due to the large amount of information contained within our data base as well as the rapid nature of manufacturer changes, inaccuracies are possible. Neither Pro Wheel Builder nor any of its employees makes any warranty of any kind for the information provided, express or implied, including but not limited to any warranties of merchantability or fitness for a particular purpose. Nor shall the distribution of this information constitute any warranty. It is your responsibility to confirm the length accuracy of your spoke order.

Step 1. Choose the Wheel or Tire Size - This is an optional input which will calculate the Rim Correction Factor used in the Sutherland's Handbook for Bicycle Mechanics spoke calculation system. It uses the Effective Rim Diameter value to determine the Rim Correction Factor. This is useful for updating a Sutherland's Manual with information about a new rim that may have been introduced after the current manual was printed.

Spoke Calculator

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Step 2. Enter the Effective Rim Diameter (ERD) - Also called Rim Spoke End Diameter, this is the diameter from one spoke end to the opposite spoke end in a fully tensioned wheel. The measurement is actually from the base of the screw driver slot of one nipple to the same location on another nipple directly across the diameter of the rim. It can be measured by using a commercial product, such as the Wheelsmith Rim Rods, or by measuring using the steps below. Please note: This is a very important measurement and lack of accuracy will greatly affect the final spoke length! Measure carefully, double checking each step to insure accurate results.

Step 3. Enter the Hub Flange Diameter - This is a measurement, in millimeters, between the center of one spoke hole to the center of another spoke hole on the opposite side of the same flange. Since it is difficult taking an accurate measurement from the center of a hole, it may be more accurate to measure from one edge of the hole to the same edge on the opposite hole. Use metric measuring calipers for the best results.

First, measure the over-locknut dimension (O.L.D.) of the hub, from the outside face of the left locknut to the outside face of the right locknut in millimeters.Next, working with one side of the hub first, then the other, measure from the face of the locknut to the center of the flange on the same side of the hub, then subtract that number from half the over-locknut dimension using the following formula:Left Center to Flange Dimension = (O.L.D. / 2) - Left Locknut to Left FlangeRight Center to Flange Dimension = (O.L.D. / 2) - Right Locknut to Right FlangeIf using off-center spoke hole style rims you must also do the following:

Step 5. Enter the Hub Spoke Hole Diameter - This is the diameter of the actual spoke holes in the flange. The default value of 2.5 mm works fine for most hubs. Hub spoke hole diameters range from 2.0 mm to 3.0 mm. Some higher quality hubs have smaller spoke holes so to achieve the ultimate in accuracy the default value can be changed.

Step 7. Choose the Number of Crosses - Choose the number of spoke crosses the wheel will have, i.e. 3 cross, 4 cross, etc. This is the number of times a spoke crosses another spoke during its travel from the hub to the rim. More crosses create a longer spoke, more tangent spoke, and more torsionally efficient wheel. Less crosses require a shorter spoke, but is less torsionally efficient. For this reason, most torsional wheels, like rear wheels and disk brake wheels, use 3 and 4 cross. Radial wheels (0 cross) should only be used in non-torsional applications, for example, non-disk brake front wheels

This is an easy to use and very accurate spoke length calculator. You can either enter your hub and rim measurements, or select from 1531 different models from the database. With 66749 calculations to date, you know you can trust its accuracy....

Before calculating the spoke length, make sure you have the correct ERD for your rim and the Flange Diameter and Flange Offset for the hub. It is vital these are measured very accurately, otherwise the spoke length will be incorrect.

As a precaution, when selecting a rim or hub from the drop-down menus, it's best to double-check the measurements with your items first. This isn't a warning to say the calculation will be incorrect, because it won't be. It's more to do with intolerance's between published and real-world measurements. This is mostly true (pardon the pun) for rims, as being out by 2mm or more can be the difference of having the right length spokes or not!

Getting ready to build a pair of mid-school wheels, and have noticed the complete lack of a decent spoke calculator for older hubs and rims. I know how to measure, but was wondering if anyone knew of a good online spoke calculator resource for the older stuff. All the online calculators I've found only touch upon the newer stuff, and being that I'll be building maybe three or four sets of mid-school wheels in the following months, it sure would be nice to find some sort of resource that does all the math...

Be aware that when determining spoke length from scratch, it can sometimes occur your results are less than desirable. This is typically from inaccurate data entered into the spoke calculators, not the spoke length formulas themselves. If this occurs, review your numbers and measurements.

It is important to use properly-sized spokes when building a wheel. Spokes that are too short can be identified by a lot of visible thread at the nipple. This is an indication of poor thread engagement, resulting in a weaker connection to the rim. 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.

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.

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. The common term for this is ERD, for Effective Rim Diameter, although a better term would be Effective Spoke End Diameter. 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.

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.

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. For front wheels with disc brakes, the wider side faces the rotor side. The purpose of rim offset is to help minimize the average tension difference between the right and left side spokes.

Using a caliper, measure the distance from one spoke hole to the opposite hole. We are trying to determine the distance from center to center, but it can be difficult to hold the caliper directly in the middle of the each hole when measuring. Try hooking one jaw on the inside edge of the hole and the second jaw aligned to the outside edge of the hole.

The next measurement needed is the distance from each hub flange to the middle of the hub. This is known as flange-to-hub center. This dimension accounts for varying flange widths as the spoke travels inward to reach the rim.

Many online calculators also have a field for spoke hole size. The default size is usually 2.5 mm diameter. Measure it to be safe, but even if your hub varies slightly, it will not make a significant difference in spoke length.

Spoke length is also influenced by the spoke pattern as they radiate away from the hub. The shortest spoke possible would go from the hub straight up to the rim, for a radial (or zero cross) lacing pattern.

Now consider hubs with one flange more inset than the other. For example: on a rear wheel, the drive side flange is pushed inward to make room for the sprockets. Accordingly, the distance from the right flange to the rim is shorter than from the left flange to the rim. When the flange-to-center measurements begin to differ between the left and right sides, we often get the option of differential spoke selections, meaning that different length spokes should ideally be used on left and right sides.

Generally, there is a one-to-two millimeter range of acceptable spoke length for a wheel. If you want to build with non-differential spoke selections, and the two spoke lengths are only one millimeter different, select the longer length for both sides, and the wheel will typically be fine. If the two sides are different by two millimeters, you can use the average of the two. However, when you get to a difference of three or more millimeters, it is best to build with two different sizes. e24fc04721