I wore a shoulder rack until approximately 2013. Please don't judge me. I started climbing in 1992. It's hard to change and evolve. But after 21-years of shoulder slinging, I finally switched and began to shoot from the hip...
Why would you subject yourself to a shoulder sling, you might be asking?
Easy, there are a number of advantages to racking on a shoulder sling.
Shoulder Sling Advantages
1) It's easy to shift a shoulder sling from one side of your body to the other when climbing off-widths or chimneys.
2) When you climb sport routes, nothing changes on your harness.
3) It's very easy to swap leads by handing the rack to your partner. Indeed, on some speedy ascents, we actually used to hold the sling out so the climber following the pitch would climb right up into the sling and then keep going...!
4) It's easy to see the gear that you have on your rack. Nothing is hidden on a gear loop at the back of your harness.
5) In steep snow, with a lot of clothing, it may be easier to find gear on a shoulder sling.
But there are also a lot of disadvantages.
Shoulder Sling Disadvantages
1) A large rack rubs your shoulder and neck raw. It can be very painful to carry doubles or triples.
2) On low angle terrain, the rack constantly gets in your way. It's hard to see your feet.
3) The edges of cams commonly get caught on edges while you're climbing, making it difficult to move efficiently.
4) Shoulder slings with fixed loops tend to change positions on your shoulder. Heavier gear constantly pulls the rack into inopportune positions.
5) If you fall and flip upside down, it's possible to lose the entire rack.
If you look at the advantages and disadvantages of a shoulder sling, it starts to feel like it's about even. There are five advantages and five disadvantages. But choosing whether to use a shoulder sling or to "shoot from the hip" isn't so much about the advantages and disadvantages of the shoulder sling, it's also about the advantages and disadvantages of racking on your harness.
Advantages of Racking on the Harness
1) Nothing is rubbing on your neck or shoulder.
2) You can see your feet. Additionally, there's nothing in front of you, so it's easier to see mid-level holds.
3) The edges of your cams are less likely to get caught.
4) Ice screw clippers work extremely well on a harness, but don't work at all on a shoulder rack.
5) Everything feels cleaner and more streamlined when it's on your harness.
6) Most climbers use this system. This makes it easier to work with lots of different partners while having similar systems.
Disadvantages to Racking on the Harness
1) Depending on the harness, gear may be hanging in awkward places. This is especially true with harnesses that have offset gear loops. It can be problematic when cams are hanging over the front of your thigh.
2) It's harder to swap gear between leads.
3) It can be hard to see which cam is which at your waist. I personally rack my cams with carabiners of corresponding color to easily find what I need on my gear loop.
4) There may not be enough space on the gear loops to accommodate all the gear required for a lead.
How you rack is ultimately a personal choice. But I do lean toward racking on the harness. The main reason for this is because I did rack on my shoulder for over twenty years. I didn't want to change. But when I finally committed to updating my system, I found it to be much more streamlined.
That said, I don't put everything on my harness. I still put some slings over my shoulder. So you could say that my technique is a bit of a hybrid...
If you're new to climbing, I would strongly suggest that you try both systems. There is value to being able to accommodate different systems for different kinds of climbing. But ultimately, you're going to lean toward one system that you use most of the time. These days, it's highly likely that you'll lean toward "shooting from the hip." However, if you decide that the shoulder sling is better, there's nothing wrong with that. How you climb is completely up to you...that's one of the cool things about this sport!
Jason D. Martin