ERD measurements gone haywire
I followed the instructions on http://www.wheelpro.co.uk/spokecalc/
and put a piece of tape at 200mm on two spokes so that makes 400mm. Then I measured the distance between the two pieces of tape which was 108mm. So, that makes 508mm. I measured the spokes on my broken wheel and it looked like 265mm. However, it's a single wall 26 inch rim so I figured maybe the ERD may be similar to other cheap rims. So I looked up the Alex X-202 rim and the ERD is 547mm. So, I entered that in the calculator and it gave me 263mm for spoke length. The spoke I measured may be 263mm depending on how I measure it. Like if I start measuring from the middle of the rounded end.
Then I looked at my 700c WTB Freedom Ryder 23 rim and I know it's 597mm. I can't even remember how I calculated that in the past. Anyway, I used the same method with the two spokes on the Ryder 23 rim and it was 260mm. So, I decided to add 37mm to 508mm and it gives me 245mm. OK, I don't know if there's really a difference of 2mm with the rim I wanted to buy but would that be a problem?
How/why is the two spoke method not giving me the real ERD?
EDIT: I might choose the Alex DM24 because it has an internal width of 24mm which I think I'd need for 1.95' tires.
Last edited by hybridbkrdr; 08-19-11 at 08:09 PM.