The 5-weight may be the dominant size for much of the freshwater trout scene, but I've always had a real soft spot for a 4. I got my first 4-weight back when I was just a kid, maybe a year or so after I began fly fishing. There was something about that rod size that just connected with me and I've had one in my arsenal almost continuously ever since.
Many fly anglers might be inclined to pass up on a 4-weight, citing that it would be too similar to a 5-weight which most folks likely own at least one of. There's no doubt the 5 is awesomely versatile and shouldn't be ignored, but despite those two rod sizes being so close together, there is a noticeable difference between them. This difference in feel and power means the 4 can definitely offer some real value and enjoyment to those that target not just trout, but also species like panfish and bass, too.
Why is this? What applications can a 4-weight be used for? Is a 4 right for me?
Delicate Applications- A 5-weight is a great rod for trout because it can handle many streamers, general nymphing duties, and of course dries. However, when delicacy becomes more important, the 4-weight is the better pick. Not only will a 4-weight fly line cast with a little less authority and land slightly softer, but the rod itself will also do a great job at protecting lighter tippets. For even more delicacy and fun, choose a 4 with a moderate or moderate-fast action.
Still Fine for Bigger Stuff- There is a common misconception out there that you absolutely need a heavier rod for casting streamers. Don't get me wrong, this is true when dealing with larger patterns and added complications like sinking lines and a brisk wind. However, a 4- weight (especially with a faster action) makes a fine streamer rod for smaller patterns both weighted and unweighted. Locally here in Florida, I've used and still use a 4-weight all the time for largemouth and peacock bass when tossing clousers, buggers, general baitfish imitators, little poppers, and more. While a 4 has more delicacy than a 5, part of the reason I like this rod size so much is because it offers finesse while still having just enough power to not be super limited in its usage.
Makes Smaller Fish Fun- If you typically fish a 5-weight on bodies of water that contain mostly smaller fish, try dropping down to at least a 4. It's crazy how doing so can make the fight noticeably more enjoyable. The less-powerful, lighter-weight rod and thinner line all combines to make for a totally different feel that only amplifies the thrill of the fight. I've always enjoyed using lighter gear when practical and appropriate, and the 4-weight helps me get my light tackle fix.
What About Wind?- A 4-weight doesn't become useless when the wind starts blowing. I've fished them in brisk winds many, many times without issue. In fact, I have even fished a 1-weight in a fair breeze once and it did far better than I ever expected. The 4 has its limits just like every other fly rod out there, but those limits are not nearly as low as some may think.
What Species is a 4 Good For?- This rod size is excellent for several common freshwater fish. It not only makes an awesome lighter general-purpose trout rod, but it's also appropriate for applications like light-duty bass and carp fishing. Saltwater anglers could even find uses for a 4-weight on species like small bonefish and snook.
If you fish a lot and your finances allow, it's both fun and useful to expand your collection of rods to include additional line weights, even if they will be used for the same species. Doing this really allows you to maximize the experience and fine-tune your fishing to the conditions at hand. As you can see here, I'm a huge fan of the 4-weight and surprisingly even owned one long before ever getting my very first 5-weight. It has been an important line weight for me over the years and truly think it's one of the best and most useful that you can have. If it sounds like a 4 might be right for where and how you fish, I urge you to give one a try!