OK, but you are comparing the calculated G-sum with a theoretical max potential G-Force, which, although not an irrelevant calculation by any means, seems to me to be an indirect proxy for what is really going on. For example, I have heard that you get maximum braking traction at 30 degrees slip, but maximum turning traction at 7 degrees slip. If you measured directly the degree slip at any given time, you could better see how effective the driver is at modulating his or her traction at the limit (e.g., dancing at the edge), which may be far below the theoretical max potential G-Force at that moment, right?

 

Guess in a nutshell, G-Sum doesn't mean sh*t IMHO... maybe I'm old fashioned, but you have to systematically develope your driving technique and learn how to drive the car closer and closer to the limit... this means seat time and becomming both familiar and comfortable with how the car behaves... and how to control it in all situations.

As far as "friction circle" it is a useful model to help you visualize what the car is doing in a turn... but in the real world all it tells you is to manage transitions as smoothly as possible...

To use a football analogy, the "friction circle" is like telling a reciever "Accellerate as quickly as possible, make your cut cleanly, jump and the exact right moment and look the ball into your hands and catch it..." great advice... all you have to do it do it. and you are Jerry Rice.

 

I hear you, I hear you, believe it or not I do focus on seat time and driving . . .

 

TD, very good! Character AND a brain? In an attorney now? No way!

Guess what happens if you correctly manage your slip ratio under braking (usually 20-30 for optimal) and slip angle (usually 5-7%) during turning? Guess what measure you can use to show you’ve done it? You guessed it, you have maxed long g and lat g respectively. Now when you want to see how well the driver transitioned these forces, you look at g-sum. It’s that simple.

Admittedly you could argue that the track changes minutely, blah, blah, blah, but these minor effects are dwarfed by driver variability/error, for everyone I’ve seen including pro’s (but not F1/CART/IRL level guys because I haven’t seen the data). Boy would I love to see their data but I am highly confident that g-sum would tell tons, if only because it’s so hard to take a F1 car from -4.5 long g’s, to 3.0 lat g’s, to 1.5 long g’s in a typical turn.

 

You may be trying to state it as fact, but numerous times people who are professionals in the business and others who use DA regularly have chimed in and disagreed. It is not fact.

 

VERY well said.

 

If it helps you become a better driver... use whatever you want.... you can stare at graphs and G-Sums till your eyes bug out.... you still have to make it happen on the track...

My guess is you have to be pretty far up the driving foodchain to take DAS information and turn it into actual speed on the track.

So somebody tells me, a weekend tire squeeler, that I could brake 10 feet deeper and carry 3 more MPH into Deadman's Turn, I'd say "gee, thanks, right...all day long...uhuhh... phfffft!"

 

I'm not so sure I'd make this assertion that definitive. You're reminding me of a story related by Dennis Macchio (spelling?) whose the head of the Bertil Roos school. Sadly I can't remember the particulars of which driver, race series and which track, but Dennis was talking about his racing days and dealing with a fairly famous driver as a team mate. At a race on this track he noticed that he team mate was flat out in a particular corner that he was having to lift for. He resolved in practise to make it through, but couldn't. Not sure if he crashed or spun, in either case he simply couldn't pull it off despite them having largely identical equipment. He spoke with his team mate who told him that after the race he'd let him on his secret. The race run, his teammate having won the race, he revealed his edge.

The secret was something to the effect that during a track walk the teammate had noticed there was imperfection in the paving of that particular corner and if one moved off line the outside wheels would hook that impefection, the car would stay planted and be carried around the corner. In effect a bit of curbing to rely on. This enabled him to gain more grip than others who were taking the ideal line through the corner and it turned out to give him the edge to take the pole and go on to win the race...or so the story goes. Sadly, as Dennis related, the track was repaved before the next season, so he was never able to actually take advantage of that knowledge.

I wouldn't underestimate the abilities of professionals and skilled amatuers to seek out and find just those variables that you are suggesting we might as well ignore. Since hearing this lecture, in my own experience I've found a few of these place on several of the tracks I've visited where there is a bit more camber or a bump or groove that can be used to ones advantage. I frankly think that in the end, it is just this sort of thing that you are interested in, for its the way you really can achieve an advantage over those your competing against.

 

I started using a simple DA device in May for car setup. Fun at first. Segments showed where the most laptime was made up on clear laps and I did see improvements by throwing away a late braking effort to get early exit for the next small straightaway...etc. I find it useful, but it took 20-30 track sessions to apply it to my car/setup. One useful tool is the course plot comparison to a reference such as a club driver who podiums on every race in a similar car/class. You can map both your run and his/her(could happen) scaled by distance not time and directly correlate braking,g's, speed to develope some driving habit changes. eg: driver X carries 5mph higher at track out, but entry is 2mph slower. Does not take a math major to figure out what is going on.
Last: Segment times are very helpful and any decent DA system allows infinite dissecting of the lap,corners, straightaways. This allows you to dissect specific problems areas in driving, tire pressure/temps and suspension tuning.
Works for me at least.

 

Thanks for the laugh...

 

G sum gives a relative value from lap to lap.

If you are serious about analyzing your driving from data - use RPM, wheel speed, steering angle, brake pressure and throttle angle. Those things tell you what you are doing for various segments. Most people with Motecs are using G's for little more than track mapping.

In addition to the previously stated problems with G's, they also don't tell you things like, 'how smoothly did you release the brake or gas?'

Oh, and I have studied physics - actually dynamics and classical mechanics (in response to a previous question about someone's aptitude)

 

I am curious. Is there any pro team (meaning that the driver and the engineers are paid positions) that uses g-sum? I have not even seen the term used anywhere except this board.

 

Mark-

What are you using? (I assume rpm, b press, steer angle, throttle pos and wheel spd)

 

The list is long, so as better to confuse my poor self. MoTeC.

RPM, Speed, engine temps/pressures. Front and rear brake pressures, throttle, steering, 4 shock pots and 2 axis G.

The interesting math channels include calculated brake bias (this is actual clamping force using cylinder sizes), ride height and downforce (fron change in ride height) and center of pressure (from downforce).

I am also starting to play around with front vs. rear roll. I am wondering if I can see chassis flex/oscillation.

A lot is just interesting stuff such as seeing the difference in downforce when there is a tailwind. Actaully seeing how light the car gets over humps. The shock stuff is fascinating and I can see some patterns when the car is not handling the way I want, but I have yet to be able to make changes based on shock data - seat of the pants works far better for me. I am not the greatest suspension tuner, but I can tell the difference between fairly subtle changes and can recall entry/mid/exit characteristics. Have not made it to the level where I can really tune one corner of the car that is not right.

I have used the services of a pro (as in he was paid for many years to do that job) data engineer to help me understand how to use this stuff. I still need to hire him for a couple of days to help tune the car and coach the driver.

The most valuable thing I have ever done with data is overlay my traces with a faster driver in my car. I have never gotten any value from g data, corner radius, inverse corner radius or the deriviative of g's for smoothness.

Feel free to fire away with any other questions.

 

Very interesting. Particularly the downforce math channel calc. Are you able to make informed judgements about adjusting splitter/wing vs suspension based on the downforce feedback?

Have you ever found a good way to really measure slip angle (or even relative slip for that matter)? I was going to buy a yaw sensor and right before doing so was told they are a waste of money.

And, since you offered for me to fire away...

How difficult is it to tune you bump/rebound by analyzing the shock pot data. There is a good chance that I'll be running 2 way Ohlins next year and I am a bit nervous about setup. This last year I got myself messed up more than once putzing around with my shocks at races right up until qualifying. When I spoke with an engineer from Sachs he told me that if I did not have shock pots and a qualified engineer - I was merely groping in the dark. (Incidentally - last year car was 05 gt3 cup and next year car will be 997 cup)