Fly Reel designs have changed a lot in recent years. From the odd-but-now-classic Ari T. Hart to the space-age Lamson Vanquish to the neo-classics like the Hardy Lightweight. Everyone is trying to build a better mousetrap, so to speak. That's one of the reasons we work so hard to bring you great reviews like the 8-weight Challenge and 5-weight Reel Shootout.
One key design feature that a lot of questions have been asked about is spool width. In particular, one particular review claimed that they preferred wider spools. We're here to tell you that that is false, and we'll prove it with some basic geometry. Wider spools are significantly more prone to having fly line pile up and case a jam in your reel. That means you're going to be acting as a level wind, which is no fun, particularly if you've got a fish on. Here's why:
Wider spools are inherently shallower for a given amount of volume. Think about a long skinny rectangle vs a tall skinny rectangle. Because of that shallow depth, fewer turns of fly line will fit vertically on the reel. So, it only takes a little bit of line to hit the bar and cause a jam.
Narrow spools, on the other hand, are deeper. This means that you've got lots of room for that fly line to pile up before it becomes a problem. In fact, narrow spools are designed for fly lines to go up rather than out. To better demonstrate this, we're included the following animation of a reel's cross section: