1 year ago

How to measure ERD (Effective Rim Diameter) of a rim that is on a wheel that is finished.

- Contents -
00:00 What is ERD (Effective Rim Diameter)?
01:05 Why is it important to measure ERD?
02:14 Why measure a rim in a built wheel?
03:38 Tools that are needed
05:20 Measuring distance from rim's outer side, to nipple's top
07:57 Measuring rim's outer circumference
09:49 Calculating ERD from our measurements
10:46 Conclusion

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The calculation (formulas):

π ("Pi") = 3.14
Circumference = 2 ⋅ Radius ⋅ π
Diameter = 2 ⋅ Radius
Circumference = Diameter ⋅ π
Diameter = Circumference / π

That's how we calculate the outer diameter from the measured circumference.

Then, to get the ERD, we need to:
- Measure the distance from the outer rim's edge to the spot where the nipple is seated.
(This is noted as X1 for ERD1 and X2 for ERD2 in the video's example graph)
- Substract the double of that from the outer Diameter (because we have that "extra" on both ends of the rim).

So:
ERD = Diameter - (2 ⋅ X)
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- Useful links -
If you have any questions, please use the BikeGremlin forum (I try to respond to every comment, but YouTube sucks at notifications, especially when it comes to any follow-up questions):
https://www.bikegremlin.net/

Effective Rim Diameter (ERD) explained, and how to measure it (article):
https://bike.bikegremlin.com/9266/effective-rim-diameter/

Video about measuring and making spoke length calculations:
https://www.youtube.com/watch?v=i5ywzfr_dCg

Bicycle tyre sizing standards explained:
https://bike.bikegremlin.com/285/bicycle-tyre-dimensions/

Accurate vs Precise:
https://bike.bikegremlin.com/8374/accurate-vs-precise/

Datasheet with ERD-s for the rims I've (measured and) written down on BikeGremlin website:
https://bike.bikegremlin.com/9503/erd-data/

List of all the BikeGremlin videos, sorted by categories:
https://www.bikegremlin.com/youtube/

Camera: Mika Häkkinen

id: 1039

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