A critical part of getting a wheel build right, is using spokes of the right length.
Get the spoke length wrong, and you run into some problems.
- Too short, and assembling the wheels becomes tricky. You also risk the nipple head snapping off, as it may have enough internal support.
- Use spokes which are too long, and you risk not being able to tension the spokes sufficiently, and the extra spoke extending through the top of the nipple may puncture your tube.
What length spokes do you need?
This is something you need to figure out.
You need the hub dimensions, and the effective rim diameter (the diameter of the circle of the top of the spokes, inside the rim.) This is also known as the ERD.
Once you have accurate measurements of the above, simply enter the dimensions into an online spoke length calculator, such as one of the ones below:
Once you have the required lengths, you simply need to get them.
Simple right? Not really.
Hub dimensions
Most hub manufacturers publish their hub dimensions fairly reliably – as a rule of thumb, you can use these measurements. Here is Hope’s hub dimension chart.
Rim dimensions
Actually measuring the effective rim diameter is crucial, as many brands list this measurement EXCLUDING the nipple head height. For standard nipples you add 2mm per nipple, for internal nipples you may add 6-10mm and for DSN or squorx nipples, you may add 4mm… confused yet?
To get this right every time, measure manually. Here’s how to do it.
- Find 2 brand new spokes, longer than 300mm, and cut off the heads, leaving exactly 300mm of length, with the thread on one end. These are called rim rods.
- Take the nipples you’re planning on using for the build, and screw them onto the rim rods, with the end of the spoke flush with the top of the nipple, and superglue them in place.
- Insert each rim rod through opposite spoke holes in the rim you’re using for the build, so that they overlap in the center, and measure that overlap, and subtract from the total length:
2x 300mm rim rods, which overlap by 12mm, leaves an effective rim diameter (ERD) of 588mm. - This method works perfectly every time.
Still unclear? Get in touch and I’ll explain it again 🙂
2 Responses
You mentioned to thread the spoke flush to the top of the nipple while Park Tool says that a perfect build will have the spoke threaded flush to the bottom of the slot (where the hole on the nipple head begins/ends at the bottom of the rectangular slot). Is this the 2mm you’re talking about for a regular 12mm nipple? Why include the full nipple head height (flush to the top of the flared top end) rather than at the flush of where the threads end at the start of the rectangular slot area?
Ultimately, personal preference. If the spokes end anywhere between the bottom of the slot and top of the nipple it’s perfect. Bear in mind that most spokes are available only in 2mm increments, so having 1mm variance here and there is fine.