Originally Posted by duker
Wow! Thanks for doing that Dan.
When the ice finally melts up there, I reckon we won't be hearing much Dan!
Seriously, that is great stuff Dan. I may try the common cents method since I have I bought an unmarked 11' blank that the seller claimed to be a 3/4 based on this method.
Anyway, I've done a little further research on AFTMA line designation and grain weights. This is a good chart:
AFTMA standard fly line weights
(grains per first 30 feet (9.1 m) of line)
Designation - Weight (grains) - Acceptable range (grains)
1wt 60 54-66
2wt 80 74-86
3wt 100 94-106
4wt 120 114-126
5wt 140 134-146
6wt 160 152-168
7wt 185 177-193
8wt 210 202-218
9wt 240 230-250
10wt 280 270-290
11wt 330 318-342
12wt 380 368-392
Rio give a full chart of every line on their website, which is really quite nice of them. It is really helpful when compared to the above to see where their lines fall. The Rio Grand line definitely falls into the line weight designation of one higher, but not exactly by a full line weight (using grains). For example, a Grand 5 WT line is 155 grains in the first 30', so it lands at the light side of a 6 WT line. This is true of all the lines within the Grand family.
The only S.A. line that I can find a chart for is the GPX, which works out because it is the cousin of the Grand - heavy, short, aggressive tapered head. A 5 WT GPX is 150 grains and rightly described as a half line heavy falling right in between a 5 and 6 WT.
Rio Gold on the other hand, is within range of the weight designation, but at the top end. A 5 WT Gold line is 146 grains, the maximum allowable for AFTMA standard. And it holds true for each weight in the Gold line.
So I don't that line manufacturers are sending out misinformation, particularly not Rio who has all the technical info on every line listed at their website. I think it get convoluted when Sage builds a taper with a Rio Gold or Grand line in mind, so they call it a 5 WT considering that it will cast optimally with a Rio Gold 5 WT line, which is a little heavier than the standard but withing the range. I think it's good that there are lines of varying grain weight, since there are more tapers to rods than we can imagine. If you use system Dan explained, determine the ERN of your rod, most likely it isn't going to fall squarely in the middle of on of the rod weight designations and you can pick the line weight (in grains) most closely suited i.e a heavy 5wt or light 7wt or what ever it is.
Plus, after all that, personal preference is still the factor that cannot be measured. But it's an important one.
I'm off to determine the ERN of my XP...