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Critique my VIR vid please (be gentle)

 
Old 03-25-2008, 12:29 PM
  #61  
TD in DC
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I have no idea whether the original poster is still watching this thread, or whether he appreciates people taking the time to respond to his request for critique. However, I have been receiving e-mails asking for a little more information about some of the issues I raised, including about coasting and maintenance throttle.

The best way I can think to show this is by showing the data comparing my driving before receiving instruction from Chris Cervelli, Chris Cervelli driving my car, and then me driving my Car after being instructed by Cervelli. Unfortunately, I have this data from Summit Point rather than VIR. Nonetheless, the theories are the same, and I think that looking at T1 can illustrate some of what I have been talking about, including the line.

In the charts I am posting here, the black lines always represent me driving before Cervelli, the red lines represent Cervelli driving, and the green lines represent me driving after being in the car with Cervelli while he drove. All of this is in a normally aspirated 1984 944 with a whopping hp of 147 at the crank. Although you naturally would have to be much more judicious with getting back on the throttle with a 400 plus hp at the wheels 996 Turbo, the ideas remain exactly the same.

The first chart shows the lines. Think of it as an aerial view of T1. As you can see, Cervelli did a much better job of making the radius of the first part of the turn (pre-apex) as large as possible. You can see how he turned in sooner and went out farther. The radius of the second half of the turn is smaller. As I explained earlier, this is because we don't need the radius as much in the second half due to the lack of acceleration, but we can use the radius in the beginning to carry in as much speed as possible. If you were in a high HP car, I can imagine that you would do the opposite to some degree, and you might take one of the lines represented by the grey plots (although not the one where I slid off the track ).

The next chart shows the speed through the turn. As you can see, the exit speed never really changed, which means that we both were getting the max exit speed possible for my car, so the next step was to focus on entry speed and carrying as much speed as possible through the turn. As you can see, before I saw Cervelli, I braked a little too much. The hard V shape of the black line shows that I was hard on the brakes and then hard on the gas. As you can see in the red line, Cervelli braked sooner but more gently, and then trailbraked the car through the corner, carrying much more speed than I had. Again, the exit speeds were the same, but he was faster due to losing less speed going into and through the corner. The trailbraking resulted in a "soft V" shape, but he was either on the brakes or on the gas the whole time, he just had to transition between the two much more gently than I had in the black lap. The green line shows that I did a fair job of imitating Cervelli.

These should be similar for a high HP car, except that mph should start out much higher, the braking zone would be longer, and the acceleration zone would be longer, albeit likely at the same slope for both braking and acceleration until you hit the next corner. Now, since the car is more powerful, you could get that same acceleration slope with less throttle, but again, you would still use the throttle to accelerate (rather than coasting or maintenance throttle).

The next chart shows longitudinal Gs, or braking and acceleration. Going into the turn, I am at max speed for my car (don't laugh), and it shows that I am only able to pull 0.1 Gs. of acceleration at the upper end. You can see the braking, and how Cervelli (in the red line), was constantly on the brakes through the turn, albeit at less pressure than I used. Again, really no maintenance throttle or coasting. Rather, on the brakes or on the gas, but not full brakes. The green lap shows that I was not as smooth at trailbraking and braked a bit more torwards the end to get a little more rotation. I didn't lose speed, but I need to emulate Cervelli's braking a little more. Then you can see that we were on full throttle to stop rotation and exit the turn. With a high HP car, you would have to be more judicious, but the principle is exactly the same. As you can see, at a lower speed, I am able to pull a whopping 0.2 Gs. of acceleration.

The final chart shows lateral Gs, which shows how most of the work was done well into the turn. I would expect that, while the shape would be similar, the graph for a properly driven high HP car would be shifted to the left a little.

Again, there are always exceptions, but this is just a good example with data to back it up. You may think I am a ****ty driver (and you might be right), but I assure you that Cervelli is awesome and knows what he is doing.

Hope some of you out there find this interesting and helpful.

For those of you who think it is spaghetti,
Attached Images     

Last edited by TD in DC; 03-25-2008 at 12:48 PM. Reason: Oops, I fixed the misordering of the charts. Sorry.
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Old 03-25-2008, 03:15 PM
  #62  
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Great post TD. I still occasionally go back to the original dorki thread on this to read.
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Old 03-25-2008, 03:24 PM
  #63  
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Originally Posted by ZAPmobile View Post
I am much more impressed with someone doing a 2:10 in a 250hp car that meets all the PCA specs of a stock class racer.
That would be something....even if the camber plates weren't centered.
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Old 03-25-2008, 03:45 PM
  #64  
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Originally Posted by ZAPmobile View Post
I am much more impressed with someone doing a 2:10 in a 250hp car that meets all the PCA specs of a stock class racer.
Originally Posted by forklift View Post
That would be something....even if the camber plates weren't centered.
x3
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Old 03-25-2008, 03:57 PM
  #65  
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Originally Posted by forklift View Post
That would be something....even if the camber plates weren't centered.
Wasn't it your video of the RSA turning 2:10 and change?
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Old 03-25-2008, 04:05 PM
  #66  
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Originally Posted by forklift View Post
That would be something....even if the camber plates weren't centered.
Dude congrads again!!!!! that was awsome time you ran at the track i was very impressed... kinda what Arnie was talking about... 262 hp car and that kind of time!

matt
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Old 03-25-2008, 04:12 PM
  #67  
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Originally Posted by ZAPmobile View Post
Wasn't it your video of the RSA turning 2:10 and change?
Yes, thanks. I just can't get past the whole camber plate thing as I prep my car for G class. Still need a cage, cutoff, suit etc. so a while to go before I figure it out. If I have to run -1.5 camber and crush the outside of my tires, then I guess that is what I'll do. Car has stock (un-rebuilt) 95k motor, stock chip, stock gearing and stock calipers.

I don't think we've met. I'll look you up at the next VIR event, which for me will be Potomac in Sept.

Jim
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Old 03-25-2008, 04:14 PM
  #68  
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Originally Posted by 930man View Post
Dude congrads again!!!!! that was awsome time you ran at the track i was very impressed... kinda what Arnie was talking about... 262 hp car and that kind of time!

matt
Thanks Matt! Congrats on your 2 flat. Nuts.

Not sure what hp I have. Just have the cat and primary by-pass....262 fw is probably close.
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Old 03-25-2008, 04:18 PM
  #69  
TD in DC
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Originally Posted by forklift View Post
Great post TD. I still occasionally go back to the original dorki thread on this to read.
Thanks Jim!

Now, unlike me, Jim really is a fast driver. If he can turn a 2:10 with 260 HP, imagine what he could do in a GT3, TT or GT2, even if they were stock.

Although I am haven't caught up with you, Jim, yet , I think you understand my thinking . . .

I was only able to hit 2:24s on RA1s. Of course, that is with 147 hp at the crank. My acceleration is pathetic, and I can only hit 105 max speed (indicated by data, 110 indicated by speedo). Other 44 Cup drivers with hoosiers can take seconds off of that, so I still have my own learning to do.

Of course, it is very possible that I will not do any more DEs. To the extent I get back to the track, it will probably be for racing.
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Old 03-25-2008, 04:21 PM
  #70  
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Originally Posted by forklift View Post
Yes, thanks. I just can't get past the whole camber plate thing as I prep my car for G class. Still need a cage, cutoff, suit etc. so a while to go before I figure it out. If I have to run -1.5 camber and crush the outside of my tires, then I guess that is what I'll do. Car has stock (un-rebuilt) 95k motor, stock chip, stock gearing and stock calipers.

I don't think we've met. I'll look you up at the next VIR event, which for me will be Potomac in Sept.

Jim
Look forward to it , just look for the Zapmobile. I run in red and Margo runs in black
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Old 03-25-2008, 04:40 PM
  #71  
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Originally Posted by TD in DC View Post
Thanks Jim!

Now, unlike me, Jim really is a fast driver. If he can turn a 2:10 with 260 HP, imagine what he could do in a GT3, TT or GT2, even if they were stock.

Although I am haven't caught up with you, Jim, yet , I think you understand my thinking . . .

I was only able to hit 2:24s on RA1s. Of course, that is with 147 hp at the crank. My acceleration is pathetic, and I can only hit 105 max speed (indicated by data, 110 indicated by speedo). Other 44 Cup drivers with hoosiers can take seconds off of that, so I still have my own learning to do.

Of course, it is very possible that I will not do any more DEs. To the extent I get back to the track, it will probably be for racing.
Thanks TD, but I still have lots of work to do. I think a high :08 is in that car as is...but it will take a while, which is the fun. Wish I could get down to VIR more more than a few times a year to work on it, it is my favorite track.

Besides you kicked my *** in karts.....and I still need a rematch!
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Old 03-25-2008, 05:17 PM
  #72  
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Jim, your lap looks great. I can't find any time for you on it, so sorry. I think getting out of Oak Tree any faster ain't gonna happen. You may get into Oak Tree a little faster, but your exit is really good. Using your bar as a goal on Friday at Test/tune before the race on practice tires (MPSC's). PS. would not mind looking at your run file if you don't mind. BTW, you can run PCA for 4 races with a bar, just do it now and get out there.
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Old 03-25-2008, 05:40 PM
  #73  
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Originally Posted by forklift View Post
Besides you kicked my *** in karts.....and I still need a rematch!
Don't think I am going to forget that for awhile. Considering how much I weigh versus how much you, Mark and Sam weigh, I was pretty proud of that accomplishment, even if the flaggers were showing me signs telling me to stop using the gas and the brakes at the same time.
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Old 03-25-2008, 05:50 PM
  #74  
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Originally Posted by TD in DC View Post
Don't think I am going to forget that for awhile. Considering how much I weigh versus how much you, Mark and Sam weigh, I was pretty proud of that accomplishment, even if the flaggers were showing me signs telling me to stop using the gas and the brakes at the same time.

Yah, but I heard that the tires on their karts were pretty worn...........
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Old 03-25-2008, 06:20 PM
  #75  
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TD, at least you didn't get black flagged like I did. Oops. We should go to Alsports in the next few weeks like we have been talking about.

Bob, thanks but I still am leaving time on the table throughout Oak Tree. I need to brake later and trail the whole way through I think. Toby in his Boxster has a minimum speed of around 50 on RA-1s and mine min is around 43-44 on Hohos. I think I have time in Southbend, T1, and T3 also....probably others, but those especially.

Good luck at VIR this weekend!
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