Bill Dearborn was kind enough to share a PDR file of his PB 2:04 lap of VIR Full and I wanted to compare that against my current PB of a 1:59. Bill is on Pirelli slicks and I'm on Michelin Cup 2 tires but the lateral G's are nearly identical with both of us pulling just over 1.5G in places. For starters, here is a screen shot of the entire lap in Cosworth Pi toolbox and this includes the video which isn't available in the free version. For data, all I'm looking at for now is accelerator (0-100%), brake (it's percent of pedal travel which can be deceiving), Speed, and time delta.




So let's break this down a bit. Up until the apex of T1 you can see that Bill and I are pretty much even despite the fact that I'm running a good 4 MPH prior to braking zone. We both brake at the same and I start with more brake effort and trail it off as the speed drops. This is to take advantage of the additional grip you have at higher speeds from the downforce. Bill and I both reach about the same apex speed and you can see that we're still neck and neck.




Leaving T1 you can see that I can to full throttle much sooner than Bill and the result is that at one point I am 8 MPH faster in the run from T1 exit to T3. Some of this is undoubtedly the DSC Sport controller because it really helps this car put the power down.

You can't see it on this chart but I also took a more shallow all the way through T3 and went all the way over the curbs getting back to the power sooner. Bill took a wider arc through 3 but didn't use the extra pavement on exit. This all resulted in about a 0.8s improvement in time.




However, coming out of T3 I brake much earlier than Bill and for that section of about 1000 ft he has up to a 20 MPH speed difference on me. The result is that I give back over half of what I gained in the previous section and the gap is back ~0.4s.

Again I take advantage of little straights to go back to WOT and build speed. In this case it's the short straight between 4 and 5a and through that section in places I have a 13 MPH higher speed. Bill does carry the throttle more through that section but by the time we've both turned in to 5b and starting the lower esses I have a 6 MPH lead and am back to being ~0.8s quicker.




The run up to the climbing esses is pretty self-explanatory. The faster speed coming in to the lower esses, getting back to WOT sooner, and keeping the throttle pinned nets about a 10 MPH speed difference in the run up to the bridge. Bill starts breathing off the throttle almost as soon as he exist the lower esses and lifts fully just before crossing under the bridge. By this point the difference is over 2 seconds. Staying in the gas longer nets me another 0.2s but to be honest I should have stayed in the gas much longer myself. Bill also brakes and enters the climbing esses at 122 MPH where I'm at 142 MPH.




Comparing the way we handle the climbing esses is fascinating to me and shows that I can learn a lot from Bill. You can see that I am barely on the throttle except for brief stabs as the car is straight. Bill maintains a near constant throttle and the result is that by the time we are making the final right-hander our speeds our equal. Bill also continues to accelerate hard between 9 and 10 where I am pretty much coasting. The result is that there very little time difference at the top of the esses when we enter T10 and by the time we exit T10 it's ~2.8s difference.




More to follow…

 

Now let's look at T10-T12 (oak tree). The run down the hill from T10 to T11 is pretty even but this image from the GM Cosworth toolbox clearly shows the different lines we take. I took more of a wide arch through 11/12 whereas Bill took a more traditional line of squaring off the corner. I picked this up watching IMSA races on TV




The result is that my min speed through T12 is about 8 MPH faster but Bill gets back to full throttle sooner. This does get me about a 0.5s increase in lap time but the speed differential is pretty much erased by the time we pass the exit curbing of T12 and we are again neck and neck down the back straight.




When we reach the end of the back straight I've somehow managed a 4 MPH speed differential when Bill lifts and I stay in it about another 500 ft getting me to 157 MPH indicated VMAX (probably more like 162 MPH based on what we saw comparing GPS to indicated speed). That extra speed carried until the apex of 14 at the end of the back straight gains another 0.7s.

I also carry the speed a little longer to brake over the gaters at the top of hog pen. This little section is good for another 0.3. Finally, exiting hog pen I am back to WOT a little before Bill and that gives me a 3 MPH advantage down the front straight that is good for the last couple of tenths.



I hope this has been helpful for folks and again I want to thank Bill for sharing his data and letting me do this. Overall our lines were very similar except T3/4 where Bill was clearly faster and T11/12 where I gained in lap time but with no real effect on speed down the back straight. I hope this also demonstrates that even a 5 second delta takes doing a large number of things differently and there is no magic. I laugh at generalities like "slicks are worth 2 seconds a lap" because you still have to adapt how fast you turn in, the speed you carry, and when you get back to WOT to take advantage of any performance improvement.

In making this I ended up also using the GM Cosworth toolbox because it does some things that Pi doesn't do. The first is that it is great for seeing your actual line overtop of overhead imagery. The other is that when comparing laps things can sometimes get slightly off because you can't compare on time and distance will get skewed by different lines or even tire sizes. In particular, the video window in Pi was totally out of sync with the chart by the time we got to T10 As a result I used the charts and video in the GM toolbox to reference what I was seeing in Pi and make sure it was correct.

 

While I didn't use this for the lap comparison I wanted to show off a little bit of the eye candy that comes with Pi toolbox and a 2018 (or late 2017 in my case) C7 PDR. First is a look at the suspension travel that is now recorded and using a math channel you can also graph suspension velocity.





You can also graph engine performance parameters like engine torque, boost, IATs, and ambient temp. In particular I've found comparing torque useful to see how much power you are actually losing due to high ambient temps or heat soak.

 

Watching...hopefully learning.

 

WOW!!!!

Very interesting!!!

 

There is a greater speed difference than what appears in the data. The Pirelli 325/660/18 slicks are smaller in diameter than the Cup2s that Sean is using. The Cup2s have an overall diameter of 26.6 inches Vs the Pirelli's at 25.98 inches or ~ 26 inches. 100 mph indicated on the Cup2s tires is 102 indicated on the Pirelli's.

Bill

 

Interesting point Bill. That prompted me to go look at some Aim Solo data since it has GPS as well as indicated speed. Interestingly enough the data shows that both tires track closely to one another and in both cases the delta between indicated and GPS speed is pretty minimal until about 120 MPH.

After 120 or so the delta starts growing until VMAX on both tires. I wonder if that is from the tire growing in diameter at high speed? Pretty interesting and here is the chart. The orange lines are GPS and indicated speed on 325/660-18 Pirelli slicks. The green lines are for the MPSC2 tires.

 

keep it coming guys .

 

Updated 2nd and 3rd posts with the rest of the lap and some extras.

 

I have used both lines but didn't realize the other essentially early apex of T12 provided that much benefit. I have been also using a line where I come in wide like Sean but then stay wide into the entrance to T12 and make my normal turn in. I am scheduled to do a one day event at VIR a week from today so I will try that line. Maybe shoot to use more of the inside and outside curbing to widen the radius and carry more speed through the corner. I am comfortable with that turn so hopefully making a change won't be all that hard.

Bill

 

Sean--Back to post 1....did you spring for the full version of PI? Or is everything you did available in the free version except for the video? Also did you and bill have the same ".map.gpx" file...thus the same start/finish line?and if not how did pi handle the analysis without the common starting point?

Thanks

Bill

 

We did not share gpx files.

Bill

 

Everything you saw except the video can be done with the lite version.

 

Do you need a 2018 PDR to be able to use Pi Toolbox? Or is there a way to extract the data from the video/export the data from the GM Toolbox software? I only see .mp4s and a .gpx file on my data card

 

Sean used the mp4 file from my 2015 PDR to make the comparison between my run and his. It will work with the older files. You just have to figure out how to get it to work as the user guide leaves a little to be desired.

Bill

 

Thanks Bill! I dug a little into the more detailed instructions and (mostly) figured it out.

 

Guys, this is better than ****; thank you for taking the time to do this analysis!

I've been spending a lot of time comparing outings & what you can learn from the data really compliments the seat time.

 

Thanks. I'm trying to figure out if this would be worth trying to do live at an HPDE classroom session.

 

I was thinking more about showing folks live data and how to walk through it.

 

I'm pretty sure Youtube has plenty of examples of how to screw up the climbing esses .