We are all familiar with the classic outside-inside-outside line for cornering, as it usually optimizes speed and distance for the quickest time through a single corner. But even that is open to debate if you consider an extreme example: Say you and your buddy are lined up on your minibikes at one end of a long, wide parking lot. At the far end is a single cone: what is the quickest way to get to the other end of the parking lot, around the cone, and back? The classic line dictates that you go to the very edge of the parking lot, arc wide around the cone and back to the other side, but that adds a lot of distance - most of it unnecessarily. Meanwhile, your buddy rides straight down the middle of the lot, brakes hard and pivots around the cone, riding straight back to the start in much less time.
The lesson here is that it's not always imperative to use the whole track on corner entry or exit, especially on a wide track or if you are on a bike that is not particularly powerful. Throw in bumps, camber changes, and corners immediately before or after that affect entry or exit speed and position on the track, and the quickest line can stray wildly from that classic arc. It's not overly difficult to work backwards mathematically from a corner apex to find the best line for a single corner based on a handful of assumptions; in fact, there are software packages that will determine the optimum line for an entire track, given enough detail. But even the most elaborate software can't know that its calculated fast line for a given corner is full of bumps, or leaves the door wide open for a competitor to rush up the inside.
How, then, are we supposed to find the best line? Some riders have that natural gift and are able to hone in on the quickest way around the track, all on their own. Typically, however, riders key off other riders for feedback: Last lap I didn't gain anything on the rider in front exiting this corner, but using a tighter entrance this lap I gained a few feet. Ergo, the tighter entry is quicker. The best line around the
track is almost a group decision, as riders measure themselves against each other lap after lap, day after day, and narrow down the options.
The one problem here is that quite often everyone uses a certain line through a section of track because, well, that's the way everyone does it. Riders new to the track are happy to follow along, and that well-worn line becomes a figurative (if not literal) rut. But the optimum line depends on a number of factors - the bike and its setup, the rider's level of ability, how defensive the line needs to be, and so on - and can change from weekend to weekend or even session to session. The key is experimentation, even if it seems counterintuitive: The quicker line in terms of time may be slower in terms of speed, or may call for restraint in one corner to make up time in the next.
At the track, we are constantly looking at GPS data to find that ideal line; by comparing segment times with the riding line for each lap, referring to onboard video, or even watching bikes go by on the track for a session, there are sometimes significant gains to be found in unexpected places.