Hi everyone !
I am planning to build a new trial wheel with a mad4one 19” rim with big holes and an exceed hub but I can’t find the ERD of the rim on the website, do you know what is the ERD of this rim ?
I called Marco and he told me I can use 180 or 181mm for the spokes because, when the wheel is lanced with 4 crosses, the length does not vary much.
So if you know the ERD of the rim or the length I should use for an exceed hub I would be grateful !
Vival el Trial as a famous guy said once 
@MAD4ONE shall know.
I called Marco and he don’t know the ERD. Honestly I don’t even know how it is possible to produce a rim without knowing this but that’s another debate
I have built some unicycle wheels myself, and it is important to know a few things to calculate the spoke length you need. If you do it yourself by using 3d trigonometry you won’t have many problems as long as you know what spokes and nipples you are going to use and you can fit them in the rim and measure some sort of rim diameter suitable for spoking.
BUT most people use an online spoke calculator, where you put in a few measurements and the spoking pattern etc. as well as the “infamous” ERD value and out comes a number. Funny thing is different calculators give different results anyway.
If you search for how to measure ERD you might find some advice that gives you the distance which can be reasonably well defined from the spoke head “seating point” to the same point directly opposite, but this (although it is a VERY GOOD, well-defined measurement) is NOT the ERD - it is the NSD (nipple seat diameter). ERD actually depends on what spokes you are using and whether you are using washers under the nipples, so it is an impossible figure for a rim manufacturer to give (because they don’t know what spokes you are going to use).
Anyway, you probably want to know what length spokes you need (based on ERD etc.). But you also need to know if you want the spoke thread to go all the way to the end of the nipple when perfectly tightened or if you need to avoid protruding threads and have the average spoke a bit shorter. You also need to know the thread length (and if you are having spokes cut for a particular wheel because standard ones available are not quite right, you can usually specify the thread length - bit more thread might look ugly but allow proper tightening for all the spokes).
So, I guess what I am saying is that wheel-building is not trivial, may involve trial and error, and that ERD is a poor concept which is interpreted several ways, and which cannot reasonably be expected that the rim manufacturer would be able to quote a value, given that many different types of spoke nipples might be used.
And yes, 4 cross gives a bit of latitude - various lengths will probably work - it certainly doesn’t have to be accurate to less than plus/minus a millimeter!
Good luck with your wheel build!
With any rim, whether an ERD figure is provided by a manufacturer or not, I usually measure ERD myself and use that for calculating spoke length. Ideally ERD would be measured using whatever spoke nipples you’d want to use with your build, though if you don’t have them already lying around it’s not a big deal. You might only be a millimeter or two off if you’re using regular shaped spoke nipples.
Yes, I have used this technique in the past but I don’t have the rim with me right now and needed spokes length today because the bicycle shop where I buy the spokes closes for Christmas. I was too excited to build this wheel to wait for the re-opening of the shop.
Unfortunately he blocked his machine and wasn’t able to give me spokes so I will have to wait for the reopening anyway 
I’ll have my rim around Christmas so I’ll mesure the ERD myself on the rim.
Just need to be patient like every kid before Christmas 
I dont know how accurate it is, but in my notes I have 362mm. It may be good, it may not hahaha. Sorry I can’t help more than that!
I have to defend Marco here. He doesn’t manufacture the rim himself. When you buy rims in Asia, you usually don’t have any information about the ERD (European Rim Designation). But you can ask them. Often, the companies that supply the rims aren’t the manufacturers themselves, but rather distributors.
Yes, true but the ERD value is a very useful indication and on my opinion it should be mentioned on every rim
The ERD means Effective Rim Diameter, which is needed to build wheels. Distributors, resellers or even manufacturers should measure and share this info on product pages to make it easier for customers to buy their spokes. Without knowing the ERD, there is no way to know* which size spokes you need.
*You can only guess without the ERD, you can’t be sure of your measurement.
My professional wheel spoker doesn’t care about the ERD specifications. He measures them himself, because, as he says, these specifications are often inaccurate. He prefers to measure them himself.
For the 36“ Brauss CF rim, I remembered I measured it and informed Roger for his spoke calculator as my measurement was a litle bit different from Brauss information
This is the definition of ERD of a german wheel builder, it explains the different measurements:
ERD is the abbreviation for “Effective Rim Diameter”. The ERD or effective rim diameter is the diameter of the bicycle rim between two opposite spoke holes, i.e. the inner diameter of the rim plus twice the thickness of the rim base. You need the ERD or effective rim diameter to correctly calculate the right spoke length for wheel building.
Please note: Some rim manufacturers sometimes specify an ERD that is up to 4 mm larger, namely the diameter on which the spoke ends lie. At Kurbelix, we measure all rims in our range and uniformly specify the ERD rim inner diameter plus 2 x rim base thickness.
Translated with DeepL.com (free version)
From Youtube university:
plus 2x eyelets thickness?
You can work our the ERD of the rim by using our spoke calculator.
Spoke Calculator | Unicycle.com (UK)
The spoke length should be between 180 and 181, as this is what Marco says is what is used…. now change the ERD if you need to on the calculator until you get the spoke length right. That will give you the ERD of the rim.
I’m straying from the topic, but I saw in the unicycle.com spoke calculator that the dimensions of the QAXLE KH boundary and QU-AX disc hub flanges differed by 1 mm (57 mm for KH and 56 mm for QU-AX), whereas the non-disc versions have the same dimensions (57 mm diameter). I thought they were manufactured differently, but someone told me that they are the same product and that the only difference is the color. Does anyone have the answer? Thanks!
They are the same. I will check. It is possible we are using data we are given for this, not actually checking it ourselves as we normally do.
To add to the conversation/confusion regarding having to know what nipple type you are using, I bought some of these ERD sticks a while back so I would always have something set up for the particular nipple I was going to build a new wheel with before I ordered the spokes. As you can see from the picture, the different nipple types shown will have different amounts of spoke thread inside them and hence that will affect the spoke length you need. These are supplied with the nipple thread-locked on to set it at the “proper” length for thread engagement (as determined by a professional wheel builder).
As I recall these are ‘set’ to be 150mm (from memory), so you just put them in diametrically opposite holes, measure the distance between them and add on 300mm (assuming they are actually 150mm). The accounts for the nipple type and thread insertion. I have been using Sapim Double Square nipples for recent wheel builds and as you can see from the phtoto these have more thread engagement and hence required slightly longer spokes (nominally at least).