Explanation of Double Apex??

I was following a fast Porsche into a high speed sweeper and since he's noticeably faster when he came up to me (before I let him by), I was like, what the heck, just copying his line and see how it worked... Scared myself a little bit, there's a time my front end keep pushing and I know exactly if I back up the throttle the rear end will come around quicker than I can say "shit". Not to mention I'm totally messing up the corner exit... and the porsche are long gone

So are you telling us how you got passed or are you asking for an explanation of what a double apex is, such as what the thread title states?

yes Both, Andy, I was telling you I was trying to follow a guy and almost lost it, and he told me he's double apex in that corner.

But I'm really not sure what's really double Apex... I suspect it's like you going in much tighter and let it track out a little as speed scrub off from the tires you going in for the second apex again thus you have way more room for WOT throttle?? Please tell me I'm wrong..

NSXDreamer2 said:

yes Both, Andy, I was telling you I was trying to follow a guy and almost lost it, and he told me he's double apex in that corner.

But I'm really not sure what's really double Apex... I suspect it's like you going in much tighter and let it track out a little as speed scrub off from the tires you going in for the second apex again thus you have way more room for WOT throttle?? Please tell me I'm wrong..

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Don't try following somebody if their line or speed is scaring you... your hands tend to follow what you see, but oftentimes you don't realize you won't make the turn till its too late.

If you want a good explanation on how to take different size radius turns efficiently, you should purchase the Skip Barber racing school book. You can order it from Amazon. It illustrates how you could make use of double apex line in certain types of turns. It usually depends on the radius and the characterstics of your car.

You probably need more seat time to be able to balance the car on the edge between over/understeer. Lifting gently or trail braking to tuck the front in should be a technique you get used to doing after some practice.



look at the image obove. turn 4 would be considered double apex as would 2. Some people take that line with a more agressive double apex, but this image was created to illustrate line options.

That's a great WSIR diagram of the Big Willow. I have my own that I made with notes and everything. You can't see it, but turn 2 is also a double apex corner. I never really considered turn 4 a double apex but really two corners since you go so straight mid-corner but I guess it really is.

I agree, read “Going Faster” to get the best explanation. A double apex line works by increasing both the corner entry speed and corner exit speed at the expense of the mid-corner speed. This is usually best for corners that have a significant amount of turning (~180 degrees). Although, a double apex can be detrimental for cars that don’t accelerate very fast because it relies on the driver to increase speed quickly from the slow mid-point of the curve to the exit. The NSX accelerates pretty quickly (except at high speeds), therefore a double apex may not be the fastest line on a very high speed corner. Just try different approaches and determine which line works best.

Bob

IMO, the term "double apex" is a bit of a misnomer. Here's why.

It's usually used for a long turn, which is treated as two turns - not in terms of apexes, but in terms of positioning the car. I'll use the line through turn 4 at Willow above as an example. Coming out of turn 3, you pass one "apex" when you come near the right edge of the pavement, and you track out to the left side. At the left edge of the pavement, you reach the sharpest part of the turn (smallest turning radius). After getting the car rotated is the second turn, in which you pass the second "apex" at the right edge of the pavement before tracking out to the left for the entrance to turn 5. Two turns, each with an "apex" on the right - hence the term "double apex".

However, this assumes the word "apex" is defined as the point at which you reach the edge of the pavement on the opposite side from where you enter the turn and exit the turn. The word "apex" can also be defined as the part of the turn that has the smallest turning radius (sharpest part of the turn), which means that it is the slowest point in the turn. Under this alternative definition, it's clear that this is actually a turn with only one apex, one point at which the turn is slowest, before which you brake, and from which you can accelerate out.

For another example of a turn which is often taken with a "double apex" - meaning, where you are at the opposite edge of the pavement - look at turn 8 at Putnam Park:



As you can see from the diagram, it's a 180 degree turn with a relatively constant radius. Some folks take it as a constant radius turn, while others use a "double apex" with a distinctly sharper point where they rotate the car midway through the turn, in order to straighten out (and quicken) the approach to that point and the exit from that point, as Bob mentions.

Hope that makes sense.

nsxtasy said:

Under this alternative definition, it's clear that this is actually a turn with only one apex, one point at which the turn is slowest, before which you brake, and from which you can accelerate out.

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I don't want to nitpick but turn 4 at Big Willow is more than approach, brake, turn, accelerate. You'd have to drive the corner to see what I mean. It goes uphill, peaks at the first apex, turns back downhill and turns again right into the setup for turn 5. I actually thought it was two turns, the first apex located at the top of the hill where you see the little rectangular grandstands to the left, and the first half of a downhill chicane where the second apex of turn 4 is located (turn 5 being the second half of the chicane). This explains why people couldn't understand why I was having so much problem with what I was calling turn 6 and why I was braking for it.

W said:

I don't want to nitpick but turn 4 at Big Willow is more than approach, brake, turn, accelerate.

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I have never driven Willow Springs and am only describing the line showing a "double apex turn" in the diagram. It's a good illustration of what folks refer to as a double apex. Don't get hung up on how the actual track is different; that's irrelevant to the discussion at hand. Any difference between the line in that diagram and the actual track is quite besides the point; the point is the principle shown in the example.