Fastest way around a track U-Turn?

out - in - out
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I'd need to see a photo or diagram of the turn

Big Bend at Lime Rock is a very wide U turn, almost like it has a 50 ft straight in the middle

While Moroso or PBIR has 2 U turns, 1 like Big Bend and the last corner is a tighter u turn

at Big Bend in the middle you can get off the gas for a 1/4 second which allows the car to rotate then punch it on the way out

top photo is PBIR
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Sareve,
What Lennard used as a U-turn type of turn was a constant radius turn and while one could use the line shown in his diagram, it won't be optimal and one would suffer some of the symptoms you describe.

It'd be better in your T4 @ Phillips example to drive in deeper, wait later for turn-in, turn in steeper while carrying some brakes into the turn, apex later in the turn itself, unwinding the wheel sooner - perhaps even before reaching the apex, allowing you to get on the throttle sooner and thereby make the following straight longer on exit. No mistake about it, T4 there is a slow-in, fast-out turn.

Apexing the turn earlier, say at the geometric apex point is going to be slower overall as you will run out of pavement on exit, or have to stay slow for longer in the turn to avoid doing so. This is the benefit of a late apex and the case you present is pretty much textbook.

Speaking of textbook, I'll use this image taken from the Ross Bentley book Speed Secrets (http://astore.amazon.com/wwwrelation01-20/detail/0760305188/180-0918745-9981255) (indeed, with permission granted ) to demonstrate. The comments in red in the image are mine and perhaps slightly off/beyond topic - sorry, I just grabbed it out of my classroom presentation stash...

Hope this helps!

Cheers & C U @ d'Track!!
C

Chuck Hawks,
Facilitator, Pro-Driver, Instructor & Coach
DreamsFulfilled, LLC & rEvolution Performance Driving System ©
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You are no doubt much more qualified than me and hope that you will comment on my comments.

I agree with your "going deep" approach if the car has good acceleration and the straight following the corner is of a reasonable length. You are sacrificing entry speed for exit. However, if you are in a relatively modestly powered car the "going deep" will result in a sharper corner with a lower minimum speed. It may then be advantageous to use a normal mid-apex and try to carry more speed from turn-in to apex. A late apex as you suggest is not always the fastest way around on a symetrical hairpin.

DM18
Amateur Driver, Bad Student
DM18 Slow Driving System

 

DM18,
Agreed on the differences between high HP & torque cars vs. low but this is more about how soon one can get on the throttle. The exit of the corner is more important than the entrance - albeit the object truly is fast in, faster out - we usually defer to slow in, fast out... or "in like a lamb, out like a lion."

A more symmetrical apex line may indeed allow you to carry more speed into the corner but will likely also delay application of the throttle much longer and make the progression to full throttle much longer as well. Given all this being said, I will not say 'never' or 'always' in this or many contexts. There are exceptions to most rules and that means that there are some turns where a momentum car would benefit more from a more symmetrical line just as you postulate.

In this case though, Sareve was referring specifically to Turn 4 at Phillips Island, which is not a symmetrical turn. It is certainly a prime example of the origin of slow in, fast out. Even the superbikes need to reduce to 1st gear to properly navigate this beast - and yet, immediately after initiation, this turn opens up progressively, punishing a symmetrical apex approach. Check out the turn and I think you'll see what I mean. (pic below)

Driving this type of turn deeper such that one can unwind the wheel sooner, and thus get on the power sooner/more aggressively in turn makes the effective straight between T4 and T5 longer and therefore we stay on the power longer. Also keep in mind that we're not talking about moving the turn-in and apex points by hundreds of feet here, more like 20-40 feet (3-9 meters).

I hope this makes sense and isn't muddying the water more than clearing it.

Cheers & C U @ d'Track!!
C

Chuck Hawks,
Facilitator, Pro-Driver, Instructor & Coach
DreamsFulfilled, LLC & rEvolution Performance Driving System ©
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i'd do as Chuck's diagram states. Excellent post!