Talk:ISO 5775
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[edit] ERD really means Effective Rim Diameter
I have discovered an interesting point of confusion. "ERD" is used to mean two different things: European Rim Dimension, and Effective Rim Diameter. The latter is what it means most commonly in general use. The former is usually called "ISO," "European," or "ETRTO" size. This is an unfortunate confusion, because both of these are specified in mm, and usually they aren't any more than a few centimeters different. However, if you get them mixed up, you're going to have problems, as one refers to the tire bead size, and the other is most commonly associated with the spoke length. I think this article needs to mention this. What would be the best way to do this? AaronWL 23:25, 3 July 2006 (UTC)
Regarding the expansion of the ERD acronym, judging from the number of search hits, it looks like Effective Rim Diameter is the true expansion. And all of the bad hits are actually copies of the wikipedia page (*sob*). Trying to remember where I had got the wrong expansion from, I found this link in my bookmarks: One of the few rim manufacturers who actually give the ERD for their rims. At the top of that image is the bad expansion. I will replace it with Effective Rim Diameter.
Regarding the difference in measurements, again judging from a web search, the ERD appears to denote the rim diameter as used for spoke length calculation -- at the nipple seats, not the tire bead seat.
Opinions differ whether the ERD is measured at the nipple seat (eyelet surface, if the rim has eyelets) or the nipple head. Since the Effective Rim Diameter is by its name a property of the rim, I prefer the "nipple seat" definition. However, for some aerodynamic rims, the nipples must be mounted with the head pointing towards the hub, requiring the spokes to protude much further through the nipple seat. Conclusion: If given an ERD value, ask what it means exactly before using it.
--RainerBlome 14:25, 29 July 2006 (UTC)
- I'd favour the ERD section (added 7 Nov 2005 by RainerBlome) to be removed again. I wrote this originally as an article about the ISO 5775 standard, and ISO 5775 does not use the term ERD anywhere. This was not meant to be a generic article about all issues concerning rim and tire dimensions (but could be merged into such a broader article one day). The ISO 5775 standard is primarily concerned with the interface between rim and tire (and to some degree also with tire clearences). ISO 5775-2 does not talk in any way about rim dimensions related to spoke lengths. ISO 5775 does not mention that a rim might have spokes. Markus Kuhn 16:26, 29 July 2006 (UTC)
- I think ERD should be kept until a broader article is created, as its related; if removed, it should be moved to its own article or part of some other article. However, I'm almost positive that ERD relates to the tire bead, not the nipple seat, as mentioned. I beleive this partly because I've actually measured this distance on my rims, and partly because all rims that take a certain type of tire have the same ERD, yet do not have the same nipple seat diameter. AaronWL 10:21, 9 October 2006 (UTC)
