Any Data Gurus out there? Data from VIR

[TD in DC]

I don't have any video yet because I left my camcorder cable in my car (it is at the bodyshop now), but I do have data from VIR for those of you who are interested in that sort of thing. I know it is not as exciting as video.

I drive a n/a 944 with a suspension that has not been tuned very well yet.

The redline shows a 2:26 VIR lap from April, and the blackline shows a 2:27 VIR lap from last weekend.

OK, here is an explanation of what this shows for those of you who are data challenged.

At the end of the back straight, I hit between 113-115 mph, which I believe is about all my car has in it. In the braking zone, I am braking with a force of -0.8G, and then I pull a lateral G of about 1.0 into that first right-hander at about 43 mph.

Through roller coaster, I manage to get back up to about 85 mph, until I reach a slowest point of about 63 mph through hogpen pulling 1.1G through that turn.

On the front straight, I again reach about 113-115 so I am tapped out.

At T1, I brake with a force of -1.0G down to about 43 mph with a lateral G of about 1.0.

I take T3 at about 55 mph and pull a 1.1 lateral G.

At T4, I manage 1.1 lateral G at about 43 mph.

I know that I am at the hairy edge through snake, and the data backs that up by showing about 1.2 G. Yikes.

I manage to hit about 105 mph at the exit of the climbing esses (any more speed to be gained here will be through not scrubbing, because I am on full throttle from T4 all the way through).

At Southbend, I brake to about 87 mph and take it at 1.2 G. Yikes.

I am fairly happy with the amount of speed I carry from Southbend through to Oaktree. I brake only the amount necessary to downshift to redline at 3rd right before the turn in for the kink, and you can see that I don't accelerate very much between the kink and oaktree, which probably means that I am not overbraking "too" much before the kink. What the hell do I know.

At Oaktree, I pull about 0.9 G and take it at 39 mph.

Anyway, it is interesting.

For those of you trying to interpret the graphs, Each "tic" on the top mph graph is 8 mph.

Each tic on the lateral G graph, which is the second graph, is about 0.4 G.

I don't pay attention to the third graph, because I am not really certain what to do with "time slip"

Each tic on the bottom braking (longitudinal G) graph is about 0.2 G (I don't pay attention to the acceleration portion of the graph as it is too depressing).

As a disclaimer, I am getting my values by looking at the graph rather than getting the values from the data directly. So, there can be a margin of error. I am not so concerned with "exact" values, but rather trends . . .

When I look at the data, it looks to me like I am not getting off the brakes as smoothly as I should (it should be peaky and "sharp" on the way in, and rounded or "soft" on the way out, or so I think).

I would also think that I am still overbraking since I am able to get on the gas immediately upon turn in everywhere. However, I seem to be pulling decent lateral Gs, so I don't really know what to make of that . . .

Is anyone here good at analyzing DL-1 data? Please let me know and I can e-mail you the data files. I would be interested in any insights you could give me.

[TD in DC]

Here is a clearer (hopefully) picture of the data ( but this image is not labeled).



Looking at the data a little more, it seems that now I am braking later and more crisply, but that I am still letting up on the brake too much during the downshift (I do heel/toe). It doesn't feel bad in the car, but it looks bad on the data. It that normal? Am I letting up too much? Also, should the data show a more gradual easing of brake pressure when I let off the brake (e.g., a more gentle curve at brake release)?

Also, I am a little shocked at how much speed you burn off even when you just tap the brakes. Check out the speed drops in the two brake taps I do at the right and left apexes in roller coaster right before hogpen. Brakes are evil!!!!!

Finally, why are the lateral G lines not smoother? Is that just a function of the dirtiness of the data? It is not as if I am sawing the wheel or anything.

[TD in DC]

For those of you who have never been to VIR, here is a track map. We were running the full course (which includes only the full outside of the track), and the track runs clockwise.



The data clip I show starts at the track out of oak tree, which is at the very bottom of the map.

[TD in DC]

None of you guys play with data? For the most part, I can't make heads nor tails of it, but I hear you can really tell a lot if you know what you are doing. Thanks in advance.

[924RACR]

OK, as requested... sorry I missed the thread earlier!

Yeah, you're showing the overbraking you feared in most every corner. Hogpen seems to be carried much smoother and as desired (U or bowl shape) in the black line - you probably gained .1-.2s I'd guess vs. the red line. You also braked more decisively for the end of the back straight, and this also gained you a little time, maybe as much as .1s.

However you lost time to the red line all the way down the front straight. This is because your exit speed was slightly slower than the red line; you must have slid it on the corner exit, didn't get on the gas as early. You need to find that happy point where you can get on the gas as early, but carry all that apex speed. That is likely suspension tuning. Did/does your car get loose on corner exit? This might be why you over-slow; if you can't put the power down without the back getting too loose, you need to get it a little more stable. You need to be able to put down the power at the apex or a little earlier, but without having to have a lazy corner entrance.

I also notice in the black trace you really lost time halfway through the front straight - did you shift where you did not in the red trace? I see the drop in speed often associated with a shift, but only in the black trace. Need more info.

T1 you entered better in the red trace (I think it's the red trace), showing more of the bowl shape. Same deal in T3, but smoother entry in the black trace. T4 is just sawtooth in either trace, not so great (overbraked). Looks like you're doing well in 5, not much more than a lift required and it doesn't seem to be disturbing your accel trace much.

South Bend doesn't look bad - looks like you're carrying some good speed through and out of the apex. I'd suggest trying a gentle squeeze of the brakes to try to set the car up for the apex.

One lap your did a good job it seems through 11/Kink, trace is rather flat, but can't tell which one it is. Still want to try to find more apex speed in Oak Tree.

That's about all I can really give from these traces...

[TD in DC]

Thanks Vaughan.

I "think" that a lot of the difference in overall speed can be attributed to temperature differences. The "red" trace was while the track was at about 40-50 degrees F, which is nearly ideal. The black trace was when the track was about 90-95 degrees F.

I actually think I was probably driving better in the black trace than the red trace. I "think" that my exit speed was the same or better in most of the black trace corners (I will go back and doublecheck, but you can see it more easily in the lower, unlabled graph), but I think my 147 horses were having to work much, much harder in the higher temps.

And yes, my car oversteers unless I am on the gas so I use the gas pedal to keep the car settled. I am in the process of getting a new suspension, so we shall see what that allows me to do . . . .

[924RACR]

Agreed; overall the black trace tends to show better driving technique - but still with room for improvement.

Re: suspension - where are you now and what are you going to? Steady-state cornering your car will oversteer? Doesn't sound helpful...

[924RACR]

Another thing - does your data analysis SW have, as mine does, the ability to graphically compare the two laps and show where you're gaining vs. losing speed? That's really what you need here.

If not, see about exporting to Excel the ET on the lap vs. distance, take the difference, and plot.

[TD in DC]

Originally posted by 924RACR
Agreed; overall the black trace tends to show better driving technique - but still with room for improvement.

Re: suspension - where are you now and what are you going to? Steady-state cornering your car will oversteer? Doesn't sound helpful...

Yes, much room for improvement . . . thank God.

My car has been described as maneagably evil. It feels like it is very heavy in the front such that the tail can get happy at any moment. Yet, if you push the car hard, it will understeer. It is a lot of work to drive fast. My solution is to drive extremely smoothly and stay on the gas no matter what. If I need to address understeer, I do throttle blips as necessary, but I don't like to modulate the throttle for fear of the rear . . .

I am getting an new suspension next month. The guy swears it will be night and day from what I am experiencing right now . . .

[924RACR]

Ick. And you were all over rennlist worrying that you were just a bad driver???

You running blown-out shocks or something?

[TD in DC]

Originally posted by 924RACR
Ick. And you were all over rennlist worrying that you were just a bad driver???

You running blown-out shocks or something?

well, I'm not a great driver. I can't wait to see what my times will be like with a real suspension. Right now, I am about 3-5 seconds off the podium guys of my series. There is a chance I will be right there once my car is sorted. It is also overweight. Well, let me rephrase, I am probably a little overweight and so is my car. I should be down to class weight very soon . .

There are a number of reasons why my suspension is not "right." I am going to make a comprehensive upgrade and do it all at once. It will be $$$$$$ but better to do it once and get a known complete "system" from a local guy who will support.

The guy says that I should be able to drink a coffee while going around the track in the 944. Good thing . . . maybe it will make the 944 feel more like my 996, but it still lacks the in dash espresso machine.