Forgive me for what could be a naive question, but why does data acquisition and analysis focus on G-Sum and the friction circle so much?

My newbie impression is that great driving is largely about tire patch management. Specifically, you can only do as much as your tires let you do, but the difference between a good driver and a great driver is ensuring that you drive your car in a manner that optimizes what your tires will let you get away with, and then using, but not exceeding, those limits.

As such, why don't we acquire data on percentage slip, tire patch size for all four tires, tire temp, etc ?. . . You could then judge your driving (and car setup) on how well you used what was available to you under the actual conditions of the track at the time you took the data -- a great driver adapts to changing conditions, and this type of data seems like it might be better suited to measuring actual performance rather than merely comparing yourself against an assumed maximum g potential, particularly in light of the fact that every corner is different. I mean, I have a real hard time believing that the friction circle should actually be round (with the exception of the acceleration) as it is assumed to be . . .

What am I missing?

 

The real measure is lap times. Everything else is just *indicators* of driving well. When people start to focus on maximizing the indicators, instead of minimizing lap times, well, a lot of internet bandwidth gets wasted

The great thing about racing, like all competition, is that the people who think they have figured out a better mousetrap have the opportunity to go out and prove it in the field of competition. The ones who insist they have a better mousetrap, but can't prove it via podium finishes, are the *******. You'll recognize them easily...

 

You're not missing anything Todd. The friction circle is great theory and quite useful. But pro data acq folks don't spend any time on that stuff.

 

OK, cue ColorChange in....
Five, Four, Three, Two, One......

 

Yeah, let's hear from a pro...

 

G-Sum is a favorite on this board, but no where else that I have ever seen. My MoTeC does not use it, the professional data engineer that I got coaching from does not use it, nor do any of the amateur data folks that I have seen.

A significant problem with the concept is that you do not know what the g limit really is. It varies from corner to corner. Actually it varies at different parts of the corner. It varies from lap to lap. And if you have an aero car, it varies with speed and varies with wind speed. Anyone who thinks they know THE limit of their car, is not driving at the limit.

But I will share with you what the real aquisition is, and it ain't data. It is all about acquisition of trophies and checkered flags.

 

I use G-Sum only when I run out of Dim-Sum.

 

TD, How technical are you and how are your math skills? Have you ever had physics classes?

Lewis: I laughed.

 

hmmm

 

Personally, I find Segment times, Speed versus Lat G sufficient. For me, personally, G-Sum is a bit too abstract. An important thing to remember is that unless you're running a Magneti Marrelli F1 system and have a dozen or more engineers watching every aspect of yours and the cars performance, there are still a ton of variables that are simply far to difficult to quantify.

Traffic, track temp, ambient temp, tire pressure & heat, brake fade & sponginess of the pedal, your heart rate, body core tempature, hydration level etc. etc. etc. all conspire against you. A data logger isn't going to tell you where your were crabbing a turn, its only going to tell you how fast you got through it. In a case like this where you sneaking in too early and limiting your line, video is a better answer. Combine the two and maybe, if you spend a lot of time and think enough about whats going on and you'll be able to recognize how to get faster.

IMO, what we humans are constantly seeking is "The Easy Answer". G-Sum or any other measure is just that, a measure of a limited number of the factors involved that can't in the end tell you anything about the why or what to do to improve. Even if we suppose that G-Sum could tell you that you're using all of the car to some degree of accuracy, it tells you nothing about whether your doing the fastest lap possible. As we all know, just because we've used up everything the car has doesn't mean where on the right line, applied the brakes at the exactly correct spot, turned-in at the best possible moment. You can max out the car and still go considerably slower than you could.

As Sunday points in the end, lap times are the single best measure of your general performance. There is no easy answer as to how to improve. At my level, the addition of a DAS has been more about realizing just how much more ground I have to cover. For me, its really more of a dispassionate measure of where I'm at, as opposed to a tool to improve my driving. Yes, I've learned things abot my droving from it, but its no panacea. From me, its doing more days this year thats made me faster, the DAS helps confirm this. It simply reflects what I've done, and at least in this generation, isn't telling me in anything other than a general way (like be more consistent!) how to get better at it.

 

So true!!! To help illustrate Mark's point - here's what yer shooting for...


Personally in looking at my data and trying to go beyond speed and segment times, I try to look for smoothness in the raw data - key things like lateral G's, steering input, etc. Driver input and car response. I've found consistently (in the day job) that the car's working best when all the signals are moving smoothly, with no sudden harshness or jerk.

Dayum, I need to get with the pro data guys...

 

OK Guys. I actually didn't intend for this question to open up any of the old debates, and I wasn't trying to make a point here about anything else that has been going on in other threads. Believe it or not, I was just curious about the question I asked.

Since we have gotten a little off track, let me clarify where I stand on a few things.

I have in car video and a DL-1. I think that data acquisition and analysis is very interesting, and potentially very useful to certain drivers. At this point in my learning curve, I don't really bother trying to analyize the data I acquire. It is more of an interesting toy, unless I want to see what happened at a specific incident.

What am I doing right now at this stage of my learning curve? Rather than focusing on data, I am focusing on becoming a better "zen" like driver. Specifically, I think that, at a very general level, there are three components to becoming "one" with your car:

(1) accurately perceiving what your car is trying to tell you (aka "feeling the car" or having a "finely-tuned-arsemeter");
(2) having a full arsenal of car control skills; and
(3) having the judgment and experience to put it all together [subsconciously] in a manner best designed to make it around the track in the shortest time possible without damaging your car or anyone else's car.

I think that seat time, seat time, seat time is the best way to improve (1) and (3), and I try to spend as much time with instructors to work on (2). I am sure you could "discover" the car control skills and tricks on your own with enough time, but I imagine that instructors and professional coaches can get you there a lot more quickly. Once I have mastered (3), then I can imagine that data analysis would be very useful in shaving off those final seconds or verifying that certain lines actually are faster rather than the traditional lines. I am not there yet.

For a driver like me, data could create the same problems as "cones" do. Cones can be helpful when you are learning a new track, but they also create the temptation to "drive by numbers" rather than really driving your car. You start trying to connect the dots by hitting the turn in cone, hitting the apex cone, and then hitting the track out cone. As such, the cones can become a distraction that causes you to miss the forest for the trees. For me personally, I think that I could run into the same problem if I really tried to focus on the data too much in an effort to drive better, so I don't.

Rather than focusing on data, I am learning how to deal with the loss of ABS, more than half the HP I love so much (down to 158 from 325), and the loss of the PSM safety net. Once I learn how to drive the snot out of my n/a 944, I may reconsider my approach to data and/or move back up to a higher HP car, but that may take me a few years (or many). In the meantime, I am having a blast and that is all that really counts in my book.

I think video has been useful to me. Many times you "think" you are doing something or you think that you are not doing something (e.g., shuffle steering) because you don't intend to do it but you watch the video and it makes a liar out of you. The video -- and data -- can be a brutally honest way to correct misconceptions that you are having in the car. Also, video helps you "relive" your track time by seeing the same lap over and over and over.

Now, back to the topic. The idea that SundayDriver articulated was exactly why I started this thread. Also, I wanted to verify that I am not crazy by thinking that the only real purpose of the car, and thus the end goal for the driver, is to manage your tire patches (i.e., drive the car in a manner to optimize traction and use all available traction for the goal at hand). If that is true, then you would think that data acquisition would best be served by focusing directly on tire patch-related variables rather than on indirect proxies such as G-sums.

Tim, my undergraduate degree is in Architectural Engineering. I worked in the field for a while, but I moved to a new career before sitting for my PE license. Chances are, I will understand most technical explanations you throw my way . . .

TD

 

That's why I bolted a laptop into my car to calculate the optimum corner entry trajectory.

Data Acquision is a valuable diagnostic, but since the goal is going around the track faster than the other guy, laptime is the ONLY quant that matters.

Bottom line, you need to learn what the car feels like at the limit and drive it there 100% of the time. Use all the DAS and theory you want, but you still have to be able to DO IT in the car.... It boils down to hands, feet, eyes and butt-o-meter.

BTW... my car generates more Gs braking and cornering than it does accellerating, but I bet any racer will tell you their goal is to have their foot on the floor as long as possible..... maybe we should be maximizing "WOT-SUM"

 

JCP911S,

I bet you posted this before you read my last post . . .

I am trying hard to steer this thread away from the traditional debate about the usefulness of data. If you read my post, you will see that I personally don't disagree with what you are saying. I am just curious about the question I posted.

TD

 

TD:
The goal of the driver (non race conditions) is to complete a lap as fast as possible. If both cars drive the ideal line, the one who goes faster will have the lower lap time. This, by definition, means he had a higher g-sum around the track. In real terms, what does this roughly mean? It means brake as late and as hard as possible, turn with maximum lat g's, and accelerate as hard and as early as possible. G-sum plotted through the turns shows this perfectly, specifically, how well the driver trades braking g's, for lat g's, for accel g's.

G-Sum analysis is one of the best things you can do to evaluate driver performance. I do not state this as an opinion; I state it as a fact. If you want to look at my numerous posts and you have specific questions, I will be glad to help you. Once “the light goes on”, you will see the beauty in the approach.