FLO Cycling – Effective Rim Diameter and Spoke Length

When building a cycling wheel, the Effective Rim Diameter (ERD) is an important measurement used to calculate the correct spoke lengths.  A lot of rim manufacturers will list the ERD of their rims (we do too), but it is very important to know that the ERD we list, can be different from the ERD you will calculate for your specific wheel build.  The short answer is because you may be using different nipples and components for your build then we use with our wheel builds.  Below is information on how to properly calculate ERD, and ERD values for our FLO Rims.

What is Effective Rim Diameter?
At FLO we use the technique defined on Sheldon Brown’s website to measure ERD.  That technique is defined as follows:

Effective Rim Diameter (ERD) is the diameter on which you want the ends of the spokes to lie. Most people prefer it near the end of the spoke nipple.

The corresponding equation and a representative figure for that definition are as follows:

ERD = A + 2B 

If you want to measure your own rim (recommended, just to be sure), then follow these instructions:

  • Insert two old spokes into holes exactly opposite each other on the rim. Count holes to be sure.
  • Screw some nipples onto the spokes.
  • Pull them tight and measure dimension A in the figure (the diameter to the edge of the nipples, where the spokes disappear into them). Do this at several spots around the rim and average the measurements.
  • Measure the length of a nipple (dimension B in the figure) and add it twice (once for each nipple). The result is Effective Rim Diameter (ERD). Thus,
  • ERD = A + 2B.

As you can see from the figure, if you use different nipples then we use at FLO, your ERD value could be different.  As a result, we recommend that you always measure your own ERD value before building your wheels.  For more specific information on how to properly complete the measurements above, we suggest you thoroughly read through Sheldon Brown’s website, or take your wheels to an experienced wheel builder.  

FLO ERD Values
Assuming you’ve read the information above, it is safe to say that you already know the values I am listing below are subject to change for your specific build.  That said here are the ERD values for FLO rims, and the components we use to calculate these values.  

FLO 45 Carbon Clincher: 548.4mm
FLO 60 Carbon Clincher: 513.9mm
FLO 90 Carbon Clincher: 452.3mm
FLO 30 Aluminum Clincher: 577.5mm

Spokes: Sapim 12mm Hexagonal Brass

Note: We build all FLO wheels with nipple washers and recommend you do the same.  We use Sapim HM Washers.

I hope this article has been helpful.  If you have any questions or comments.  Please feel free to leave them below.

Take care,


Join the Conversation


  1. Just a couple questions. I've had some fun building my own wheels, and am always interested in learning more. I'm obviously no pro, and don't expect my results to equal an experienced wheel builder, but am hoping you guys can share a bit of your wisdom.

    First: are spoke nipple washers needed for every spoke? I'm wondering mostly on a back wheel, where tension would be much higher on the drive side than the non-drive side(assuming the same lacing pattern on both sides). On a front wheel the tension would be equal on both sides, so I'm assuming washers for every spoke or none in that situation.

    Second: spoke washers regardless of rim material? I'll take you at your word since you said you use them on all your wheel builds, which would include the Flo 30, FLO 45, and the carbon fairing aero wheels. I've not used them on the three sets of wheels I've built, which were all alloy rims. But like I said, I'm an amateur with the Jobst Brandt book and a couple Bill Mould videos. I'm wondering if I'm just doing it wrong (always a possibility), or if there are some considerations that the pros take into account when deciding to use washers.

    Thanks for letting me pick your brains! Really enjoyed riding your wheels when I was competing in triathlons and aquabike races, and also enjoyed hearing y'all on the TrainerRoad podcasts.


  2. Ben,

    Thanks for writing and for the kind words. We are happy to hear that you enjoyed the TR podcast. It was really fun doing it. Also happy to hear that you are loving your FLO wheels.

    If you are going to use nipple washers, which I highly recommend because they help to distribute the load, then I would use them on all spokes.

    You don't have to use washers, but we just like to use them for the above reasons and hence recommend our customers do as well.

    I hope that makes sense,


  3. I bought two rims (the 60s) from you guys, and realize now I may have bitten off more than I chew myself. Since I have never built a wheel before. Can you guys give a recommendation on a front hub? I would like either the same hub on the standard build or something that uses the same size packaged bearings to make my life simpler.

  4. Arthur,

    Thanks for writing. I apologize, but I'm not sure I understand your question. Are you asking if I can recommend a front hub that uses the same bearings as our front FLO hub?

    With respect to building the wheel, I'd highly recommend reaching out to http://www.wheelbuilder.com/ or https://www.prowheelbuilder.com/ for advice. Both of these builders are experts and can help you select the right components for your build.


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