Q: “Following on from Podcast 61 with Ann Morey in which she talked about drawing arcs on track maps to work out ‘the line’, I tried a similar thing for my local kart circuit. The corner I picked is a combination of two fast clockwise corners that need to be treated as one. I plotted the largest diameter circle I could that joined the following three points: 1) the outside edge of the track at turn-in; 2) the apex/clipping point; 3) the outside edge of the track at track out. I also superimposed three karts onto the circuit at these three points. This corner sequence is preceded and followed by decent length straights so I see no obvious reason to compromise/prioritize entry or exit over one another. My question is this: Why is this theoretical line not the fastest, and if it is, why do people not tend to drive it? I see people make roughly that clipping point and that track out, but I don’t see many/any people turning in that late and missing the first apex by that far.”
A: With the limited information that I have, here are a couple of possible answers to your question (which is very interesting):
- The line that has the most grip usually is faster than the theoretically ideal line. So if everyone takes a more shallow line entering the corner, it will likely have more rubber down there, and therefore have more grip. And grip usually wins (but not always).
- Looking at the arc you’ve drawn, it does add distance to the track. Often, a shorter distance – even if the line is not as “ideal” – will result in less time taken to get from one point on the track (the start line) to another (the finish line). This seems to be more important in lower-powered cars (like karts). If you watch NASCAR Trucks run at Daytona they take a completely different line than the Cup cars do – they just drive around the bottom of the track. That’s the shortest distance, and since they don’t have the same higher power/speed that the Cup cars have, they don’t need to use all the track.
So if I had to guess why drivers don’t drive the line you’re drawn, I going with grip and distance as the two likely reasons. Usually, given enough time, at least one driver will try a different line and find out of it’s faster. If it is, others will follow. So I suspect that someone has tried the line you’re drawn and found that it’s not as fast.
There are always exceptions to the rules…