joey bagadonuts

I don't believe I ever questioned this aspect of the discussion. What I still don't see, however, is an advantage for the lower hp car resulting from a wider line. Is the ground lost at entry and the longer path made up by the faster apex speed?

Geo

Look, we can do this dance all you like, but you either don't read or remember very well. And my words absolutely DO NOT support this.

First of all, I posted a while back that I contacted my buddy who is a professional in the data acquisition field. He wrote much of the current software for Competition Data Systems (CDS) and now works with shock dynos and 7 post shaker rigs. He has clients from F1 on down. Ross Brawn called him in his office and he has been to the Toyota F1 team base in Germany as well as many Champ Car teams.

When I contacted him and asked about pro teams using the friction circle his response was, "Oh hell no. Professional teams expect their drivers to be on the limit, so they don't mess with that crap at all unless they think their driver has his head up his ***." Direct quote. I've cleaned it up and paraphrased it in the past, but basically reported the exact same thing.

Chris W., also a professional in motor racing in top professional circles told you basically the same thing.

The stop watch (in whatever configuration it may be) is still the yardstick. In evaluating drivers, teams will use plots showing may things during a run and compare them either with a teammate or with a previous session, but no where does FC come into play. Professional teams just don't mess with it.

You hear what you want to hear and forget the rest.

Secondly, as a practical matter, the FC is indeed simply a concept. No professional team has the time to accurately figure out exactly what the FC is. And how useful would it be to compare M. Schumacher's FC plot to say Andrea DeCrasherous (Michael's first teammate and generally considered a hack)? Each will have a hugely different limit. What can a team actually do with this information? It's trivia. Period. There are other more useful tools. Yes, the friction circle is real, but nobody really knows its true boundaries. So, from a practical point of view, it's simply a concept.

I hope you don't do engineering this way. You are looking at something and drawing a conclusion that meets your preconceived idea. A Nextel Cup car has hp not all that far off a F1 car and it will drive a hairpin much differently. It has less to do with hp than it does with the car's ability to turn and carry momentum. A Forumula Ford (talk about low power) will drive a line more similar to a F1 car than a Nextel Cup car. It's not about power, it's about the car's ability to turn and carry momentum.

JCP911S

Couple points.

First, Geo is correct. The driver drives the car at the limit based on skill, experience and feel. DAS allows the car to be tuned properly to increase the limit. When the driver goes back out and drives at the new limit, he's faster... so DAS makes him "faster" However, except inso far as the DAS demonstrate to the driver where he is not at the limit (e.g. coaching function with is certainly helpful in the real world), DAS does not make the driver "better".

Secondly..... All other things equal, the line with the apex closest to the geometric center of the turn is the "fastest" thorugh the turn.

To rephrase the discussion into practical terms, the driver takes the widest line (e.g. apex closest to geometric center) that allows WOT at the apex without breaking the tires loose. If the car won't take it, the driver keeps adjusting the apex later until the car will take WOT at the apex. If the car will take WOT and hold the geometric line, then he should take it.

joey bagadonuts

Very interesting, Bob. Just a few questions:

- Was the time lost due to the lower entry speed, longer braking and later apex offset by the exit speed gain? I think you'd need sector time to confirm this.

- Did you attempt to reduce the GT2's throttle oversteer with, say, a sway bar adjustment? It seems your '2' has a tendency towards oversteer. Wouldn't softening the rear bar improve the car's balance and allow you to put down more power sooner?

It seems you've compromised on your line choice and I'm wondering why you felt that was the best choice.

joey bagadonuts

This is classic line theory and I agree 100%. Most racers I know learn a track by doing a similar drill. They intially take the corners with a very late apex and keep moving the clipping point up until their exit line has them running out of road. As you stated, JCP, the goal is to get as close to the geometric line while at WOT.

If this puts an end to the low-hp/high-hp line debate, then so be it. It's just that CC stated that similar cars would take "very different lines" due to hp differences and I don't believe that to be accurate nor what you are saying.

Bob Rouleau

Joey - Great questions! The GT2 bars are set the same way as the GT3 one off full stiff front and rear. This is a compromise setting because I am loathe to fiddle with bars when it is raining. The GT2 does have the rear wing adjusted for more downforce - about 6 degrees greater angle of attack to help with the problem you described.

The turn in question is a high speed left hander and one of the few turns where I can accelerate hard before the apex, it is a broad sweeper. In the GT3 I go for a nearly geometric apex and as soon as I am lined up I squeeze on power - I am foot to the floor 100 yards before the apex. At the exit I am going about 185 KPH say 110 MPH or so.

If I take the same line in the GT2, I cannot use full power. After a couple of puckering experiences with countersteering at 125 MPH I tried a later apex. This results is a 3/10ths improvement in the segment time. The sweeper leads to a straight which is at about 1000 feet long so exit speed is important. I see an 10 MPH improvement in exit speed by taking the later apex. I agree that I am slower at turn in but the stop watch says the trade off is favorable. The entry point for this turn has the car going about 70 MPH and I (guessing here) suspect that I am losing about 5 MPH at turn-in because I chose the later apex. On the other hand I win 10 MPH carried fora much longer distance. That seems to account for the better segment time. The segment times and exist speeds were established by another instructor sitting beside me - no way would I be looking at the speedo in that corner!

Note that the ability to accelerate in the '2' is what sets it apart from the '3'. The corner is taken in 4th gear in the 2 (short shift to avoid hitting the rev limiter before track-out. In the 3 I can do it in 3rd (8200 RPM redline versus 6700). My GT2 is stock except for a Fabiani exhaust with race cats. It has close to 500 ft/lbs of torque versus 270 in the GT3. I figure that the torque difference is what makes the trade off favorable in terms of lap time. I think Sunday nailed it when he said that it is the HP/Grip ratio that counts. The 315's on the GT2 are not enough to accommodate the greater acceleration potential of the car.

I have also discovered that in the Carousel turn, the GT2 is faster using the double apex. If I use the single early (preferred because you can accelerate earlier) oversteer results from the early application of power. The double apex is a much shorter line (shorter distance) and using it shaves time off the segment. In the '3' the single early is faster.

From my experience, "the line" is indeed the line and can be driven by anyone in any sort of car. Certain cars will be able to go faster using a variation of "the line".

Unsaid so far is the fact that practical considerations also impact the theoretical "fastest line". Gearing is one of them. Certain cars will chose a line simply because it suits the gearing and results in a higher exit speed because it puts the engine in the meat of the power band. At any track gearing is a compromise and choices are made to minimize lap times or sometimes to give a car an advantage in sections of the track where passing is easy.

As a member of the profession myself, I would like to remind us what we were taught in Eng. School "Engineering is the art of intelligent compromise".

Regards,

JCP911S

Bob R.... I think your real world experience really backs up what we have been saying.... the torque difference between the 3 and the 2 is the telltale here.... you have to take a later apex to get all that power down... GT-2 always has the reputation of maybe a little too much power going through maybe too little tire.... a textbook example of our theoretical "high HP" car...now if you had a TT, is would be a totally different deal.

BTW, Bob, R... you need a GT-1... then you'd have a complete set... collect them all...

joey bagadonuts

Reminds me of the Kink at Road America. You can go into the corner pretty fast (100mph+) but you should give your self a little cushion. A late apex is also a good idea, here.
Sounds like you came up with the right answer. Thanks for sharing.

Bob Rouleau

Joey - thanks for making me think about it. In this and related threads I got my panties in a wad because if I have learned anything it's that there are few absolutes when it comes to driving.

With respect to the right line I will stick my head out and say,

The right line is the one that makes you go as fast as possible in your car under the prevailing conditions.

I think all good drivers start with the theoretical "line" and then adapt as necessary to go as fast as possible in their car on that day.

Chris (Premier) reminded us that we shouldn't get fixated on dogma. He (correctly) attacked the concept of braking in a straight line only. On the other hand I reject the dogma that trail braking is the right way to do every turn, especially in a 911. At the risk of making a bad pun, we should *color* this discussion in grey. There is no black and white here.

Rgds,

RJay

Just curious Bob, is the turn in question Six at Tremblant?

ColorChange

Joey, the S driver doesn’t want to take a wider, longer line, but he needs to in order to keep his speed as high as optimal (not normally as high as possible) through turn.

Geo:
Well, here is a direct quote from named and documented sources. F1 Racing magazine, September 2004, p 96 in an article on Mark Webber, “I look at what other drivers are doing and study my engineer’s comments. If I have to adjust the way I drive to be more competitive in one sector or another, then that’s no problem”. This is in direct contradiction to what you wrote, unless of course you consider Mark Webber to have his head up his ***. I sure don’t. Further evidence that the best drivers in the world work at their craft “I know what they are, I’m working on them.”

You are dead wrong, the same car DOES NOT have a huge different limit with different drivers. Furthermore, I do not have direct proof of F1 level fc analysis on a particular driver although I do have Ferrari’s data that shows they calculate them accurately. It is odd that they would calculate them accurately and record the data and not use it. I will try to get direct data/proof.

Also, Chris W uses the das for car set-up/optimization. He is not involved in driver analysis. I have asked if they have engineers that do that and he has not responded yet.

Again, you are dead wrong. The difference is primarily one of hp/weight ratio and lat g capability. There is a huge difference between 900hp/1000 lbs with huge lat g capability, and 700 hp/3000 lbs with poor lat g capability. This is why they take dramatically different lines.

JCP and Joey:
Your comments about the geometric apex is correct for the fastest speed through the corner, not the fastest time through the corner, and this is what counts. Your line description is dead wrong for high hp/weight cars, closer but still wrong for low hp/weight cars. Please read the Racecar Engineering articles I have been citing. I will be happy to e-mail them to you if you send me your e-mail address.

joey bagadonuts

What's the difference?

Bob Rouleau

RJay - Yes the sweeper is indeed T6.

Geo

And exactly where in this quote does it say they compare FC plots?

Nowhere.

It is yet another example of you hearing only what you want to hear. I have no idea how you get anything about FC plots from this quote and you conveniently ignore the fact that I already said (as did Chris W) that the ultimate tool used is the stopwatch in some form or another. There are other plots that are used for comparison. FC is trivia. But you don't want to hear that. You somehow contrive in your head exactly what you want to hear.

Each driver will have a different limit. The ultimate FC may be the same, but the limit each driver can take the car to will be different.

Yeah, get a copy of it next time Ross Brawn calls you in your office.

Well, while my buddy isn't directly involved in driver analysis, he is directly involved with those who are. I've already told you twice what he told me, but you choose to ignore that.

You're making this stuff up again, right?

ColorChange

Geo:
You are correct that I do not have direct evidence that they use g-g or fc analysis to coach their drivers. What this does is strongly discredit your unidentified source as he directly implied no one analyzes top drivers, when this is absolutely wrong at the highest levels. For another destruction of your unnamed sources credibility, F1 racing, May 2004, p 53, article about Alonso: The Driver “I discuss my telemetry and compare with Jarno’s. I look into what I can alter – braking a bit later, or not quite so hard, so that I can come into the turn a bit quicker. That sort of thing. That means I change the way I drive a bit.” Then again, maybe he has hid head up hid *** as well. One final point on this issue, you also do not have direct evidence that says they do not us fc analysis (yours is strictly hearsay). Mine is directly implied but not directly stated, so I will keep digging.

So, I have indisputable established that the best drivers in the world use something from their engineers (and DAS) to analyze their performance. Exactly what or how they do it is up to debate.

Yes! And the driver that uses more of the g capability of the car on the better line is the fastest. The g-g plot (or similar fc analysis like g-sum) shows part of that.


Poor reply. Your unnamed source has been heavily discredited, and you did not respond to my point, why do they do it then if it has no value?

Actually, no, it is the truth. What on earth makes you think it isn’t? OK, maybe F1 cars weight slightly more (can’t remember the exact min weight spec, I think 600 kg). But this is precisely the point, hp/weight and g capability heavily define the line.

Geo, maybe this would help. Since I have proven driver analysis does occur, please ask your friend what it is they are doing?