ProCoach

That is an assumption not supported by the data...

Veloce Raptor

Bingo

ProCoach

And that assumption IS supported by the data...

Slakker

So the different line for a SM vs say a 7Cup is based upon acceleration and not lateral grip? Or is the line really that different?

ProCoach

You are on to something! Nope, not that different... Ties into what Rob has said for thirty-five years.

Brian C in Az

If you consider the maximum grip of the tire as your limiting factor in corner speed and exit speed, you then realize that a low hp car can't use all the potential grip of the tire during acceleration, so you maximize that grip by maintaining more momentum and use as much of the tires' total grip as possible in the form of lateral grip. The tires' total grip (let's use 1.4 g) can not be exceeded, so we have to decide how we can make best use of it. A high hp car can exceed the tires' total grip during acceleration, so to maximize the power of the engine, we have to give up a little lateral grip to provide for more grip during acceleration. If you are cornering at 1.4 g then there is no grip left for applying your 500 hp to the wheels. Therefore, you try to use a little less lateral force through the corner exit in a high hp car by driving a line that gives you a slightly straighter exit. You can see that line on most F1 tracks develop during P3 and qualifying; look at the black rubber trails. Using less tire grip laterally gives you more available grip for acceleration. The Spec Miata on the other hand can barely reach .5g on acceleration, so we drive a slightly different line and maintain more momentum and apply power sooner after we drift through the apex as we try to use all the grip available to us.

AdamBrouillard

Yeah, the ideal apex is based on the acceleration potential of the car for a given corner and the resulting line will almost always fall somewhere between a circular exit and spiral shaped exit (a line with a continuously expanding radius). More acceleration potential needs a more spiral shaped line. The quick reference chart shows the common things that will affect the acceleration potential as well as the two typical ends of the spectrum. While the lines at the two ends of the spectrum look quite close to each other, the speeds can vary greatly. In the circular exit, the speed at the apex is the same as at exit, but the spiral shaped exit might have a corner exit speed more than double the apex speed.

So if we define a momentum car as one that goes to full throttle at the apex then just about any car does become a momentum car in higher gear corners because of low acceleration potential. And on the flipside, just about any car can also have a "high powered" type spiral exit if the corner is slow enough.

Thundermoose

Thank for explaining this concept.