Premier Motorsp

I am tired of sifting through 200 posts to find the first one I haven't read so we start up a new thread.

This 'line is the line' thing is just plain dumb. First we have to clarify that a deviation of a few feet is significant. Missing the apex by a few feet is a big deal right, so changing the line by a few feet is also a big deal.

Some real world examples that no one in their right mind can argue with:

Big-hp and low grip (Viper on street rubber) vs. low-hp and high grip (SRF, FF) in a 180 degree corner. This is not so uncommon, especially at the artificial road courses we have these days (Barber, Gingerman, that ilk). The Viper is not going to double apex, but is going to go for slow in fast out. The FF should double apex and apex the 2nd apex relatively early.

Really fast sweeper, same two cars. The Viper uses a normal line, and the FF misses the apex by 15 feet in order to minimize scrub since the turn is flat out.

Porsche with ABS, Porsche without ABS at Turn 17 at Sebring. The ABS car double apexes because it can turn in really early and brake over the super bumpy entrance. The non-ABS car turns in much later to stay on the smooth part of the straight.

I can go on and on but I don't think I need to.

Chris Cervelli
Premier Motorsports

JC in NY

Agree. While lines will be similar, the optimal line is a function of the chassis and grip situation on the four wheels. For instruction purposes we often talk about "the line" which is fine for a beginner, but in technical terms each chassis may have an optimal line that is different. This is plain engineering physics.

SundayDriver

Chris,

I'll bite. I am not familiar with the tracks you are using for examples. I am also not going to claim any absolutes on this. Let's leave aero out of this because that changes things dramatically. Here is what I was taught and have experienced:

At Mid Ohio, the instructors teach that the line is the line at Mid Ohio with only a couple of small exceptions on two corners. Now I have driven a 500+ HP TT on street tires there, tons of laps in an SRF and some in Hondas and a day in my Stohr. I agree with the instructors that the line is the line (with their couple of exceptions) at that track. If you could use an example at Mid Ohio, that would be great as that is where I have the most laps in the most types of cars and have the most professional coaching.

I have driven Grattan, Laguna Seca, Willow Springs and Laguna Seca in vastly different cars at each, and can not think of places where you want to change the line by more than my repeatability of about a foot. I have, OTOH, seen many places where I take a different line because of the way the suspension is reacting to bumps - T2 at Thunderhill comes to mind where I took a tight line in the SRF but a street car I instructed in was dancing all over the bumps and could not get any grip on that line.

The way I learned this aspect is that there are places you want to be WOT. In high HP cars (which is really the ratio of HP to grip, not absolute HP) you will have to lift somewhere in that sequence. You want the lift to be as early in the sequence as possible so you have to adjust what you do, in that case. One example is T15? (last corner onto the front straight) at Mid Ohio. High HP woule have to lift is they took the basic line taught there. The modification is to hole the apex for 3 or 4 feet so that you straighten T15 and take it flat.

Semantics - sheesh. When I tried to scan the thread on that issue, I got the distinct impression that Color was asserting that there were significant differences on most corners for HP. My experience and coaching strongly disagrees with that. Compared to significant changes on most corners, I would take the position that the line is the line. If you are suggesting that perhaps 10% of the corners we see need a 3-5 foot adjustment for high HP vs Low, then I would agree.

mitch236

I think this makes it ColorChange =one, most others =100

SundayDriver

I agree very much with that, though I think it is a different matter. The fact is, I can change the shock settings on my car and need a different line because of what the car is, or is not doing. That does not really address the theoretical concept of a different line for different HP cars.

ColorChange

Chris C:
I agree completely.

I will try to explain with words but can offer graphs if necessary. If you have two similar cars except for a huge difference in hp, the cars take very different lines. Lets assume car S (for slow) can only accel at 0.2 g’s. Car F can pull 1.0g’s in accel. In racing, long g’s are critically important and especially take precedence in high hp cars.

I hope that we can all agree that the fastest way through he turn is to stay on or nearest the friction circle, for any car.

Let’s assume the two cars enter a hairpin turn (followed by a long straight) at the exact same point, speed, and attitude. Car S wants to get through the turn while maintaining as much speed as possible because almost any speed lost cannot be recovered due to lack of power (a typical momentum car). So, S will take the more typical racing line, trail brake and turn down to the apex, hit max lat g’s at the apex (trying for near maximum corner speed, lets say 45 mph), and then accelerate as hard and early as possible. Because S only has 0.2 g’s pulling for accel, this leave all the rest for lat g’s (meaning he can go through the turn faster – carry more speed), and will take a wider arc. His entry arc will be wider as well.

Car F trail brakes heavy and deep, taking a line that goes much closer to the turn because he is going to have a much slower minimum corner speed and a tighter turn radius. F can give up the corner speed because he can gain it back with the throttle. So, F dives into the turn, slows the car to maybe 35 mph at the apex (max lat g’s), and then gets on the throttle hard all the way through track out. F’s line is much more like a V. Because F can accelerate so hard (and acceleration takes priority), with 1 full g for accel this leaves little for lat g’s and he has to be slower at the apex so that he can get on the throttle hard and early.

Major differences:
F’s distance is shorter than S’s.
S’s is a sweeping line, F’s is more V shaped.
F is much faster through entry.
S is much faster at the apex (very short time).
F is faster on the exit (due to the large accel capability).
The apex points are probably different. I would have to think about for which would be earlier or later (probably F would be earlier).

Mark: This is anything but semantics and I am most definitely asserting that. The differences are huge 5' or more is huge as is 10 mph, etc.

Mitch, are you saying this is the first time I have been right on a major battle and I have been wrong 100 other times? Please .. I hope not. If so, please support your views in another thread.

mitch236

Just a little levity. I don't take this stuff too seriously. I enjoy driving and while I'm stuck at work, I play here.

ColorChange

Mitch:
OK, I can take that but I hope you understand I'm a little overly sensitive at this point.

P.Po

Originally Posted by ColorChange
Mitch, are you saying this is the first time I have been right on a major battle and I have been wrong 100 other times? Please .. I hope not. If so, please support your views in another thread.

A measure of a man is the number of times he won an argument online. No, that can't be right... maybe it's how much alcohol he can drink?

I think the bottom line is nobody really cares who is right, let's just go to the race track and drive!!!

I wonder how G-Sum would work in Ice Racing? Hmmm.... Probably not at all. You guys should come out to Ontario, Canada and try this Ice Racing stuff.... you would really learn a lot about G-Sum. Or at least learn why it's not always usefull.....

-Patrick

smokey

Good explanation, CC. Very clear and logical, with no ad hominem bs. One suggestion: expunge certain words from your future posts - idiot, fool, liar, anyone with a brain could ... and you might have more fun and learn more. Driving is mostly eye/hand co-ordination, not IQ. Perhaps a slight shift on the arrogance/humility spectrum is indicated as well, but that's just a suggestion. As Seargeant Friday used to say, "Just the facts, ma'am..." Think of driving as learning to play the trumpet.

ColorChange

Smokey: I largely deserve that. OK.

Skip Wolfe

At Mid-Ohio there are definitely a couple of different lines that are taught. The school "safe" line and the race line. The most noticeable difference is going into Madness. The school line has you take an late apex on T6, come up nice and high into the top of Madness and take a late apex. This is still being taught by many instructors at PCA DE's. The "race" line taught by the Mid-Ohio instructors has one take a much earlier apex on T6, come into Madness fairly tight, and let the car drift out much more at the exit. Sort of tough to put it in words but those of you who have been at Mi-Ohio will know what I am referring to. So this isn't necessarily a different line for different car, rather a difference between schools of thought. So just because an instructor says that his line is "the" line, doesn't necessarily mean its true.

Jim Child

That's also the slow line. While it may be safer it there is absolutely no other reason to use it. All of the fast drivers and racers I know use the "race" line which you described very well. If I have a brand new student I'll teach both, explaining that one is slow and safe, and the other is the one the fast guys use. I'll then let them decide which one they prefer. If I have an intermediate student who is showing some speed and promise, then I'll strongly suggest they use the faster line.

JCP911S

CCs example of low HP vs High HP is essentially correct. All other things equal, the high HP car will take a "Late Apex" line aka "Slow in Fast Out". The low Hp car will max cornering speed with a more geometric center apex.

Compare the lines taken by fast 911 drivers and fast 944 drivers and you will definately see a different strategy as far as line selection in the same turns.... the driver adjusts the line to take advantage of the car's strenghts and minimize the weaknesses.

THese adjustments are fairly subtle, however. DE students need to be pretty advanced before they are ready to deal with stuff like this...I'd say a top Blue or even White level driver.

smokey

At Mosport, there is a similar difference between the DE line and the race line at Turn 9, for similar reasons. That's largely because DE and racing have completely different goals. There are many DE cars lapping Mosport faster than Stirling Moss did in winning the first major race there. The cars, especially the new ones, are very fast, and - let's not forget - one wrong move can be terminal, even with all our safety devices. The DE organizers take on a lot of responsibility, and want to keep it safe so that DE can continue with reasonable insurance rates, etc. In DE, roll cages, fire systems, harnesses, suits, and electrical cut-offs are not mandatory, so the stakes are different. Last year at Watkins Glen, I was passed a number of times by a very fast 996 TT, and waved him by whenever I saw him. The final time I let him past I came to the top of the esses, saw a cone on the track along with some dirt, and backed off. The TT was against the wall on the outside at the top of the esses, facing me, with the instructor looking back wide-eyed at the cars exiting the esses at about 120. If that car had stopped broadside across the track at the top of the esses instead of against the wall, the result would have been quite interesting. (Excuse this rant from a middling driver who just got his car back after an encounter with a spinning car at the entry to Turn 2 at Mosport.)