306 replies to this topic

[Joe Fan]

What is the general consensus about the crash that killed him in the F2 race at Hockenheim. This was a real shocker because Jim was one of the greatest drivers in motorsport history yet there were no skid marks leading up to the tree that he hit. It couldn't have been driver error in my opinion. From what I have read they believe that it was tire or brake related. Does anyone else have any information?

[Huw Jenjin]

Those that should know point to a tyre problem.

[John Cross]

Huw is right - Eric Dymock's book says:

"The most likely explanation was the explosive decompression of a tyre, throwing the car off course and sideways into the fatal tree. The tyre had lost pressure through a slow puncture, and although centrifugal force kept it in shape at speed in a straight line, side force in the gentle curve caused the beading to loosen from the rim and drop into the well".

Both Bob Martin of Firestone and Peter Jowitt of the Royal Aircraft Establishment accident investigation branch examined every shred of evidence and came to the same conclusion.

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I'll be back...

[Keir]

Slowly deflating tire.
Really dangerous at a place like Hockenheim.
I don't believe any other cause was ever
considered.
Jim never made mistakes.

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"I Was Born Ready"

[Jonathan]

A suspension or 'half-shaft' failure have also been discussed as well.

A tire failure is/was thought to be most likely, however.

[Ray Bell]

There was also talk about the possibility that a spectator in a prohibited area ran across the track...

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Life and love are mixed with pain...

[Alfisti]

"Jim Clark never made mistakes"

Pffftt. Obviously Clark was something of a freak talent but everyone makes mistakes.

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"Life will not break your heart, it'll crush it" - Henry Rollins.

[Uncle Davy]

Let's put this one to rest.

Tire failure, right rear...see Appendix Three of Graham Gauld's Jim Clark: The Legend Lives On. Most likely a puncture incurred from debris in the stadium section. I find this explanation the most credible.

[Ray Bell]

Dead right, Alfisti, everybody makes mistakes. Clark bundled up a few cars in his day... they might have been Lotuses, but not all of them went in because something broke.
Come to think of it, would you consider putting you life in the hands of Lotus a mistake? Many did...

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Life and love are mixed with pain...

[Don Capps]

Clark was human and made a few mistakes on the track, but very few. And he was always willing to admit them.

The Firestones used in 1968 gave little warning and minimal feedback when losing compression, especially at high speed. The tire went and when the Lotus left the road, Clark never had a chance. All the other tales were exactly that.

Ditto the fate of Alberto Ascari -- the lousy Engelberts on the Ferrari he was driving at Monza failed and that was fini for poor Alberto. Unless Karl has some new information I am unaware of, that was what ended up killing Ascari in my opinion.

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Yr fthfl & hmbl srvnt,

Don Capps

Semper Gumbi: If this was easy, we’d have the solution already…

[Vicuna]

All will be revealed in September of this year.

I promise.

Never before heard shared evidence.

[Joe Fan]

Originally posted by Vicuna
All will be revealed in September of this year.

I promise.

Never before heard shared evidence.

Any chance we can know where to keep our eyes pealed?

[DOHC]

Originally posted by Vicuna
All will be revealed in September of this year.

I promise.

Never before heard shared evidence.

And why only in September? The accident took place over 35 years ago. What is it that can be told in September but not in May?

[Vicuna]

It's a hard secret to keep but I promise to tell you where to keep your eyes peeled.

[Mickey]

You got my attention, allright

[BorderReiver]

And mine

[David Beard]

Can anyone recall how Clark's accident was described in Derek Bell's biog? When I read it some years ago I wasn't sure what was being suggested.

[D-Type]

Originally posted by Ray Bell
There was also talk about the possibility that a spectator in a prohibited area ran across the track...

Wasn't that Ascari? It is mentioned and discounted in Ferrari's autobiography "My terrible style", or rather "My terrible joys".
Incidentally in "Challenge me the race" (an equally stupid book title), Mike Hawthorn gives a plausible explanation for Ascari's accident . It was a mismatch of tyre size and rim size that made it possible to rip the tyre off the rim.

[i]Originally posted by Vicuna[i]
All will be revealed in September of this year.

I promise.

Never before heard shared evidence.

I'll guess that the full statement of the German marshall will be published.

[i]Originally posted by Alfisti[i]
"Jim Clark never made mistakes"

Pffftt. Obviously Clark was something of a freak talent but everyone makes mistakes.

But not on this occasion. His fatal accident was definitely due to tyre failure. At that time the expert opinions would have been honest and not influenced by "spin".
Although he had some accidents in his career, the number was far fewer than his contemporaries and I cannot recall any that were attributed to driver error.

[Joe Fan]

Originally posted by D-Type

But not on this occasion. His fatal accident was definitely due to tyre failure. At that time the expert opinions would have been honest and not influenced by "spin".
Although he had some accidents in his career, the number was far fewer than his contemporaries and I cannot recall any that were attributed to driver error.

On a similar thread, Ralliart posted a piece where Fred Gamble believed the crash was not due to a tire failing because he got to look at the aftermath and the tires. This steers it towards suspension failure, if driver error is totally ruled out. I have huge respect for Gamble's opinion. For my Masten bio, he sent me a seven or eight page typed letter (single-spaced!) about the Camoradi team and he demonstrated excellent memory of facts forty years ago. He also struck me as someone who told it like it was, not someone who told things in a phoney politically correct manner. This coupled with the knowledge of Chapman's fragile designs makes me believe it was suspension failure.

[D-Type]

Joe fan,
I won't argue very strongly against suspension failure but I will argue until the cows come home and carry on until they go out again that it was NOT driver error

[Joe Fan]

Originally posted by D-Type
Joe fan,
I won't argue very strongly against suspension failure but I will argue until the cows come home and carry on until they go out again that it was NOT driver error

Well, I don't think it was driver error either for several reasons. First, the location of the accident. Second, driver error is often over assumed with accidents in the first place by fans and pundits. It is the easiest explanation. However, when you are dealing with talented and experienced professional drivers, the vast majority of the time, accidents are due to something breaking on the car--especially if they knew the car and the circuit well.

[Vicuna]

It wasn't driver error

[Milan Fistonic]

Originally posted by David Beard
Can anyone recall how Clark's accident was described in Derek Bell's biog? When I read it some years ago I wasn't sure what was being suggested.

Bell believed that a misfire was the cause of Clark's accident. He remembers Clark's mechanic driving the Lotus up and down the paddock on race morning trying to cure a misfire.

"I think Jimmy was having a terrible time with that misfire. Running alone, battling with a poor car on tyres which were not working terribly well, I reckon the engine suddenly cut out. He would have automatically applied a touch of opposite lock as the car began to slide - and then the power came back on, the rear end gripped, and the car suddenly speared off into the trees on the left of the track. In my mind thre's just no doubt about it. That's how Jimmy died."

[Roger Clark]

I can only say that Peter Jowitt who conducted te technical examination of Clark's car after the crash was a senior engineer at the Experimental Aircraft Department at Farnborough. He specialised in milatary prototype aircraft accidents and was highly experienced at this kind of technical analysis. He wrote:

"We had a piece of evidence of enormous value. A statement had been taken from the marshal who had been very nearly hit by the car, and it had been taken while he was white-lipped and trembling, and before he had time to rationalise. He said that he had seen the car, whilst coming towards him, start to break away at te rear end. There had been a correction which caused a sharp breakawy the other way, followed by another correction which caused a further, fairly gentle but progressive breakaway in the original turning left mode, which continued until the car hit the tree.

"Any oversteering accident will focus attention on the rear of the vehicle, and I found an odly shaped cut in the tread of te right-hand rear tyre. This cut went completely through the tyre, and I could not find any part of te wreckage which could have caused it. If te tyre had been punctured, there is an odd effect which I had seen before. At high speed in a straight line, centrifugal force will in fact hold the tread out so that it looks as if there is no puncture and the driver will not know that the tyre has deflated.

"As soon as a side load is put on, in cornering, the tyre becomes unstable, and cannot generate the cornering force the driver would expect. With the right-hand tyre deflating, the effect in a right-hand corner would be some oversteer, Correcting this by steering left would put a heavier cornering load on to the unstable right-hand tyre, which would give rise to vicious right-hand oversteer. Correction in the opposite sense, at high speed on a very wet track, would clearly be difficult. The tachometer in the car, a mechanical type, indicated that Jim had the power on right up to impact, clearly trying to hold the car. There are however, situation when even the unearthly skill of Jimmy Clark will not suffice."

I don't think this is a man who would tell things in a phoney politically correct manner.

[Doug Nye]

Absolutely. I believe the real mystery about Jimmy's accident is why people keep revisiting it as a mystery... It was a tragedy which in some way - sometimes major, sometimes minor - reshaped thousands of enthusiasts' lives thereafter.

DCN

[Joe Fan]

Originally posted by Roger Clark
I can only say that Peter Jowitt who conducted te technical examination of Clark's car after the crash was a senior engineer at the Experimental Aircraft Department at Farnborough. He specialised in milatary prototype aircraft accidents and was highly experienced at this kind of technical analysis. He wrote:

"Any oversteering accident will focus attention on the rear of the vehicle, and I found an odly shaped cut in the tread of te right-hand rear tyre. This cut went completely through the tyre, and I could not find any part of te wreckage which could have caused it. If te tyre had been punctured, there is an odd effect which I had seen before. At high speed in a straight line, centrifugal force will in fact hold the tread out so that it looks as if there is no puncture and the driver will not know that the tyre has deflated.

Here is a copy and paste from that old thread where Gamble gives his opinion:

Fred Gamble, who, as of May 1993 resided in Snowmass, Colorado, wrote to ON TRACK magazine and, in the 23 May '93 issue, his letter - headed "Time For The Truth" - was published. gamble had this to say:
"Concerning the circumstances of Jimmy Clark's death...maybe it is time the truth is told. I was privileged to be a part of that era and a friend of Jimmy's, so was just as devastated as everyone else when he was killed. His car had a rear suspension failure; sadly one of the frequent and well-known results of the brilliant but fragile Lotus cars of that era. I was Goodyear's first director of international racing at the time and, as Firestone was contracted to Lotus, after the accident and rumors of a tire failure, Firestone engineers showed me the tire off the Clark car, not deflated or failed, but obviously dragged sideways after a suspension failure. Jimmy would have had a chance of dealing with a puncture and deflation but suspension failure, no way could he have controlled the car. I can understand Firestone not wanting to 'blame' Lotus car failure because of their corporate relationship with Lotus and Colin Chapman...I think those of us in the sport at the time who knew the details of Jimmy's death have probably kept quiet out of respect for Colin Champam's brilliance as a designer, but more because the great Jim Clark was like a son to Chapman. I'm sure Chapman knew the cause of the accident but to have been publicly condemned for a fragile design failure might have been emotionally too much for Colin to bear."

Since Gamble was a Goodyear tire director and the tire in question was a competing Firestone brand, I would put more stock in what Gamble says that the cut in the tire was from being dragged sideways after suspension failure. I also think Gamble made several other good points. Jim was like a son to Colin and also agree that many probably would keep quiet or not press the suspension failure theory. This was also before the outcry of safety and motor racing was accepted as a very dangerous daredevil-like sport. Had this happened today, Chapman and his designs would have been heavily scrutinized and raked over the coals like Frank Williams was when Senna was killed.

[Mike Argetsinger]

Originally posted by D-Type



I'll guess that the full statement of the German marshall will be published.


But not on this occasion. His fatal accident was definitely due to tyre failure.

The marshal you refer to is Winfried Kolb. He was the sole eye witness to the crash. He was manning the outpost alone and observed the car approaching him, passing by him and crashing. He gave his official report to Race Director Leopold Baron von Zedlitz. It was transcribed on the spot by Werner Winter, a member of the organizing team for the Wiebaden Automobile Club, and filed with the Automobil Club von Deutschland (AvD). Copies were mailed to Colin Chapman and Graham Hill. It has never been suppressed - then or now. So there has never been a "full statement" that has not been published. That is not to say that Mr. Kolb may not have subsequently been interviewed by someone else - this may be what you are suggesting - I don't know. But I can say with certainty that his original and full report was recorded at the time and it has always been available.

Incidentally, Mr. Winter recently gifted to the International Motor Racing Research Center (IMRRC) at Watkins Glen his entire archive of the weekend including the original transcript and other materials pertaining to that race meeting.

I totally agree with your statement regarding tire failure as the culprit. There is no mystery here - only a remaining sadness.

[tombe]

Originally posted by Vicuna
All will be revealed in September of this year.

I promise.

Never before heard shared evidence.

Publishing date for Eoin Young's Amon biography is september.
And Amon was in that race...........

[Dennis Hockenbury]

For me, the cause of Jim Clark's death at Hockenheim is of no real consequence 35 years on. The 15 year old fan lost his first, and possibly last, true driving hero.

The manner of his death pales in comparison to the magnitude of his loss to a generation.

And he is still missed by the 15 year old boy deep inside the 50 year old man.

[Ralliart]

Joe Fan, I was the "someone" who posted the piece by Fred Gamble...

[Ruairidh]

Originally posted by Dennis Hockenbury
For me, the cause of Jim Clark's death at Hockenheim is of no real consequence 35 years on. The 15 year old fan lost his first, and possibly last, true driving hero.

The manner of his death pales in comparison to the magnitude of his loss to a generation.

And he is still missed by the 15 year old boy deep inside the 50 year old man.

You have captured exactly my thoughts and emotions.

[Ruairidh]

Originally posted by Joe Fan


Here is a copy and paste from that old thread where Gamble gives his opinion:

Fred Gamble, who, as of May 1993 resided in Snowmass, Colorado, wrote to ON TRACK magazine and, in the 23 May '93 issue, his letter - headed "Time For The Truth" - was published. gamble had this to say:
"Concerning the circumstances of Jimmy Clark's death...maybe it is time the truth is told. I was privileged to be a part of that era and a friend of Jimmy's, so was just as devastated as everyone else when he was killed. His car had a rear suspension failure; sadly one of the frequent and well-known results of the brilliant but fragile Lotus cars of that era. I was Goodyear's first director of international racing at the time and, as Firestone was contracted to Lotus, after the accident and rumors of a tire failure, Firestone engineers showed me the tire off the Clark car, not deflated or failed, but obviously dragged sideways after a suspension failure. Jimmy would have had a chance of dealing with a puncture and deflation but suspension failure, no way could he have controlled the car. I can understand Firestone not wanting to 'blame' Lotus car failure because of their corporate relationship with Lotus and Colin Chapman...I think those of us in the sport at the time who knew the details of Jimmy's death have probably kept quiet out of respect for Colin Champam's brilliance as a designer, but more because the great Jim Clark was like a son to Chapman. I'm sure Chapman knew the cause of the accident but to have been publicly condemned for a fragile design failure might have been emotionally too much for Colin to bear."

Since Gamble was a Goodyear tire director and the tire in question was a competing Firestone brand, I would put more stock in what Gamble says that the cut in the tire was from being dragged sideways after suspension failure. I also think Gamble made several other good points. Jim was like a son to Colin and also agree that many probably would keep quiet or not press the suspension failure theory. This was also before the outcry of safety and motor racing was accepted as a very dangerous daredevil-like sport. Had this happened today, Chapman and his designs would have been heavily scrutinized and raked over the coals like Frank Williams was when Senna was killed.

Is it just me who cannot reconcile what I remember of the Jowitt investigation and the quote attributed to Gamble above? Are we meant to believe that Jowitt was either (a) incompetent or (b)covering up for Lotus?

[DOHC]

Originally posted by Dennis Hockenbury
For me, the cause of Jim Clark's death at Hockenheim is of no real consequence 35 years on. The 15 year old fan lost his first, and possibly last, true driving hero.

The manner of his death pales in comparison to the magnitude of his loss to a generation.

And he is still missed by the 15 year old boy deep inside the 50 year old man.

Spot on. I was also 15 and felt/feel the same.

[Joe Fan]

Originally posted by Ruairidh
Are we meant to believe that Jowitt was either (a) incompetent or (b)covering up for Lotus?

No. Jowitt's opinion is an opinion just like everyone elses. His specialty was aircraft accidents. If Clark had been on the same set of tires for a long time, I would give more credence to the tire failure theory. However, Clark crashed on what, lap 5 or 6? How probable would it be for a major tire failure so early in a race? The cut in the tire either had to be due to one of three things: 1) a major tire failure, 2) due to running over a significant piece of debris, or 3) cut during the accident.

Originally posted by Ralliart
Joe Fan, I was the "someone" who posted the piece by Fred Gamble...

Sorry for having not given you the credit of posting that.

[Doug Nye]

The engine and rear suspension wreckage of Clark's car after the Hockenheim accident - note the deflated rear tyre with its beads popped off the wheel rim ledges into the wheel's centreline well.

This certainly sometimes happened to these unrestrained-bead tubeless tyres in an accident after deflation caused on impact.

But it is also consistent with the belief that as the punctured and deflating tyre had lost pressure, and the car continued to run at very high speed, so this tyre's pressure had fallen below the critical level at which it was sufficient to keep the tyre walls and beads apart, secure on their ledges despite centrifugal 'throw-out' of the centre-tread tyre crown seeking to draw those beads inwards.

As that critical minimum low pressure point - keeping the tyre in shape - was passed, so 'throw-out' was sufficiently strong to draw the tyre's beads inwards, permitting them to pop into the wheel's centreline and creating an explosive decompression of what air-pressure remained within the tyre. The effect would have been an instantaneous tyre collapse and loss of any adhesion.

Not proof - but powerful circumstantial evidence consistent with Peter Jowitt's conclusion. And Jowitt's opinion absolutely is NOT " an opinion just like everyone elses ". Give us a break....

Oh I haven't added that in addition to being an aeronautical engineering and accident analysis inspector by profession, Peter was also a fully-authorised, experienced and highly competent RAC motor sports scrutineer... His particular expertise absolutely bridged the disciplines, not that there was/is much of a gulf to bridge.

DCN

[David McKinney]

Originally posted by Joe Fan

No. Jowitt's opinion is an opinion just like everyone elses. His specialty was aircraft accidents.

Which sounds very much to me as if you are saying he was incompetent to form an opinion. Not the sort of judgment I would have thought should be levelled at a man who had, at that time, investigated probably as many motor racing accidents as anyone else, and whose views were highly respected by the racing establishment

[Catalina Park]

The evidence of a tyre deflation at speed is lots of rubber marks on the wheel from the tyre rubbing on it and I am sure that this was what was found on the rear wheel of the Lotus.

If the tyre was knocked off its beads during the crash it not have left the same sort of marks.

[Joe Fan]

Originally posted by David McKinney

Which sounds very much to me as if you are saying he was incompetent to form an opinion. Not the sort of judgment I would have thought should be levelled at a man who had, at that time, investigated probably as many motor racing accidents as anyone else, and whose views were highly respected by the racing establishment

David,

How can you say that? Everybody's opinion is still an opinion, some more educated than others but still an opinion. Why? Because nobody knows with 100% certainty what actually happened. You can narrow it down to a few probable causes but it is difficult to ascertain whether some things were a cause of, or result from the accident.

[Joe Fan]

Here is another question to ponder: If Clark's crash was due to a tire defect, and if Jimmy was like a son to Colin and he knew the crash was due to defective tire, why would Colin stick with Firestone tires until the 1973 season when he could have easily switched to Goodyear? Common sense or emotions would tell you that he would have switched to different tire for the 1969 season.

[David McKinney]

1) Roger quoted Jowitt giving a view
2) By posting the Gamble comments you seemed to be challenging this view
3) Ruairidh raised the question of this conflict of views, suggesting that if Gamble was to be believed, then Jowitt was either incompetent or covering for Lotus
4) Your comment, which I quoted, suggests that you regard Jowitt's opinion as no more valuable than anyone else's - in other words, he was no more competent than anyone else to form a view
5) My post (which I sent before I had read Doug's) was intended to show that this demeaned Jowitt's standing (and his opinion, and his competence)
6) and a new point - I would expect a tire company PRO to defend his industry, whereas I would expect an accident investigator to be independent

[Joe Fan]

Originally posted by David McKinney
1) Roger quoted Jowitt giving a view
2) By posting the Gamble comments you seemed to be challenging this view
3) Ruairidh raised the question of this conflict of views, suggesting that if Gamble was to be believed, then Jowitt was either incompetent or covering for Lotus
4) Your comment, which I quoted, suggests that you regard Jowitt's opinion as no more valuable than anyone else's - in other words, he was no more competent than anyone else to form a view
5) My post (which I sent before I had read Doug's) was intended to show that this demeaned Jowitt's standing (and his opinion, and his competence)
6) and a new point - I would expect a tire company PRO to defend his industry, whereas I would expect an accident investigator to be independent

David, Fred Gamble was not on Firestone's payroll, he was a Goodyear rep. And what would he have to gain in covering up for an industry when his comments were first published in 1993, 25 years after the fact? And as I stated in my last post, why did Colin stick with Firestone tires until the 1973, if he knew, or had a high suspicion, that the accident was due to a defective tire? Jowitt's investigation did not occur at the scene. And it was not an independent investigation. He was hired by Chapman to conduct the investigation. So whose opinion would you put more stock in? With the all the above in mind, I will put more stock on Gamble's opinion because he had nothing to gain.

[Doug Nye]

Originally posted by Joe Fan
Here is another question to ponder: If Clark's crash was due to a tire defect, and if Jimmy was like a son to Colin and he knew the crash was due to defective tire, why would Colin stick with Firestone tires until the 1973 season when he could have easily switched to Goodyear? Common sense or emotions would tell you that he would have switched to different tire for the 1969 season.

The words 'straws', 'at', and 'grasping', spring to mind here....

Nobody with any sense concluded the tyre was 'defective' - Peter Jowitt located a puncture in it.

And if you think Chunky would ever have dropped a cooperative manufacturer of quick tyres just because anybody might have died using them you plainly haven't yet grasped what ACBC was all about...

DCN

[Joe Fan]

Originally posted by Doug Nye


Nobody with any sense concluded the tyre was 'defective' - Peter Jowitt located a puncture in it.

And if you think Chunky would ever have dropped a cooperative manufacturer of quick tyres just because anybody might have died using them you plainly haven't yet grasped what ACBC was all about...

DCN

Doug,

Then why does Jowitt say this:

"Any oversteering accident will focus attention on the rear of the vehicle, and I found an oddly shaped cut in the tread of the right-hand rear tyre. This cut went completely through the tyre, and I could not find any part of the wreckage which could have caused it. If the tyre had been punctured, there is an odd effect which I had seen before. At high speed in a straight line, centrifugal force will in fact hold the tread out so that it looks as if there is no puncture and the driver will not know that the tyre has deflated."

[Doug Nye]

Comprehension? I suggest you carefully read again what Peter wrote...take care now...

DCN

[Joe Fan]

Originally posted by Doug Nye
Comprehension? I suggest you carefully read again what Peter wrote...take care now...

DCN

Doug,

I am not suggesting Jowitt is claiming a tire defect but he does say that there was no puncture in the right rear tire; he in fact says that there was a cut in the tire. Now this means that the cut was either due to: 1) running over debris or 2) due to a tire defect.

[Geoff E]

Originally posted by Joe Fan
I am not suggesting Jowitt is claiming a tire defect but he does say that there was no puncture in the right rear tire; he in fact says that there was a cut in the tire. Now this means that the cut was either due to: 1) running over debris or 2) due to a tire defect.

The word "cut" to me (in relation to tyres, but actually in relation to everything on second thoughts) implies damage by some sharp external agent.

[Doug Nye]

No - no - no - Joe - no.... Peter Jowitt reported "This cut went completely through the tyre"...

It was a TUBELESS tyre.

Cut going completely through Tubeless Tyre = puncture...

And he did NOT say "that there was no puncture in the right rear tire..." (your quote), he said "At high speed in a straight line, centrifugal force will in fact hold the tread out so that it LOOKS as if there is no puncture and the driver will not know that the tyre HAS DEFLATED."

Much more of this Fan and you might have to stay behind after school.

DCN

[Joe Fan]

Originally posted by Doug Nye
No - no - no - Joe - no.... Peter Jowitt reported "This cut went completely through the tyre"...

It was a TUBELESS tyre.

Cut going completely through Tubeless Tyre = puncture...

And he did NOT say "that there was no puncture in the right rear tire..." (your quote), he said "At high speed in a straight line, centrifugal force will in fact hold the tread out so that it LOOKS as if there is no puncture and the driver will not know that the tyre HAS DEFLATED."

Much more of this Fan and you might have to stay behind after school.

DCN

Doug,

Where was this cut at? In the sidewall or on the tread?

[Geoff E]

Originally posted by Joe Fan


Doug,

Where was this cut at? In the sidewall or on the tread?

"an oddly shaped cut in the tread of the rear right-hand tyre. The cut went completely through the tyre and I could not find any part of the wreckage which could have caused it."

(Which is actually what DCN said a few posts ago, but I have just copied it from my book.)

[Dennis Hockenbury]

A passage from Jim Clark, Graham Gauld, Pg 84:

"There is no doubt in Colin Chapman's mind as to the cause of the accident: 'it was a puncture of the rear right tyre'. At the same time he is convinced that it was such a freak accident that it might only have happened on a circuit like Hockenheim. He reconstructs the accident in the following way. 'Jimmy probably picked up something in the tyre on the fourth lap.' (In practice the previous day, Walter Habegger had broken the crankshaft of his car, and a small fragment of metal may have been lying on the road.) It didn't need much loss of pressure for the effect to be felt and, when Chark started to go through the twisting piece of track in front of the grandstands, the rear-tyre pressure was possibly down from 15 psi to 10 psi. When he reached one sharp left-hand bend a fellow driver saw him slide an then quickly correct it. As the next corner was a sharp right -hander, the weight of the car would be thrown on the the left-hand side and away from the right rear tyre, and it assumed that Jimmy put his trouble at the previous bend down to the greasy surface of the track. Even if the pressure had dropped to 8 psi, the tyre would have stayed on the rim as it was a slow right-hand corner. However, once he opened out to the back straight, the steadily rising speed, and the steadily deflating tyre brought the power of centrifugal force into play. In tests following the accident it was found that, under these conditions, the tyre would begin to grow and at a crucial point the sidewalls would be drawn in, and there would be an explosive depressurisation as the the air rushed out. From that moment, an accident was inevitable."