Bob Rouleau

Claude Shannon (one of my heroes) said "never discard any information until you have extracted everything you can from it. DAS is good. When used by a coach it can speed the learning process. I am not amongst the "useless info" crowd. On the other hand using DAS by yourself to try and improve your driving is a little like trying to remove your own appendix. It can be done but a surgeon does a better and safer job of it.

Cheers

Geo

Bob, I don't think anyone is saying DA is useless despite CC's spin. What is hotly debated regarding DA is the value of a gg plot. DA is tremendously useful. In the right hands.

ColorChange

Pesky, OK, we're in general agreement and as I have said over and over again, I do plan to use instructors, regularly.

ZBlue: Agreed.

Bob Rouleau

CC more later I am busy reading "Trail Braking - and engineer's guide"

ColorChange

OK Bob, ... I'm not familiar with the text. Can you give me reference?

Premier Motorsp

A few points in CC's defense. As usual, there is underlying truth in what he says.

If you are a religious person, you can imagine God himself driving a car. His best lap will represent the capability of the car. Now you get in, and you will run a slower lap, right? The car's capability did not change, the driver's did.

What is so hard to understand about this?


I happen to agree with M758 that the steady-state capability is pretty much useless. (more on this below) Everything important happens in a transient, as Larry and others have pointed out. (it is ironic that Larry brought this up, since even though he is totally correct, he negates his anti-trail braking stance by admitting that weight transfer, properly used, is the key to the whole thing)

I'll bet that CC is thinking this way:

The car is capable of a certain lap time. Right now I (CC) am running this lap time plus X.XX seconds. In order to improve my lap time, I need to know at which points of the lap I am slower than optimum. In order to determine which points of the lap I am slower, I will study my g-sum data and compare it against what I believe to be optimum.

I don't think anyone can say this approach does not make sense. It isn't 100% practical since everyone agrees that track conditions are going to make wide variations in the best possible g-sum. Also there is the whole line thing.

But even with these limitations, maybe CC feels that this approach is better (or maybe just more interesting) than riding with an instructor. I can't fault him for that.

To Bob R and Larry:

The GT3 is the best trail-braking car ever. I will bet my life that either of you guys will knock .5 seconds off your best time at the track of your choice if you make a serious effort to increase your entry speed and brake all the way to the throttle application point. You will probably need a sway bar adjustment to get the full effect if your cars are set up currently for slow-in, fast-out. Try adding understeer and then trail braking to cancel the understeer and you will be faster.

Skid pad testing:

You can meaningfully test non-weight-transfer settings on a skid pad. Mostly this means camber and tire pressure, compound etc.

Chris Cervelli
Premier Motorsports

Bob Rouleau

CC - it's the August issue of Race Car Engineering an article by Zapletal who applies a different approach to the analysis Mitchell did. This one is a lot simpler. He shows the benefit of parabolic and eliptical lines as opposed to the classic line for certain corners. This has been discussed in earlier threads, it's taken me this long to find a copy of the magazine. Interesting reading.

Chris - I will experiment with a softer rear sway bar. I closely observed my cornering techniques and I trail braked for rotation, really fast corners called for a simple lift to rotate then it was back to power. One corner which fits your theory is tough because with my present setup, the biggest moment of instability is right at turn-in. To carry speed you need a very soft release of the brakes and a fast move of the foot to the gas to balance the car. The exit is a decent straight so exit speed is important. I will experiment with trail braking and a much earlier (and gentler) turn in and report in about ten days. One of the turns I do trail brake into is a carousel and I use a parabolic line exactly as described in the Racecar article - so I am not a complete Luddite.

ColorChange

Chris: I really enjoy your posts for their fresh breath of truth in an otherwise too often smoke filled, stale smelling bar that makes me choke and my eyes burn from some of the patrons.

My personal approach is to learn as much as possible with heavily limited track time. I do this by trying to master the subject technically, and then trying to use this insight to make my limited track time as efficient a learning experience as possible. This is where the DAS comes in. This does not leave time to explain to some instructors that slow in fast out, don’t trail brake, etc. is BS for me, IMO. And since none of you here know me and have tried to instruct me, you can’t rationally dispute my opinoin, you can only express your opinion. So, I will be a little selective in my choice of instructors, but I will use a good one as much as possible. Specifically, I am now trying to learn how to drive my new car, especially how to handle my car near the limit (driver induced or not). Once I have this, I will be much safer and then can more confidently concentrate on set-up, trail braking, lines, g-sum, etc.

I couldn’t agree more on recommending way more trail braking. DAS would show their inadequacies as clear as a bell. I wonder if that’s why so many object to it so heavily, and with no factual justification for their reticence?

On the skid pad issue we disagree. I believe you can look at transients extremely well by setting up a turn with cones. Approach the cones in a straight line, threshold brake, turn in and trail brake, neutral throttle and accel. This can be done, easily, is repeatable, and has extremely good value. You have just modeled a flat track turn (gee … much like most turns at Gingerman .. hmmm). You are correct if you only do the spinning around in circles most people do (and I am sure that is what you meant), but as you point out, this is only best for basic car setup (which is still quite valuable, especially if you can run different diameter circles).

ColorChange

Bob, do you dispute anything in that article? Have I said anything that conflicts with that article? I have both articles scanned and would be happy to e-mail them to you.

Finally, you have expensive cars, you can surely afford a damn $2k DAS. Take yourself from opinion, anecdote, and just pain BS to COLD HARD FACTS AND TRUE KNOWLEDGE! Your driving will improve immensely, and you will never look back if you have the technical ability to utilize it, and oddly enough, I think you do.

Z-man

Maybe I DON'T WANT NO STINKIN' DAS IN MY CAR!
CC: Why don't you take yourself from textbook logic, non-baseline data, and just plain ignorance of real world experiences and get yourself an instructor and LEARN TO DRIVE.

When the Green flag drops, the BS stops. Stick THAT up yer' DAS!

[rant mode]
I really don't understand why you stick around here CC: you refuse to listen to the experts (I myself am NOT an expert, but others here are), and you continue to make feeble attempts to prove your point, and get frustrated when those who have far more experiece (REAL LIFE EXPERIENCE) disagree with you. Are you expecting us all to one day show up at your doorstep wearing white robes and chanting "I belong to the church of the Color Change. May your g-sums be always at the max?!? " I truly don't get it.

But I also don't understand people who like electro-shock therapy. I myself don't find it to be too pleasant...
[/rant mode]

Happy trails,
-Z.

Larry Herman

Thanks Chris. In medium speed turns, I typically do that; trail the brakes into the corner as I turn-in, and then right back on the power. This usually occurs in the first 1/3 of the turn, well before the apex. Are you suggesting that I trail in farther? I feel like I am already at the limit of the grip of the front of the car when I turn-in. How can I carry even more speed? If I take an earlier apex, it feels really slow at mid-corner and like I am getting back on the gas really late. BTW my many years with the Carrera have given me lots of practice with an understeering car.

Bob Rouleau

CC - I don't dispute the article. The fact that I use parabolic or elliptical lines in certain corners is reassuring. I am still thinking about his theory though. His hypothetical car can accelerate equally in all directions, i.e. 1.0 G braking, cornering and acceleration. Under those circumstances it makes sense to trade off speed at the apex in favor of early acceleration. My car does not accelerate at anything near 1.0 G, consequently the trade off shifts back towards apex speed.
This comes back to the different lines for different cars based on power/weight/grip ratios.

I think you agreed in an earlier thread that a lower powered car would benefit from a 'classic line' with the maximum radius since it cannot accelerate hard out of the corner. John (Redline) is probably flat in certain corners with 1.0 G grip and 0.1 G acceleration. I have seen this myself since my GT2 lines are different from those of the GT3 in certain corners.

I fiddled with the math a bit (a pain without matlab) and I half way convinced myself that there is potential for a more general theory which generates a curve based on the ratio of lateral acceleration (cornering) to acceleration. As the ratio of Lat to Long approaches 1.0 the ellipse (or parabola for 180 degree corners) is favored and as the ratio decreases the ideal line tends towards the cosine.

At some point I stopped and decided it was time for a martini. I left myself with the thought that we do this instinctively - we all trail brake for slow corners. Is this because any of our cars is capable of good acceleration out of a slow corner, even a 944 with lower HP? My ability to accelerate is greater at 30 MPH that it is at 125 MPH. This at least explains why I take corners on our home track the way I do.

Finally, I can afford a DAS but I remain convinced that segment times are a better indication of success or failure when I experiment with a new line. That's how I intend to test Chris' theory of adding understeer to allow more trail braking. Seen from another perspective, catching the guy in front is a better indication of success and way more fun than analyzing GG plots. That's only me of course and our definition of what is 'fun' will vary.

Rgds,

ColorChange

Bob:
You still owe me an apology but I am going to respond to your post anyway. Your analysis is 100% correct and shows you have insight. The higher the accel capability (hp/weight ratio), the more parabolic/hyperbolic the line. Based upon what you wrote, you can easily handle DAS analysis.

You are correct, even with the DAS, you use segment times. But, there are two components to a fast segment time: line and g-sum. Without a DAS, you can’t tell if you drove a worse line at a higher g-sum, or a better line at a poorer g-sum. This will clearly show if you are trail braking enough and on the accel properly. Once you get to this level of analysis, you can dig deeper, into steering angle as a function of lat g and see if you are inducing understeer on entry, using throttle to balance the car, etc. All the balance things you like so much (rightfully so) are measurable.

Carrera51

Zman:
You have just coined the best line of the year. "Stick that up yer DAS." HA HA HA!!!

No one is disputing the usefulness of DAS. The problem CC is that you appear to be attempting to short cut the learning process by substituting DAS for instruction. If computer simulations and data were all it took to make us competent drivers, then we could have saved a ton of money, by buying some books and a PS2, mastering those, then going straight to club racing.

Part of driving on the track is feel. Feel comes from experience (doing it a bounch of times). I guess my DAS is comprised of the following :the seat of my pants, my eyes, my hands, my ears. I can tell when I have turned a good lap by how the car feels.

Sure a real DAS like you have would be beneficial to me and would help me shave a 10th or 2 here and there, but I would rather spend my money club racing. I've recently gone back and watched the in car video from my first race and compared it to my last. Like night and day. I attribute that to seat time, not science. Don't get me wrong, I am not discounting the usefulness of DAS. All I am saying is that in the early stages of this madness (track driving) there are more important things to concentrate on.

ColorChange

Mark:
I plan to COMBINE the two, good instructors and DAS analysis. I have said this from the beginning. I agree with feel and experience being critical.

Sadly, you and many others who have no direct knowledge and experience using a DAS think they can assess how much a DAS can or can't help. You can't do this because you have no (or little) knowledge to make an informed assessment. I do have the direct knowledge and experience and know it is a wonderfully powerful tool provided you have the technical orientation and capability to utilize it (it definitely isn’t for everyone). No, it does not replace instruction or experience, but it definitely allows ME to learn better and faster, and again, no one can dispute that statement as none of you either know me or have instructed me and observed my rate of improvement.