If I take a spinning rod rated at 10-17 pound line test, and run 15# line from the reel through the guides and tie it off, hold the rod butt 90 degrees to the tip that's pointing toward the tie off and start backing up, shouldn't the line break before the rod? I'm trying to figure out what the 10-17 pound line rating of a rod really means. Thanks.

I think you'll be lucky if you can get around 8 lbs of drag off a bass reel. My Quantum Cabo PT 31 just barely exceeds it. So you'll have to tie the line off to the rod to test your blank. I think if you tie off a full 2 liter bottle to your rod hold it parrallel to the floor and try to pick it up, you'll find out all you need to know without damaging something. Just barely got a 5 lb sack of flour off the ground with me heaviest musky rod.

It depends. Some blank manufacturers specify that with a dead load on the tip of the rod at 90 degrees(angle between the butt and the tip) with a line at the maximum line rating of the rod the line should break before the rod does. But as you decrease this angle or raise the tip higher you are transferring more of the load toward the tip and weaker portion of the rod and therefore the rod may break before the line does. But other manufacturers do not specify what they mean by the line rating.
There is also the variation in lines. There are some lines that may be rated as much as 50% low so that fishermen will think that they are really strong lines.
And there is of course the loss in line strength with the knot you use.
But after having said all of that, I think that the answer to your question should most often be yes.

15 pound test is line which breaks at more than 15 pounds. A line that has a breaking strength on a steady pull of over 100 pounds can correctly be classified as 15 pound test. That's a somewhat exagerated example, but 15 pound test lines all have a breaking strength of considerably more than 15 pounds.

With that said, yes the line should break first, but with any subjective rating it may or may not. And as Emory pointed out, how you use the rod will determine what type load it can take before breaking.

In many cases, the recommended line rating is just a suggestion based on what the designer expects most people will be using on said blank or rod.

.............

yep,
I have seen more than a few rods rated at 20lbs break with the user threading 15lb or less line thru it. Mostly though to user error
on the fishermans part.

Raymond Adams
Eventually, all things merge, and a river runs through it..

Never thought about it. I just built a rainforest RT 6320. I think its 20#'s, and 63 inches long. I got a Cabo pt on it, ran the drag all the way down till it was hand tight, (tight now, no more clicks.) and picked up a 10 pound weight. Oh, 20# braid line. The rod made all sorts of crunchy noises as the wraps stretched, or the epoxy microcracked, or something. Got the weight off the ground, for a second, then the drag let it back down. I thought that rod would pick up 10 pounds no problem. Oh yeah, I did it cause I read your post, not some coincidence or some such. I think the rod would break, but there was enough strain I got kinda scared. I got another blank, exact same. I don't know, though.... Levi

Levi,
Try tying that braid to a beam or something and see just how much weight it will hold.
I'm sure you will be very suprised!

Raymond Adams
Eventually, all things merge, and a river runs through it..

The idea of testing the strength of the rod blank with a DEAD WEIGHT that equals the UPPER END of the rod blank's LINE RATING is anathema, and is definitely inviting the rod blank to fail.

I would never expect a rod blank to endure more than 50% of its upper line rating in a dead weight load, at a 90 degree angle, and certainly not at more than a 120 degree arc. This comment is entirely SPECULATIVE on my part. I have never tested, under controlled conditions, a rod blank this way, with that much drag (more like 1/3). I'm afraid the test may be successful and prove that the rod blank WILL indeed fail at anything above 50% of its top-end line rating. I can't afford to be popping rod blanks just to satisfy my curiosity or penchant for scientific experiments.

IMO, the big picture is that the REEL DRAG should be set to low enough to SLIP, LONG BEFORE a halt or chatter in the drag washers can cause a high enough PULSE stress to build up and OVERLOAD the rod blank. This of course is much more of an issue when using SUPER-BRAID lines, which have NO STRETCH, than for nylon monofilament, which has well over 5% stretch.

IMO, -Cliff Hall+++ Merry Christmas

Cliff,
I think that Tim's question was more directed at what does the line rating on a blank mean.
I did some distructive testing on some blem blanks, I had a lot of them, a year of so ago as a result of a discussion that Tom and I were having about where rods break and why. It turns out that with a dead load at 90 degrees blanks will take several times the load that they will take at a higher angle like 120 degrees and at a very high angle approaching 180 degrees they will break at a very small fraction of their max. line rating. Another interesting piece of this was I could make blanks break anywhere along the blank that I wanted it to break by varying this angle.

Emory,
That makes sense.