I'd just keep an eye on the exposed sections and see if it's getting beat up or wearing. If you pull your sled over a lot of big rocks or something I'd add all the runners you can. My one man only has two runners, every other sled I've had has at least 3, but it's been fine. I also hand drag, mostly got the runners because I pull across concrete from time to time. I can tell the runners are seeing a ton of wear compared to the rest of the sled.