The most important step when building a bicycle wheel is determining the correct spoke length to use.
Whether you’re a professional bike mechanic or just an adventurous tinkerer looking to build your own bike wheels, finding out how to measure a hub and rim, and learning to calculate spoke length is crucial to building a wheel that is strong and reliable.
If you get this part right, the rest of a wheel build is easy. Get it wrong, and all you’ll have is a real mess!
At the first bike shop I worked in, we used the Wheelsmith spoke calculator. The kit consisted of a ruler, a pair of rods, and a pre-programed scientific calculator for measuring the parts and running the calculations. The complete package was expensive, costing $300-$400, and was not exactly intuitive to use, but it was a necessity at the time, and was able to get the job done well until the day the program on the calculator got corrupted or erased somehow and nobody seemed to know how to fix it! Fortunately we are living in the computer age now and free spoke calculators are plentiful.
Over the years I have had experience with a good number of different spoke length calculators, and have found most to give good results. This makes it hard to name just one as being the best for everyone.
A calculation is only as good as the data used to calculate it, so do your homework and remember to measure twice. Once you have found some success with one spoke calculator, spend some time with it, get to know your tool and continue paying attention to any variances and adapt your approach accordingly. As with any skill, experience counts big time when it comes to wheel building, and it pays to be consistent in your method.
These spoke calculators listed below are the best ones that I use or have used in the past to build great wheels, none of them will lead you astray, so choose the one you feel most comfortable with and then get to know it. Also, If you’re ever unsure, you can use more than one of these to check against each other for peace of mind.
1) United Bicycle Institute Spoke Calculator
The online spoke calculator provided by the United Bicycle Institute in Oregon has been my personal favourite spoke calculator for at least five years now. It was the first online spoke calculator I tried, choosing to have faith that an institute renowned for teaching and training people to become bike technicians wouldn’t host a spoke calculator that sucked! As it turned out, The first wheel I measured spokes for using this calculator turned out wonderful so I kept coming back to it for all subsequent wheel builds. The interface is beautifully clean and simple and the results it spits out have never let me down.
Pros: A simple and accurate spoke calculator from a trusted source with an interface that is easy to use and understand.
Cons: The available fields only allow for calculating one side of one wheel at a time. No database of pre-measured hubs and rims, (I prefer not to use other peoples measurements to determine correct spoke length, but there may be cases where you need to order spokes when you don’t have the physical rim or hub on hand.)
2) DT Swiss DTool Spokes Calculator 2.0
The DT Swiss online spoke calculator is very popular with wheel builders, and I don’t have a hard time seeing why. If you’re using it for the first time, you can trust that it is of the same level of precision that the Swiss spoke, hub and rim maker has long been known for. It can be accessed for free with or without signing in, but if you build a lot of wheels and use this calculator often then I highly suggest taking the short time to register and sign in for some added features. The site allows you to enter all the data for a complete wheel set before calculating, and if you are a registered user you can save your measurements for future quick reference, and can email or print the results. The main advantage of this spoke calculator comes if you are building a wheel using DT Swiss’s excellent components. It has pre-measured data for all DT hubs and rims, as well as spokes and nipples. It even gives an estimated weight for the final build!
Pros: Ability to measure both front and rear wheels on the same page and print the results. Registered users benefit from having a saved database of their own wheels on hand for future reference. This spoke calculator makes the most sense if you are building up a DT Swiss hub or rim and using their spokes already.
Cons: Interface is a little clunky, and not the most intuitive, which may make it a little tougher for the first time wheel builder to get a feel for.
3) SpoCalc.xls by Damon Rinard
This spoke calculator by Damon Rinard differs from the other two spoke calculators mentioned previously in this post. It is written using Microsoft Excel 5.0, and is freely downloadable. The user only needs a program compatible with Excel spreadsheets, such as Microsoft Excel, Open Office or Libre Office. Spocalc includes a large database of hubs and rims that can be adjusted and added to by the user. The beauty of the spocalc program is it makes a great offline alternative if you ever find yourself, (gasp!) disconnected from the online world of the internet. It is by no means the most user friendly spoke calculator I’m going to suggest, but works great and many professionals will swear by it. There is also a version named SpocalcExpress that does away with the database leaving you with just a simple set of fields to generate spoke length one side at a time.
Pros: A great functioning calculator that lives on your hard drive. Spocalc has a pretty good sized database of hubs and rims that you can change or add to yourself.
Cons: Well, it’s an Excel program so it has that spreadsheet style that just kinda turns you off! The database, while potentially useful hasn’t seen an update in quite some time as far as I can tell.
If you are interested in using an online spoke calculator based on the spocalc.xls program and database, there is one at this link: http://leonard.io/edd/
4) Wheeler App for Android
The world of technology is moving at a quick pace. What does this mean for bike mechanics? It means that if you have a smartphone you’re actually carrying a spoke calculator right in your pocket! Yes, there’s an app for that. I have and android phone and there are several apps for measuring spoke length available in the Google Play store. I’ve started using one that has been working really good, and happens to be free. Wheeler is a perfectly basic spoke calculator app that has data fields allowing you to calculate both sides of the wheel at once, and also has the feature to save a wheel after you’ve measured it for future reference. With the Wheeler app you can have the spokes measured for a wheel and saved to your phone before you even get to the computer to open a web browser. Awesome!
Pros: A fast, accurate, simple and lightweight spoke calculator app for your android phone. What more can I say? The ability to save the wheel afterwords is a great feature.
Cons: As of writing this article, (October 2013) there is just one caveat I have with the app. One of the fields reads: “Center to flange distance.” You would be forgiven for assuming that meant exactly what it does on every other spoke calculator, the distance from the center of the hub to the center of the flange. However, if you enter that measurement into this tool you get some pretty funky spoke lengths. What this field actually requires you to input in order to make an accurate calculation is the distance from the outer locknut to the center of the flange. The app already requires you to enter the OLD (Over Locknut Distance) and uses that alongside the distance from the locknut to flange to then calculate the center to flange measurement. Yeah, the wording is wrong and will create errors if the user is not aware. On the plus side, once you see how it works it does make measuring up the hub one step quicker. I contacted the web developer to point out this one problem with the app and he returned my email a day later to say that I had a good point and he will correct it ASAP. The version I’m using to write this post was uploaded on September 27, 2013 so hopefully by the time you read this article, the correction has been made and the app is perfectly user friendly.
I haven’t tried any spoke calculators on the iPhone, but this app seems like it is just the thing: Spoke Length Calculator – Apple iTunes Store
5) Nature’s Calculator – The Human Mind
Does the equation and diagram above mean anything to you? Don’t feel embarrassed if they don’t. I’ll bet that most of even the best bike mechanics are left singing Jimmy Buffet songs to themselves in their heads at the mere sight of them. Math never was my strongest avenue of expression in this world so I probably won’t stress to long over equations like this. I know that there are some smart people out there that we’re lucky to have around. It’s people that speak the language of these diagrams above that make all these fantastic toys we play with possible. Every fill-in-the-blanks spoke calculator I’ve shown you is based on the application of these concepts, so it might be respectful to look at them for just a little while and contemplate the effort put in by gifted people, (the smart mathematicians who figure out these equations, and the clever computer programmers who wrap them up in the software code,) so that us more mechanically inclined individuals can feel like we are actually good at something too.
If your brain is capable of handling it, some more details regarding the math involved in determining the spoke length of a wheel can be found here.
Need some helping getting started building your first wheel. Here is a good place to start: http://sheldonbrown.com/wheelbuild.html