Autocross Line Question

wbjones wrote: mainly you need to experiment ... more often than not tighter IS quicker ...

This. I should have mentioned that in my post as well. Don't drive from cone to cone, but keeping a tight line is usually faster, especially if it's a dusty lot (dirt and debris will get blown to the outside line). You have to be going significantly faster on a wide line to make up the difference in course length compared to a tight line. Autocross courses are so short that it's hard to make up that ground. I learned that the hard way at nationals last year by approaching the faster course with wide lines and it certainly didn't work.

At 45mph you are traveling at 66 feet per second. Any added feet to your driving line adds time, and must then offset that time by being much faster.

I think the black line looks pretty nice and tight..

I have to second the "have fun" part, and also add to be more concerned with the learning than the speed. Sure, winning is fun, but learning how to control my car near, at, and even slightly over the limit is the best thing that I've taken from autocross. I've had situations where autocross has literally kept me from crashing a car, and it didn't even get my heart rate up. There's no other motorsport that throws so much at you all at once, so when you can do that with a sense of normality, then you're way more prepared all sorts of accident avoidance.

Let's get a little physics-y. This is why the shortest line is most always the fastest:

F=ma. In the case of turning a vehicle (lets use a 180* constant radius bend in this example), the mass of the vehicle is constant, and the maximum turning force - and therefore acceleration - the vehicle is able to develop is assumed constant, regardless of radius of turn (I guess this may not be perfectly true, due to imperfect ackermann or something, but it should be close). Let's assume that acceleration is about 1 G (which for most cars it is).

so then, f/m = a = v^2/r. v = meter/sec, meter = (pie)r (half the circumference of a circle - 180 degree turn).

Pull it all together: a = ((pie)r/sec)^2/r

Solve for sec: sec = (pie)r/root(ar)

If a is indeed 1, or close to 1 G (1 G = 9.8 m/s^2): sec (almost equals) root(r)

Or in looser terms, as radius goes up, so do the seconds.

In reply to Robbie:

not always ... usually, but not always ... I lost an event, I think it was yr before last, because I continually forced myself to take one particular turn tight ... I always clipped the cone, (2 sec penalty) .... finally one of our pro drivers (an Evo School instructor) asked me why I kept trying to tighten up the corner ?

watched the pro drivers in the next heat ( I was the starter and had a clear view of them) they all pushed out on corner entry and made a longer straight out of the exit that I would have had even if I'd managed to leave the cone standing

but WAY MORE often than not, tight is quicker

In reply to wbjones:

Makes sense, that in certain cases (like entering a long straight) where extra mph is worth the extra time it takes during the turn because you carry that extra mph down the whole straight and may gain more time back.

Now also of course it was only a mathematical example, and like all physics and economics, is 'while everything else is equal', which of course, in real life all else is never equal.

Overall though we are saying the same thing, "tighter is faster, usually".

Just gonna leave this here...

https://www.youtube.com/watch?v=Z8iPiPn7a6E

That's my best run of the day. Feedback welcome.

not bad ... would like to be able to see some other runs with more experienced drivers, with cars similar to yours to use as comparison ... but looked like a fun course ...

hope you had fun, regardless of how you felt about your runs

In reply to c0rbin9:

Next time put the camera somewhere else. Either further back so you can see your hands and steering inputs, or outside the car so you can see proximity to key cones and get a better idea of the line driven. It's really hard to offer feedback from a video like that other than "yep...you're on course...OK then."

this thread was revived by a canoe, paddle at your own risk