Originally Posted by
FrankthePainter
Large arbor reels offer greater retrieval rate with less backing. For example, an Orvis BB III reel has a small arbor, but with 150 yards of backing wound on, the fly line revolves around an "arbor" that is roughly 1.65 inches. A Ross Evolution #2 has an arbor that is already 1.75 inches in diameter, and will give you roughly the same retrieval rate without all of the backing used on the Orvis BBS. That's good and bad, as the Evolution will not take much backing even if you want it. The real large arbor reels like Sage's 4500 series offer a spool with a large diameter in light weight sizes, and also enough spool width to allow: 1) more backing; 2) more fly line to fit at the larger diameter portion of the spool. Large arbor reels allow the drag to remain more constant as the line is taken off the spool, but only if the diameter of the remaining line doesn't change too much. Spool up the aforementioned Orvis BBS reel with 150 yards of backing, and begin pulling it back off. The drag will become increasingly stronger as the line diameter decreases. I have 3.5 inch large arbor reels that sucks line in like a vacuum cleaner, and that's something that you can measure quite simply yourself: pull a section of marked (small piece of masking tape will do) line off the spool, turn the handle one revolution, and measure the amount of line retrieved.
P.S. Tailingloop seems to have added the information I posted while I was posting. I don't want anyone to think I was trying to be redundant. ;)