How Does The Racing Line Work?

02 Sep 2015

This video describes the ideal geometric racing line, but that doesn’t necessary mean it’s the fastest line. This gets more complicated and depends on the vehicle, if it has more power it may be beneficial to hit a late apex to straighten out and take advantage of the fact that the vehicle can make up lost time with faster acceleration. Basics first though! :)

Comments

I have a question… we have a gokart track in my town thats about 1km Kong but the shorts way around it logged was somewhere around 850m. When do chose between speed and distance? Is there a golden rule for this or anything of the sort?
Oh, and my swedish autocorrect hates me…

Go for the shortest distance your kart can hold.

You pretty much always choose speed. Karting is all about carrying as much speed as possible through the corners. If you can come out of a corner at 50 km/h, you’ll hit a much higher speed and cover the distance of the straight much faster than if you came out of the corner at 40 km/h. The difference in distance is nowhere near enough to improve your lap time by taking the shortest route. Thats the reason we use racing lines.

So cool, it all makes sense when described like this! great visuals

Here is a little correction.The speed carried through a corner is independant from the mass of the vehicle. Therefore, here is a simpler equation:V = sqrt(G x r) V = sqrt(9.81 x 80) Source: I study physics.

That may be true in the idealized space in a physics class. However, in the real world, tires, suspension components, and other factors come into play to the point where yes the mass and specifically the height of the mass above the ground of the vehicle does factor in. Source: I am a civil engineer.

The bigger correction is that the ideal line is not a constant curve. It is a spiral curve that should slowly decrease in radius if you are trail-braking and should slowly increase back out to infinite radius (straight line) as you accelerate out of the curve. Just like you should be smooth with the brake and throttle input, you should also be smooth with the steering wheel and transition into and out of the corner. Having a constant radius would mean jerking the wheel to enter and exit the corner.

Because, SCIENCE!

(and bacon, lots of bacon….)

Engineering Explained never fails to impress. Great video!

So say it wasn’t a perfect 90 degree corner, like the infamous deals gap, or any real world corner, where would the apex be and how would you determine the line? I’ve been driving for 2 years and I want to get into the technical racing aspect, but my brain wants to overthink it, is it something that is felt on the track or something I just have to learn through experience?

First we have to remember we are talking about geometrical ideal line,not the practical line…you would always be lookin to fit the biggest radius circumference, barely touching the apex like shown on the video. The apex would theoretically be determined by that radius. In case of a double apex you would be fitting two circumferences and if one is tighter than the other, those 2 would have a different ideal radius, so you would be mixing them, trying to find a combination where the result would bring a single circumference, even if you dont get to touch one of the apex. I personally dont do math to find this while im driving around, I learn it by goign through that corner once and again, till I find the line that will allow me the highest cornering speed and exit. Rough example (the middle section with double apex to the right) ; www.youtube.com/watch?v=McurxXUrMMg

You have to learn it. Thats why practicing on a circuit before you race there is so crucial. It takes a great deal of practice to figure out the best way through a corner and different drivers with different cars might end up taking 2 very different lines through a corner but be just as fast as one another.

You REALLY don’t need the math to know all this. And if you DO need the math then you shouldn’t be driving around corners at speed.

This is why I love racing so much, it (can) take 2 of my favorite things, physics (real life math) and cars (Brapbrapbrap) and combine them in one harmonious symphony filled with geometry AND noises of beautifully aggressive engine screams.