How do you learn to crash?
 

Thought that might get a few views and opinions. I've started the thread with quite a lot of content but thought we may as well get as many facts out from the beginning.

Ok so I got myself into a situation 10 days ago at the track. First time I had the car back out there since late 2010 after a large number of changes. Apart from a bit of 'Ring Rust' (Boxing term, not in relation to my leakdown numbers) I was finding the car a bit jittery. The tail had stepped out previously that day and we removed the rear sway bar completely for a temporary fix. The builder is of the opinion that the rear springs are too stiff (just over 900 front and 1100 rears) however this is a kit that I bought from Moton for a race prepared 944 turbo.

As you will see in the video I am going through a long left hand constant radius corner. I was travelling about 145mph before light braking. You can see that I make an initial correction but then soon afterwards the tail just steps out on me. There has been much conjecture and supposition as to the cause. Some think the car in front was probably spilling some fluid based on how much unburned fuel was pouring out and how I described the car as a bit of a shade tree 'Special'. AlfaSud with a mid mounted Rotary 13b motor and what looked like a GT35 turbo. Meant to be good for about 600hp but not so much on this particular day as I saw him working pretty feverously on it in the pits.

People have also said I over corrected and caused my own demise. Well this may be true to an extent however they weren't in the car and didn't experience the total sudden full loss of traction. Couple with the one pressing thought in my mind which was to avoid snapping back across the track and into the Left hand inside wall at all costs. We've seen too many cars do this and end up in bad accidents and rollovers. So I was determined not to let this happen.

After this however was where I was lost at sea. The grass was totally sodden due to a week of record breaking torrential rain so there was no slowing down over this. Then into the Gravel which didn't seem to slow my progress much either. Finally spinning about 90o to hit the wall pretty much perfectly side on which may have been the best thing for the car. Not so much for me as you'll no doubt agree.
Broken ribs and nasty whiplash but overall very lucky to be up and about straight away. Adrenalin is amazing stuff.

So anyway, apart from a burning desire to figure out the cause (more on this later) I realise that I just didn't have any moves in my armory to pull off once I left the track. Should I have tried to spin the car at some stage either through handbrake (not easy to access in a 951) or a sharp tug on the steering wheel?
Should I have tried to rotate the car or would this have seriously increased the chances of a rollover? These are the things that I just don't know and wonder why we don't get any form of education in matters like this?? Perhaps nobody will give us this advice in such litigious times but there must be some info out there to enable a fighting chance of avoiding massive impact?

GO952 crash April 2012.wmv - YouTube
Note the car in front do a pretty obvious tail wag on the last corner before main straight on final lap....(as I'm continuing to stumble ineffectively groping for my new 3rd gear! Hey it's a new 6 speed trans and I said I was rusty! )

So according the the engineer he is of the belief that the rear suspension doesn't have enough droop and is causing the inside rear wheel to actually lift which of course reduces traction by approx 25% but also creates that imbalanced Jacking motion. It seems very unlikely that a car such as this would lift a wheel on such a corner but the data points to this. So once we pull the car down and check we will know what was the cause...or I'm not going out in it again! The other possibility was that we were running pretty high boost levels (23psi) and there may have been a bit of headlift which could have caused coolant to drip down onto the rear wheels. I don't think this is the case but have had this happen in the past and I went off without warning in similar fashion although much slower on a different track. Also didn't notice leaks in the pits that day. I haven't been back to the car yet for a few reasons. Hope to see it this weekend and perhaps find something apparent.

Here are some thoughts from the Engineer:

Hi Patrick
I’ve been analysing some of the data in more detail and what I have discovered is the following.
We have been using 45mm of rear damper travel at the track. This probably equates to around 70mm of wheel travel.
Unfortunately the car needs to have more droop travel through some of the higher G force turns. The inside rear wheel is lifting off the ground, this is the jacking effect that Paul was talking about, at the time we thought it was being caused by too much rebound damping and we removed some.
Factory setup have the droop controlled by the bolts retaining the outer torsion bar bush, your application probably has the rear droop controlled by a spacer above the piston within the damper so some damper or rear suspension setup mods will be required before the next outing.
If you look at the data particularly suspension position [position each corner in a new graph on the page] you will see that the lr suspension pots flat lines during some corners at around -22.
At this time the rear wheel is starting to lift of the ground and the rear will start to become unstable.
Your video also confirms this as you have to correct your line on entry , you were travelling 16 klms quicker than the previous lap and the gpsmap shows you wider on entry before the apex which all added to the event.
The rear end appears to be rolling more that the front but a more accurate measurement of motion ratios would be required before you could call this a fact.
Everywhere that the lr suspension starts to bounce off the full droop point is where you were complaining about a lack of rear grip so we need to rectify this before next outing.
If there are no spacers within the damper then we may need to get extended rose joints, Im a bit surprised that this has occured given that you bought the dampers to suit this application.
Mark
Rsport Race Engineering

When I put the concept of disbelief to the engineer that we were getting inside wheel lift on this corner he replied with the below paragraph. Unfortunately I can't upload .pdfs so I have put in a link to a thread on Rennlist for those that want to see the screen capture data from the shock pots.

See post #578 Patrick's build thread. (IT RUNS!) - Page 39 - Rennlist Discussion Forums


Hi Patrick
Please see attached screen capture. Unless the rear wheel managed to hold at exactly the same height for over a second on each of the three occasions as you turned in I would believe my comments to be correct. I think the wheel lifted on entry and you were a victim of the grip slide shimmy scenario on entry to the corner which caused your mid corner correction and subsequent running wide on exit. I'm not saying that the rear shock has definitely bottomed out but something has definitely stopped suspension droop at that point, the most likely scenario is that the shock has runout of travel but regardless the situation needs to be reviewed to see what has caused the suspension to stop its travel and cause wheel lifting at that point.
Please note if you look at the capture you can see a similar trait in the right rear shock as you leave the track at about the same level of droop.
The 'grip-slide shimmy' is when the rear end grips and then slides and requires steering correction to maintain line through the corner.

Also to note the car was running on 10.5" x 18" 285/645 front and 11.5" x 18" 305s rear. Brand new Hoosier R80 slicks. Also while we had a pretty decent front splitter on we haven't had time to put on the large rear wing so have only had what is known as a Hoop spoiler from the Factory. This could also have affected the balance front to rear.

That was a bad hit, Patrick.
Great to see you came out ok.
As to the cause, unless I was driving at the time I cant help.
Keep your chin up.
I once destryed a 40k engine before it was even in my car.
I know how you feel.
Good luck finding the cause. :(

Sorry to hear about the crash -- and relieved that you seem to have avoided serious injury.

Very tough to have that happen just when the car has come back from a long build.

If the problem were as simple as the architecture of your suspension, then wouldn't you have noticed the intermittent loss of grip in the earlier trips through the corner? I'm the furthest thing from an expert, but I wonder if your toe setting came out of adjustment (I've got no idea about how it's set on your car). I say that based on my own experience, where an eccentric bolt was just loose enough to drift out of its setting in the course of a session, leading to a similar high-speed off.

You may never learn what went wrong. But when the car comes back, I'd do some more rigorous testing of the handling before I'd go out on a track like that one. The stakes are pretty high with corners that fast. (That track looks like it would be a lot of fun to drive, by the way.)

You're also due for a Hans or Isaac or similar head and neck restraint. The distance your head appears to travel is kind of scary when you consider how little is needed to induce a basilar skull fracture.

Glad you're okay.

Patrick- tough week for 951's! We both just spent a boat load of money (you more than me, admittedly) and I also wrecked my car last Sunday! $7k in front end damage- a Lotus spun in front of me and I had no where to go. Anyhoo, be thankful your drivetrain is OK and you are not on a breathing machine.

+1 with Jack. Get a HANS or something. You're in a race car now.

The rest of the stuff makes perfect sense. Not enough rear travel, possibly a stiff rebound set-up and it seems the Motons may have been spec'd out taking that big ass rear wing into account. I don't think you'd have any rear lift with that thing hanging out the back.

Could be fluids on track, but your datalogger strongly indicates it was the set-up.

I know from experience, once the 951 starts rotating, it moves really quick. Not sure our hands are fast enough to counteract.

Sometimes there's just mistakes too
glad your ok.. but get a HANS or equiv. so you can crash again another day :)

Yes the safety aspect will be increased with Hans, Halo, and Net next time. I agree, I was lucky although at times it's a little hard to feel convinced of this. Oh and it was my birthday haha.

The thing that I can't seem to get any information on is should I have rotated the car once off the track or is that just too much an unknown factor?
What would you guys have done once you were heading to the outfield?

There were some signs of suspension malcontent previously and we did adjust the rear rebound plus remove the rear sway. That turn also has some bumps through it and can be a little unsettling. By muffing the 3rd gear change on the turns leading onto the straight I had left a bit more of a gap between the car in front which allowed me to come into that turn 16kmh / 10mph faster than the previous lap, but I have been through that corner plenty of times at what I guess is close enough to that speed.

Gorilla, sorry to hear of your crash. Hope you get it back soon. Assuming you're OK?

nb Jack, that is the short North track that they've recently opened. There will be another South track so they can run 2 events simultaneously. Here's the old GP track in my car back in 2010.
Eastern Creek PCNSW 5th Supersprint 17.10.10.wmv - YouTube

The fact that you had the nerve to down shift while you are about to hit the wall was pretty amazing; I would have just closed my eyes at that point and held on tight.

I watch a lot of Formula 1 and even with the best drivers in the world, when the bad stuff happens, sometimes you are just a passenger. All of the new F1 tracks have asphalt runoffs, for this very reason. Hit grass and gravel and there is virtually no car control or controlled slow down.

I beat myself up a bit too last weekend, trying to figure out how I could have avoided my collision. Without going off course and possibly losing control myself, I had nowhere to go- the guy was stadling the track and rolled right back into me.

I even looked through my racing books to see what pro drivers try to do- yeah, nothing there.

Sometimes you just do not have enough time to make the right decision. Reviewing you video, from the time from your fatal twitch to the time you went off course took less than a second, then less than 3 seconds to hit the wall. Not a lot of time. I'd be suprised if the best drivers in the world would have been able to recover that one, even given a few chances.

With the weight of our cars at opposing ends of the chassis, when we lose traction, the car is going to want to CONTINUE to spin more than other cars and with equal wieght at either end, how do you know which direction the car will spin next?

I just don't think there is a good equation for that

Yes, others have remarked on the downshift. Not sure if it scrubbed off any speed but it was all I could think of at the time. I’m sure there was an element of ‘Deer caught in the headlights’ syndrome too in which you become slightly paralysed and just a passenger…but damn I would have liked to have done something more.
Is there just a basic adage of keeping the car straight when off the track so as to avoid any chance of a rollover? Wish I knew more.

I think it would be better to not be going sideways to avoid a roll, but generally, I think if you could control that you wouldn't have been crashing in the first place. I just dont see any driver in the world saving that once the car was off the pavement. Grass isn't know for grip. I've seen pros in similar crashes, they don't even try to save it, they take their hands off the wheel and hang on to their belts, or cover their head and prepare their bodies the best they can for the impact.

Sorry to see this happen to you, but glad you came out if it without too many injuries! The only thing I would add has been touched on briefly. Letting go of the wheel before impact.

Hope all goes well with your comeback.

M

Ouch.... I personally think something in the suspension came loose or failed. Maybe something was not torqued right.

"Two feet in"

and thumbs off the wheel...

At some point you are just along for the ride

Check out what Danica does just before she hits the wall... hands off the wheel

<div><iframe frameborder="0" width="576" height="324" src="http://d.yimg.com/nl/yahoo sports/site/player.html#vid=28407836&browseCarouselUI=hide"></iframe></div>

Also did you notice the water that sprayed onto her windshield?

I hit some tire barriers once, and got drenched with swampy, stagnant, mosquito larvae infest swamp water that must have been in the tires at Summit Point for years..

It was effing disgusting...

that's reason enough not to hit one. I think Danika's water was from her radiator though.

Any pics of the damage? How bad is it?

Sears Point has some nasty, brackish water.

http://forums.pelicanparts.com/uploa...1134533445.jpg

Here's the foolhardy driver, moments before impact.

http://forums.pelicanparts.com/uploa...1134533340.jpg

Closer in, you can see that it's a calm look, considering that I'd driven the car 364 miles to that track and would soon have to figure out how to drive it back home.

http://forums.pelicanparts.com/uploa...1134533351.jpg

I'm looking in the direction the car is heading, but you can see the gasses expanding under the tires faster than it's moving, so the smoke is actually leading the way.

For the record, I did not bring my arms in, Danica-style. I haven't crashed enough times to have burned that into the circuits of my brain stem.

I keep thinking that I should have held onto my helmet and braced myself. I remember ducking down but that was after the impact. Situations like this can be quite surreal. It's as if you're in your own movie.

I haven't been back to the car since the crash. We took it back to the workshop and put it on a hoist and it's sat there ever since. We had a bit of a look around from underneath on the night and it 'seemed' ok but no real checks have been done.
I'm going back there this weekend to have more of a look and hopefully the following week it will have the damaged panels removed and we can assess the damage to the chassis etc. The Windscreen/roof appeared straight and the chassis rails from underneath looked straight. The left hand tie rod is bent but the rest 'appeared' ok. I think I was very lucky to have hit pretty much perfectly side on and into the tyre barrier. They absorbed a lot of the impact and sort of wrapped around the left hand side to a degree. Fingers crossed all I will need is some more panels and a bit of paint...but I've learned to harness hope in this field.

First, I am sorry that you hurt your car and that you were hurt. I hope that you mend fully without too much discomfort and hassle. And that your car gets fixed without too much cost and hassle.

Now some observations in no particular order...

1.I don't know how much experience you have with those tires. Scrubbing back and forth like that as you head on the track does little in my experience, unless you have a bunch of easy-to-get-off crud on the tires. When I move back and forth on an out lap, it is for nearly the entire lap, and I do some things like drive really side ways in certain corners to help further build some temp and get rid of the crud. This is my experience with slicks. I did not see anything in the video that suggested you did much to get heat into the tires. Just an observation.

2. The camera seems well placed, but I think it would be helpful if you had a brake light indication somewhere in the FOV. Even with data acq, I am a believer that a brake light in the FOV is helpful. I have both a brake light and a WOT light in my car in the camera FOV.

3. It never looks like you are working the tires in the video. I see no real corrections like you are getting anywhere near their limits and using their grip. I am not sure why it appears that way, but generally it looks to me like you were not "up on the tires" at all.

I might expect this in the early laps with a new car build after not having driven for a while. That would be good judgment building up confidence in the car and learning its behavior in an effort to learn its pluses and minuses.

Given a cautious step-by-step approach in terms of cornering speed in general, some would also take late apexes-- that is later than the proper apexes for the corners. I do not know whether you were doing this or not. I think going late as you are building experience with a new car is important, especially with a turbocharged car. No matter what gauges and data tell you, you have to get a feel for boost. It is different in different gears. Ask me how I know... (3rd gear boost oversteer in a slow corner at Laguna Seca).

4. More on the car... I do not remember what type of seat you have, but I can see a lot of your back/shoulder, and that is unsettling. And as mentioned, a head and neck restraint is likely prudent.

5. To me, it looks like you are taking a too early apex, with cold tires and in a situation where you could get a somewhat sudden infusion of power from boost curve climbing. The rear tires seem to say, "No thank you... I cannot accelerate and corner based on these input data. My performance limits are exceeded and I will now give up all grip."

Sure, it could all be a handling/suspension deal, but I personally doubt that unless your car is vastly different from other 951s with which I have had experience. You have to make sure you have enough suspension travel and all of that... don't want to see a sudden infinite spring rate. But I'd expect other corners to reveal that...

That corner may be just a little like turn 1 at Thunderhill, but it is hard to say. I have only seen a few folks go too early at turn 1, but i did see a 993 GT2 factory turbo car suffer from not losing enough speed on entry and he wound up in the turn 2 worker box tires. His rear tires let go first with a "what, are you kidding? No way, see ya grip." One of our local guys was driving.

6. I am not sure what you could have done differently in terms of deciding what to do after the tires let go. I see a bunch of entry corrections and maybe there was a lift... but it is difficult to get a good recovery when you are going that fast... especially if the tires are cold and the car is somewhat unfamiliar and the driver is rusty. Obviously wet grass is no help.

One of my former students recently went early at a corner at Thunderhill... wet grass and soft ground caused lots of damage that wouldn't happen in the summer. He was in a new build and still learning slicks and I figure he went early, and maybe the tires weren't yet up. This was in a 911, which is much easier to drive than a 951.

Again, sorry about the accident, and hopefully you will be able to get back up and running quite quickly.

I remember that sequence of pics from the past Jack. Sorry to say but they are quite memorable and I love that close up. So much going on.

Mike,

Thanks for taking the time to respond in detail. I guess I'll address each numeric point.

1) Don't know the tyres that well. Have only limited experience driving them and slicks on the whole. In general haven't had issues in the past when on them though. There does seem to be some conjecture over them in some circles...the Hoos I mean.
Have never had to scrub a huge amount in my car (mostly on RSpecs) and my friend who drives a similar cars on similar slicks doesn't scrub in at all...but it's not to say that you don't have a very solid point.

2)Assuming you mean to have brake and wot lights visible on film for analysis later? I will have a better setup with data overlay soon enough. Or do you mean as reference while driving?

3)No, basically you're pretty correct in that assumption. Although the track layout as shown is either pretty fast or very slow corners. Not much inbetween. T3 is probably the one where I could have loaded up the tyres more. (T1 being the crash turn for reference). What you see is me pretty much pootling around the track trying to get a feel for the new car. Having said this, the track is actually more a momentum track that you need to string corners together. Well the full track is in any case.

4)It's an OMP seat similar to a Recaro or Sparco. I have my eye on either a new Cobra or RaceTech seat and will have Hans and net as well.

5)Again, probably right. Although funnily enough I would have liked to have taken an earlier apex at T1 as there is a bit of a groove through there, but yes, I have to agree that some of the turn in points were too early. I have a bit of a gut feeling that if you are really on song, an early apex in some cases is the fastest way around some corners...but I wasn't on song or particularly confident with the car being a bit twitchy in general. The tail had stepped out previously and it had picked up a wheel at T2 which we thought might have been the LSD at one stage.
The car is at the upper end of most 951 builds but not sorted. There is still a large rear wing to go on and I'd like to do some underbody aero work.

You can read about the build on this thread. Please ignore the rubbish that killed it off! http://forums.pelicanparts.com/suppo...eys/behead.gif

http://forums.pelicanparts.com/porsche-autocross-track-racing/661835-my-build-what-its-worth.html

6)I'm getting the general impression that I was pretty much toast once off the track. Even though there is video of the whole thing, in my mind it still appears like a slow motion 'click-click-click' photo sequence and so I don't realise how much speed I was carrying when thinking about possible alternative strategies.

Interested to hear your take on the 911 vs 951 theory? The 944/51 is an easy car to drive pretty quickly but I think to really push it you start to slim down the window of forgiveness. Whereas the 911 is a known quantity and most will probably follow the 'slow in fast out' theory and do pretty well with that. The way they get out of slow to medium corners is unparalleled but the 951 is faster through high speed sweepers and I find under brakes too.

+1 on the Racetech. That's what I just put in. It's a bit odd, as the seat really hugs you right up to the armpits and with the halo, it's a bit tough to look around hairpins, but one thing is for sure....

I ain't goin' anywhere.

Patrick, why are you giving Winder a lead-in like that! The 951 is well balanced and is a very stable platform. However, at certain unfortunate trajectories, our cars have more in common with a spinning top!

Of course as you know, it is hard to tell anything from a video.... but here are some additional thoughts...

1. As you likely know, all tires have an optimal temperature, pressure and slip angle for max grip. The former two are in a range.

I have about 25 years of track driving experience, 10 of those on DOT sticky tires and 10 on full slicks. What I have learned from expert friends and my own experience are some techniques for getting the slicks up toward temp and pressure range. These techniques are different from what I did with DOTS. I think the DOTS get where they need to be faster from normal driving than do full slicks. On slicks, one of the benefits of the process is that I get some feedback as to where I am in the process before I start pushing.

2. What I mean is to have some type of light in the dashboard that is setup to come on with the brake lights. It doesn't have to be huge, just big and bright enough so that you can see it in the video frame with your hands and the full view between windshield a pillars. There are several threads with examples on these boards. I use a small red incandescent light for this. I also have a green incandescent light that comes on when the throttle is pinned wide open. So when I watch the video, I have a clear indication as to when I brake, trail brake and achieve WOT. You can consider this "poorman's data acq.," I consider it enough. With this approach you will have these markers in the video before you do any fancy editing or synching with data, so it is always there for reference if you do not have time to monkey around with all of the other stuff.

3. It looks to me like you were going very easy, which may have lead to a "less known" state of grip in the tyres as you may have not had much feedback on what was available. Then you get into a situation where you think you have plenty of slip for acceleration since you haven't used it all up on cornering... but you are not calibrated as well as you could be, or you get an infusion of BHP from a certain place in the non-linear boost curve.

Again, boost onset must be learned. It is an additional input variable for the driver to deal with that must be managed. There is a reason why Hank Watts says to start with late apexes in a turbo car...make sure you are pointed where you want to go at boost spike.

In my opinion, there are no such things as momentum tracks or cars. We want to go as fast as possible for the minimum lap times, so we want to slow down as little and as infrequently as possible, using all the car has to offer. No getting around that.

5. see next post

5. There is a lot of confusion about the term apex. I try to stick with the definition that involves the widest possible geometric arc, which is always our starting point. Call this geometric apex. If we go earlier, we cannot make the corner, and if we go later, we leave cornering speed on the table.

Now, the actual desired apexes we try to drive often deviate from the engineering drawings of the track. Our cars are not perfect objects of physics and trade-offs are involved. Let's call these desired apexes. Once we know what they are for our car and our circumstances, we try to be within angstroms each and every lap. Not inches, and not feet, not centimeters.

The concept that "earlier apexes can be faster" is rubbish in my opinion. If we achieve higher cornering speed by intersecting the inside of the track earlier, then we made better decisions about the trade-offs. Were were able to achieve this with higher cornering speeds and stayed on the track... great! We made a better set of choices! No confirm and repeat!

I advocate choosing "obviously late" apexes as we learn a new car and/or track. Gives us room to adjust at the exits if we make inappropriate decisions about entry and/or cornering speed, and helps with boost issues.

Sounds like you may have also been getting used to behavior of a different LSD as well. Another variable to learn.

Remember, I know a fair amount about 951 builds... having had several of those cars and being a part of that world for many years. I consulted with some serious pro racers about these cars back in the day, and there haven't been any great revelations since then. Sounds like you are set up for quite a bit of boost. That was never my cup of tea ($$$$).

6. If you had a brake light in the camera FOV I could get a better feel for the timing of brake application going into the corner and once the accident was eminent. I am not sure what you could have done with all of that wet grass,but it looks to me like you did not slow down at all. I assume your foot was planted down on the brake pedal. An unfortunate occurrence at a bad place on the track. Again, maybe it was a set up thing, but I think more likely limits were exceeded in a situation where you weren't pushing and considered yourself well in bounds.

As for 944/951 versus 911 handling, there are lots of ways to compare and contrast. Neither car is inherently faster than the other. Nor brakes better. Depends on the specifics of the car. It is my belief that you drive a car for what it is, and deliver inputs based on feedback and knowledge of what the car is

In my experience, slow in fast out has nothing to do with it. I use that term to discuss trade offs with students... that is what good does it do to lose less speed on entry (brake later or softer or whatever... "faster in") if we get to WOT much later than a "slower entry" approach? I usually say, "when in doubt, slow in fast out."

Again, I hope you mend rapidly and without much discomfort and hassle. When you do get your wheels back together, it might be a great idea to augment on track sorting with some skidpad and/or AX work.

In the engineer's report he says you were going 16km/h faster on that lap at that corner than your previous laps. This tells me that you need to be more gradual in your learning to drive the car fast. It takes alot of track time to get consistant and to develop car control. Just take a more gradual approach to getting faster. The best way to learn car control is to push hard in the slow corners first so you can get used to sliding and catching the car. Then work on the medium corners and finally the fast corners. Until you can enter a turn within 2 or 3 km/hr consistantly you can't push hard in the fast corners.

Once you left the track, there was nothing you could have done differently. Before you left the track the only thing to do was better corrections so as to leave the track pointing straight ahead. This ability will come with more practice at the limit (starting in slower corners).

-Andy

Andy, on face value I can see what you're saying but I have driven that track plenty of times before at similar speeds in the same car (before it was changed). The 16kmh increase was more reflective of the slower previous lap where I was often held up by the car in front more than a sudden ballistic jump in speed. However I'm sure there I'll be a little more careful if I get this repaired and back out there.

Mike, a lot to answer and frankly I'm just a bit too beat to get into it right now, but I do respect your input and am thankful for it. I agree with much of what you've written although would like to continue to discuss one or two facets.

My feeling is that there wasn't 1 single cause for the crash but more likely a combination of 2 or more of these things. Not discounting driver rustiness either.

1) Cold tyres
2) Lack of aero balance
3) Suspension issue. Lack of droop &/or too stiff rear springs
4) Fluid on track
5) Bump in surface
6) Component failure or installation issue

Rough crash man, thats a shame! Just try and stay positive, crashes happen period, best drivers in the world crash, its a risk that comes with what we love to do! I got two Saabs in the junkyard from rally, nothing you can do sometimes

Hope you get back to the track soon!

No sweat.

It is hard to have a conversation on the internet.

It might be helpful to describe and then discuss these things in three basic areas:

The car's changes from what you were used to at this track. For example did you go from a~300 bhp and 3000 pound street/track car on DOT tires to this current car? Since experienced drivers are used to things like changing conditions, and since set-up issues often manifest in several places around a track, many comments and suggestions here have focused on the concept of learning the limits of a new car.

Untoward track conditions. We know the off track conditions were untoward, which really, really sucks. But what about bumps and/or fluids on the track? Did any of your previous forays through that area lead you to believe that something like that was going on?

Problems with car. Set up issues that lead to step function changes like a sudden infinite spring rate or a broken part.

As an aside, I remember back when I installed a Lindsey boost enhancer in my 951. I thought it would be a cheap way to have variable boost, though not cockpit adjustable. I had custom Milledge chips, a shimmed stock wastegate and a drilled factory cycling valve. I installed the new part and adjusted it in street driving to just a tad over the previous boost level, whatever it was-- probably just beyond stock. My idea was that I could turn the boost up a tad bit for timed runs on Sunday.

Well, the car was scary loose on Saturday. Boost onset induced oversteer in several key places around the track. I couldn't do the same lap times as previously because the car was so loose. My co-driver/wife noticed it too. Instantly. She was pissed! So off it came for Sunday. We changed the shape of the curve with that doo dad, and it changed the way the car drove. Turbocharged cars have that extra variable. I sold the gadget to someone with a street-only application. Later I found a pretty much brand new Tial WG on a wreck at Partsheaven. Bought it for $100 (they were as I recall $400 retail at the time) and installed a proper dial a boost set up in the car.

My wife still tells the story of the scary loose car at dinner parties..."my husband is always changing the car..."

Mike, I'm still not sure if you saw the build spec ( http://forums.pelicanparts.com/porsche-autocross-track-racing/661835-my-build-what-its-worth.html ) but this wasn't just a shimmed wastegate upgrade type thing. However the car before was approx 3000lbs with approx 350bhp. Now it's 2600lbs with approx 430bhp. I say approx because the dynos we use are very conservative and it was hp to the wheels. So to get hp to the crank is a matter of debate. I think the factory actually multiplies by 1.32. So we had 360whp which would be more like 385whp on many other dynos. In fact he actually did another pull to show how by merely adjusting the ramp rates and positioning of the car on the rollers could give an immediate increase of 25whp.

So anyway, yes the car has a pretty good power to weight ratio no matter which way you figure it. However it felt generally pretty progressive and not really laggy, laggy, laggy...BANG!!! Also as you can see I am going through a constant radius corner and am virtually floating around there. Again, the Engineer said that I introduced 20% throttle earlier than the previous lap, but I don't think the previous laps are really a good control figure to compare with.

I am hoping we find something that either stands out like dog's bollocks or at least gives us cause to nod and tut tut.
Oh, and yes, there was enough symptoms of irregularity in the setup on previous laps that day. My feeling is that we will turn the boost down next time out and get a more progressive re introduction to the new car.


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Just out of curiosity what made you decide to go with a 900/ 1100 setup for your car? That is def a stiffly sprung car, esp for a car with minimal to no aero

Watching the vid to me that track seems pretty rough, as you track in I noticed your fighting what appears to be the tail starting to step out over some rough parts of your track in, then its kinda hard to tell but it seems like theres a slight crest you rise over as your rear end finally gives out. Stiff springs would def. cause a scenario like this, as your tires start to bounce over these bumps and lose contact with the asphalt your gonna slide, the fact that a 900/ 1100 setup is biased towards a bit of oversteer anyways is gonna make the problemo worse, and if there was a slight crest there like it looks like coming up over that just released the whole monster at once.

Just my .02 cents I would have your engineer look into what natural feq. your running with those springs, IMO 2.5 cycles per second is getting a lil too stiff for a car with no aero, but if your at 3 or over it could def have played a big part

Anyways I hope you get some help from someone on this board, also if you've switch out the tb's for a coilover system I would step down the spring rate

I read parts of that thread. I think you may misunderstand what I am trying to convey about boost. Perhaps we can discuss that further, later.

It is difficult for me to speculate on spring rates since so many variables are involved. I think of the car as a system, and usually seek out professional basic advice from people with experience with my type of car. When I had my 951, I was lucky enough to get some great input (and parts) from Kelly Moss and Jon Milledge. Others as well, plus we had a lot of guys running similar cars so we compared notes. The tracks make a difference as well of course.

Your car would be categorized as a GT car in many forms of club racing here. It is heavy for a GT car. We see a lot of 1900-2300 pound 911s in our area, and they run rates from the 500s to likely near 1K as set up by knowledgeable folks. My car is toward to lower ends of those numbers. To me, a 2600 pound car with the rates you describe could make sense... depends on the types of input one has from others, and so on.

All I can do is basically guess, based on my experience, the video and what you have described. I doubt aero or basic set up would trip up an experienced driver like yourself. Perhaps a new pavement bump with which you were unfamiliar. Perhaps oil or anifreeze-- we always need to watch for that.

To me, unless something broke, it may just be that you exceeded the limits with your right foot, and your opportunity to correct the error was non-existent. And unfortunately the inherent speed in this corner and the off track conditions made the penalty high. Of course these kinds of things happen...

I remember one of my fellow racers with a factory GT3 Cup crashed at 10 at Sears a few years ago. He had a lot of experience and skill, and was level-headed guy. We had gone through there with inches between us many, many times, and I fully trusted him. Then one Friday test day, some guy we didn't know crashes his Cup in 10 and winds up upside down near pit in. Unhurt, but car is totaled. A few hours later, my friend crashes his Cup car into the turn 10 tire barrier and cracks a couple of ribs. Car is totaled. He had just taken out insurance, so he was covered. I have not raced against him since then. They never figured out what caused the crash, but there was speculation that something broke.

Turn 10 is a place where if something goes wrong you can get damage and injury, even if you were only going 5/10s.

Wait a minute.... "hoop spoiler"? Like from a 968?

No rear wing?

Is that correct?

That could be a ginormous ah ha.

Add a large front splitter into the equation....recipe for snap oversteer!! The faster you go the worse it gets.....

Scott

The Motons inc springs were supplied by them in what I was told is their 'kit' for race 951s...but this may have been for their smoother tracks in Europe too. Also, there is a significantly large dual element rear wing to go on the car which we just didn't have time to mount. See pic.
I do think it was more than one issue that caused me to crash but spring rates are certainly being looked into.

I'm sure the spring rates can be applied to this car, but perhaps with some changes...such as going from a hoop spoiler to a proper wing! I'd be happy to discuss boost with you as I'm not quite sure in which way you're referencing it? While I have a bit of experience, I'm no pro. I suspect a bit of rust also contributed to my demise. I'm man enough to hold up my hand on this one. Sounds like there could have been fluid on T10 that day?

While the front splitter isn't huge, I tend to agree that this has added to the mix. Bit of naivete on my part on top of over enthusiasm of getting back on the horse from a long spell.

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Yeah I'd just have your engineer look into what natural frequency those spring rates are giving you! Also I would def suggest getting some track time in an aero car, what a huge difference it is driving a car with significant aero. I remember a few years ago I did the 4 day race course with Bob Bondurant out in AZ and moving into those formula Mazda's just wow, thats all I could say. Its a completely different ball game thats for sure!

Interestingly...or more confusingly, I've just been re-reading a paper prepared by a suspension analysis expert who went over another 951 (which also has all Racers Edge aftermarket components and Moton Clubsports) and who had 800lb springs all round, and his suggestion was to move the rear spring rates up to at least 1200lbs. This car has no added aero nor even a front splitter. He nominated a number of other modifications to be done to help with roll center, bump steer, scrub radius, force application point etc.... The frequency ratings are 3.25hz (f) & 2.34hz (r) with 800lb all round. By moving the rears up to 1400lb which he also didn't rule out, the rear ratings would come up to 3.10hz.

So it's interesting what different viewpoints you can get. The guy spent a full day in the workshop doing all the measurements on this car so it wasn't a cursory glance and pulling figures out of the sky type thing. I'm not saying I'm going to do the same thing btw. Quite possibly the opposite yet this suspension guy would think I'm crazy based on his recommendations.

Before and after shots...http://forums.pelicanparts.com/uploa...1336191967.jpg


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