Dear Wheelbuilder,

Take a few minutes to read through this page and see how easy it is to work out spoke lengths for any hub or rim.

Hubs and Rims navigation buttons

The entries in the rims table are no doubt obsolete and the hubs are limitted to Hope Technology (because Hope use this calculator on their site and don't want other hub brands showing). This means your particular components are unlikely to be listed however it's easy to measure your components which means you can work out spoke lengths for any hub or rim - past, present and future! So do the same as I do, measure and calculate.

Entering the wheel geometry

Measuring hubs and rims is described later in this guide.

Enter your wheel geometry and click the calculate button.

If you calculate a spoke table then subsequently edit the dimensions remember to re calculate. If a spoke table is in view and you edit the dimensions then the Calculate button will change to indicate that the spoke lengths do not relate to the displayed components.

Wheel type

The radio buttons adjacent to the component descriptions indicate the type of wheel. The selection is used to determine the spoke table headings and which colours to use for the spoke lengths, for example if you alter the type from normal to disc then radial spokes for the disc side are shown in red. If you select a hub from the tables the appropriate values will be set, if you manually enter your values you need to select the wheel type yourself.

The spoke length tables

Use the calculate button to produce the spoke tables. You will notice that four colours are used. The specific colour is based on the number of holes, cross pattern, front or rear, and whether it's a disc brake hub:

White :	Preferred lacing patterns for the given drilling and cross pattern.
Blue :	Will work, but generally not preferred.
Red :	Not recommended. These lacing patterns should not be used. The reason is to avoid overlapping the spoke heads on the hub flange as the spokes become more tangential. The drive side and disc brake side of the hub should never be built radial because you need a cross pattern to transmit the drive and brake torque.
Grey :	Where radial is allowed the hub manufacturer always has the final say. Some manufacturers do not allow radial spoking because it can severely damage the hub.

Measuring hubs

Don't trust measurements you found on the Net or anywhere else, always measure yourself - both hubs and rims.

The key dimensions on the hub are shown below. The purple line is the centreline between the hub locknuts. Dimensions A and B are measured to the centre of the holes, dimensions C and D are measured to the inside face of the flange.

To measure C and D

Measure x and y shown in the photograph below , then:

C = Z - x
D = Z - y

Where Z = half width over locknuts.

To double check your calculations, C+D should equal the distance between the flanges which can be directly measured with a rule.

To measure x and y

See the photograph on the right. Take a block of wood and drill a hole in it to allow the hub to stand upright on its locknut face. Use a piece of card to mark where the inside face of the flange is then measure the distance on the card with a rule.

Always record your data, take a print of this hub sheet which is taken from my wheel building book.

Measuring rims

This is the Effective Rim Diameter (ERD) and you need to measure it yourself. It does not refer to rim sizing terms such as 559 etrto, 700C, 26" etc. Some rim manufacturers will quote the ERD in their rim specifications but you must measure it yourself because it is the most critical dimension in the spoke length calculation and the calculator assumes you use the following method for taking the measurement.

To measure it you need two old (straight) spokes cut down to 200mm (cut off the elbow side). Glue on a nipple so that the top of the spoke is flush with the bottom of the slot in the nipple.

Place in opposite holes in the rim and hold taut (do not apply so much force that the rim deflects). Measure between the ends and add 400mm. Average several diameters.

After measuring a few different rims you will realise that most rims are similar which again makes spoke selection easy. Even with a rim you've never seen before the chances are it's similar to one you've built previously.

By doing some analysis with the spoke calculator you will see that rim diameter has the greatest influence on spoke length (for a given hub), so measure it carefully.

Non standard components

18 holes

Putting in a range of rim drillings will miss out the 18 hole option to avoid cluttering the table with unnecessary information. If you want to calculate the 18 hole variant just start the range with 18.

44 holes

44 hole hubs and rims are non standard and are omitted in the spoke tables. If you need to calculate a 44 hole wheel then make sure the holes drilling range starts with 44.

Offset rims

The spoke holes in some rims are drilled off centre, some examples are the Bontrager ASYM rims. Offset rims are very rare and the majority of rims have an offset of zero. The offset rim manufacturer will advise the offset and it is typically about 2mm.

The accuracy of the spoke lengths

The spoke lengths from the formula (and this application) will be accurate provided you have measured your components carefully. In the first instance go with the calculated figures. If you cannot get those spokes (some stores only stock even sizes) then try 1mm less. Remember the calculation rounds the sizes to the required decimal places so it may be worthwhile calculating to 1 decimal place to gain more accuracy and so make a better judgement. 2 decimal places are provided for wheelbuilders doing analysis on how dimensional changes effect spoke length.

Spokes from all manufacturers should be the same. Use the calculated spoke lengths and build the wheel. Then examine the accuracy of the spoke lengths and if you find them to be slightly out for the brand of spokes used then compensate for this next time you use the calculator.

Roger Musson