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BRM P25


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#1 Wolf

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Posted 09 November 2000 - 01:53

I'm at loss whether this thread would be more approppriate over on TTF or here, but the dice has fallen. Jo Bonnier has said that it was 'the most beautiful looking race car of all time'. Re-reading RVM on '59 season one thing sprung to my attention. Don wrote:
An unusual aspect of the BRM design was that there was only a single rear disc brake, which worked off the end of the rear-mounted transmission. Unorthodox and clever, it was also a point of concern, having not been very good at its job over time.
I belive this disc can be nicely seen on this photo (whilst at it, my uneducated guess would be that the other driver is McLaren- 8W players take the stand).
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That braking method has crossed my mind before (of course, I was totaly unaware that such thing did exist, which proves my ingenuinity and brilliance [Applause. Cheers from the audience.]). Needless to say, I was almost tarred and feathered for having such preposterous ideas:). Well, I myself had some doubts on that matter and I would like to share them with you. In my opinion P25 had to be basically oversteering car- can anyone prove me right or wrong?
Here's why I assumed it- single brake must have been mounted before the differential in order to brake on both wheels. And in that case braking force was distributed on the wheels as is driving force- better braking on inner wheel (for it revolves more slowly). This manner of braking induces understeering. So, if P25 was already understeering car, this feature would seriously impair it's performances. The other issue is if car is oversteering, in which case braking in the curve induces drift. Am I right?
The issue that I almost got flogged about is that I was speaking of installing such thing in normal car. And there's a fine difference because people usually brake in the corners when things start to get out of hand. And this brake would make the things even worse.

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#2 oldtimer

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Posted 09 November 2000 - 02:58

Hi wolf, it's me again!

The BRM 3 brake system lasted from 1955 to 1960 (in the rear-engined cars). Those were not the days of sponsorship, and building new components for each season was not on.

The brake system caused lots of problems, and possibly lost BRM two championship races, Behra at Monaco in '58, and Graham Hill in his famous drive from last to first at Silverstone in '60. Behra ran out of brakes, and Monaco was the last place you wanted to do that before the days of armco. Hill was having to pump his brakes with a very determined Brabham in his mirrors, having overhauled the whole field. Passing Brabham was could be one thing, getting away from him another. Anyway, Graham left the pumping a bit too late and ended in the ditch at Copse, spoiling what would have been a classic drive.

Back to Goodwood in 1957 (oh no, not again you say!), the brakes were locking on and not releasing during practice! The BRM team was a total shambles. Salvadori (no.1 driver)got so pee-ed off, he went off to find somebody's Cooper to drive during the session. "Where's Salvadori?" asks Raymond Mays. "On the track," was the reply, "In a Cooper."

And then Behra had to use the wall at the Goodwood chicane to stop himself in 1958 after a total brake failure going into Woodcote. Left him wondering how fast he could take Woodcote under control!

The P25 looked very stable on the track, with a mild understeer. By all accounts, a nice car to drive.

And, oh yes, that man, SM lost all his brakes in the International Trophy at Silverstone in 1959 whilst in a works P25. Remember a lovely picture of him in MS preparing to make a crash landing in a ditch.

#3 Ray Bell

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Posted 09 November 2000 - 08:27

Providing the diff was doing its proper limited slipping, and the traction was good, I don't think it would have made any difference. Am I right in recalling that the failures were fractures in the inflexible lines?
Of course, it's anyone's guess what the locking on was...
A picture of the rear of the rear engined car shows it much better, and I think there's one been used somewhere on the forum.

#4 Ray Bell

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Posted 09 November 2000 - 08:31

Whoops... sorry, forgot about the Cooper. Not McLaren, I don't think. Moss doesn't mention McLaren in the race, but does mention Gregory... where's Joe Fan.
The hat's too dark for McLaren, who had a silver one those days, like Jack. None of this is conclusive, though, and Moss' story is hardly a complete report. But I'll plump for Gregory.

#5 Rainer Nyberg

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Posted 09 November 2000 - 10:04

The 1960 BRM P48 offers a better view of the single-disc brake arrangement.

Graham Hill with his car at Monza.

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Rainer

#6 Racer.Demon

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Posted 09 November 2000 - 11:02

BRM's peculiar brake solution for the P25 was the car's foremost reason of failure, causing many hairy moments, such as Hans Herrmann's monumental flip at Avus '59.

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Centering around Bonnier's classic Zandvoort win (that's Brabham in Wolf's picture, BTW) my friend Felix wrote a nice story on BRM's poor early form. You can find it in the October '99 issue of 8W:

http://www.racer.dem...8w/8w-1099.html

Read it and you'll notice that those brakes just kept on harrying Messrs Mays and Berthon!


#7 oldtimer

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Posted 09 November 2000 - 20:15

If THE thread can rustle up Chris Amon, can anyone out there rustle up Dan Gurney to comment on the 1960 BRM's brakes?

#8 Roger Clark

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Posted 09 November 2000 - 20:16

Most of the BRM brake failures described above were due to the servo and associated hydraulics and not to the single rear disk. THey had some initial problems, caused by the fact that the disk was rotating much faster than normal and therefore the rubbing speeds were very high. Once those were sorted, the single disk gave no problems.

#9 Ray Bell

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Posted 09 November 2000 - 20:19

Gurney, yes, Gurney... was it the reason for him going off at Zandvoort.
Can't have been too bad, neither of them went off the road at Warwick Farm, and you needed brakes there. The just melted the glue in their fuel tanks with the heat, I think it was... strange reason for a team to go out.. but then the history of racing is dotted with many strange reasons.

#10 Mike Argetsinger

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Posted 09 November 2000 - 22:31

Tony Rudd, in his book "It Was Fun - My 50 Years of High Performance," has the following to say about the cause of Dan Gurney's crash at Zandvoort in 1960:

"On the 10th lap the special aircraft pipe to Dan's rear brake burst as he was going in to the hairpin at the end of the main straight."

This account matches up with Roger Clark's observation (above) that most of the BRM brake problems were due to the servo and associated hydraulics.



#11 Wolf

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Posted 09 November 2000 - 23:43

Just occured to me that it might have had something to do with cooling of the brake; and that could also account for reliability problems.
BTW, I'm going to take that offer on 'Design & Behaviour ...', maybe there will be something in there.

#12 Ray Bell

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Posted 10 November 2000 - 00:03

If there is, I think it will only be mentioned in passing, it wasn't, from memory, one of the cars Moss relied on for a season and therefore wasn't in the book. But I may be wrong, it's been gone a long time.
As for the heat, it was all hydraulics, the problems, but you may be right, maybe some vapourisation.

#13 desmo

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Posted 10 November 2000 - 01:32

I still don't see anything intrinsically wrong with the concept. Benetton's somewhat similar ill-fated FFT system from last year was more an execution and mass problem than a problem with the concept of using a torque splitting diff to transfer braking torque side to side. Makes more sense to me in the rear where the pieces are already there. It would definitely reduce unsprung weight.

#14 Wolf

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Posted 10 November 2000 - 02:35

And here's another technical aspect- because of additional forces (vertical in particular), axles have to be heavier (additional stresses which are result of braking forces) and, IMHO (because of braking momentum), additional stiffnes wouldn't hurt.

#15 Ray Bell

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Posted 10 November 2000 - 02:51

Less overall weight, too.

#16 oldtimer

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Posted 10 November 2000 - 03:57

The weight factor was the driver in the BRM design, I believe.

Roger, the Mays and Roberts book reports the servo system being removed after the 1958 Goodwood meeting. Whereas it caused Behra to lose his brakes, it caused a locking problem with Schell's. The litany of brake problems still continued though.

I've always wondered if the one brake doing the work of two imposed stresses on the hydraulic system that BRM could not manage. Problems never seemed to go away.

Did the drivers have to nurse the brakes?


#17 desmo

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Posted 10 November 2000 - 07:00

If weight was a real concern why on earth are they using such ridiculously long spring/damper units? Look at the number of coils in those springs. It would be easy using only the technology of the day to design a suspension that would yield the same wheel travel and spring rate without theose massive looking spring/damper units.

#18 Roger Clark

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Posted 10 November 2000 - 19:38

I think a large part of the problem was vibration from the short stroke 4-cylinder which caused pipes to fracture.

#19 oldtimer

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Posted 10 November 2000 - 20:10

The original car had air-struts front and rear. The coil spring units were a later addition, rear in '57, and front in '58. The air strut cars were unstable at the front under acceleration, which made for exciting viewing when Hawthorn was driving the '56 version. He was quite prepared to fight it so he could enjoy the acceleration, which was the car's strong point.

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#20 oldtimer

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Posted 11 November 2000 - 07:52

Skim reading often leads to corrections! Both front and rear suspensions were changed to coil spring systems in 1957 from leaf (rear) and air struts (front). The change to coil springs meant a whole new sub-frame was needed at the rear, changing the appearance of the car. A new sub-frame for the front was installed in 1958.

The '58 car was radically different from the original concept, looking, and presumably being, bulkier, though my sources don't give any comparative data for weights.

#21 PDA

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Posted 12 November 2000 - 01:17

A recent article in Motor Sport (the anniversary issue) shed some light on the single rear brake issue. The reporter cites Rudd as sayoing that it gave problems due to heat and also becsause of the vibration caused by being on the gearbox main shaft, at the end of a rather long prop shaft. The vibration backed of the pads, meaning that pumping was regular. Also the vibration frequently broke the fluid feed pipe, which was originally a solid pipe.

The argument given above that they couldn;t replace components each season has validity, but to keep this abomination for 6 years, essentially unchanged, was economy gome mad. When Rudd took charge for 61, it went. One can only presume that the idea was retained on the basis of reduced unsprung weight. The fact of the matter is that the theoretical advantages were outweighed (in most peoples minds (particularly the drivers)) by hte unreliability it introduced.

With regard to handling, it is probably safe to assume that the later P25 was designed to understeer as a basic feature. It was designed by Chapman while he was still under the influence of the standard thinking introduced by the MB engineers in the late thirties - basic understeer for stability, with power induced oversteer creating the 4 wheel drift. h Chapman persisted with this in all of the designs he was involved in (P25, Vanwall, Lotus 16) until it became clear that with the power outputs then available (250 hp cf 500+ for the MB 154) the understeer sapped too much power. this was ably demonstrated by Cooper, and once Chapman overcame his revulsion of "copying), the Lotus 18 proved the fastest car on the grid.



#22 oldtimer

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Posted 12 November 2000 - 02:15

Chapman didn't redesign the P25. He drove the car, and strongly recommended the use of coil springs front and rear and changes in the de Dion system. BRM did the design of the sub-frames and new rear suspension.

Mays reported that Behra had quite a hand in making recommendations for the front end. I get the impression that BRM were having to chase some major chassis design short-comings in the '56 car, rather than pursuing a design intent. 'Make it driveable' seemed to be the quest, and they succeeded.

#23 PDA

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Posted 13 November 2000 - 06:06

The BRM drawing office may well have done the drawings, but I suspect that Chapman gave more than suggestions for his consultancy fee. The back suspension looks suspiciously like Chapman strut from the photograph.

#24 oldtimer

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Posted 14 November 2000 - 03:58

Indeed yes, PDA. Chapman used a similar system in his design of the Vanwall chassis.

I want to thank Felix for e-mailing me copies of his, and Don's, articles on the BRMs. He that rules most things in the computer world had decreed that I cannot access the Demon-racer's link, and Felix responded very quickly to my request. Linking to another thread, it goes to show, again, what a fine thing you have started Don, and what a great bunch of people support this forum.

One of the things that struck me about this thread was the difficulty some people were having relating to why BRM stuck with a braking system that caused so much trouble, and why they contradicted the early chassis design principles of the car.

Some of the reasons are hard to understand from a current viewpoint of F1 racing, when new chassis' are built every year. The '50's were not the times of the big spenders, and even Tony Vandervell used major components from the earlier cars when Chapman designed a new chassis for the 1956 season.

I am not a F1 historian, but trying to look at 1950's cars from the 21st century is not easy, and the record books and specification tables don't capture the whole story.

Now I have not been a good historian (sorry !)in examining all my sources re the chassis/brake issues before making posts. They are DSJ's Racing Car Reviews for 1956,'57, and '58, the Mays and Roberts' book.

The chronology they show is:
1955: Short chassis (7ft 3in. wheelbase), air struts front & rear
mid-1956: chassis lengthened by 3in
Sept.1956: Double stressed skin applied around cockpit area, air struts at rear replaced by leaf spring.
1957,mid-season: coil spring units used front & rear, rear chassis redesigned.
1958: new chassis, stressed skin structure eliminated. Servo removed from braking system after Goodwood meeting.

Now all this says to me that the original chassis, as well as the suspension and braking system, were pretty deficient when compared to the opposition, and the chaps in their tweed jackets were pretty slow in coming to terms with the problems.

The original engine was another matter, as anyone witnessing Hawthorn jack rabbit away from all the opposition at Silverstone in 1956 could testify. The engine was designed to run at 9000rpm, but at Monaco in 1956, they discovered that large valves were being distorted by temperature gradients. Redesign was necessary, and it took 2 years to get maximum revs up to 8,250rpm on Avgas.

The thought occurs to me that had BRM ever found a way to get back to the 9,000rpm limit by 1958, the opposition would have been puffing hard to keep up with them. Had they discovered the cooling problem which was identified in 1960, would they have had the valve distortion problem? Or was it poor head-design problem?

Another "What if"?

The original design was labelled as relatively simple, but I'm not sure a 4 cylinder engine revving at 9,000rpm wasn't over-ambitious for those days. The 4 cylinder Vanwall had a limit of 7,400rpm on alcohol fuel. Both were subject to bad vibration problems, but Vanwall did a much better job at managing theirs.

Felix talks of being mystified by Peter Berthon's design decisions, and I think the same could be said of Tressillian's approach to the engine. It all looks like the P15 again, without the noise (PR and engine).

How does the historian capture the bad management factor? It is self-evident looking at the records, but how do you convey a sense of it?

A walk around the paddock in those days could capture some of the sense. So here is one.

Practice at Goodwood in 1957 (groan,groan). Mid-session, the cars are in the pits needing attention to the brakes. Salvadori, no.1 driver, is amusing himself driving a Cooper. Work is finished, with chaps in tweed coats in close attendance. One of chaps in a tweed coat fastens the bonnet clips (English car). Chief mechanic observes. Remember, in '56, a bonnet came off in testing and nearly collected Hawthorn's head.

Mays then inquires about Salvadori's whereabouts. "On the track," is the reply, "In a Cooper."

Mays, with a certain amount of huffiness, "Then call him in."

Everything I'd read about BRM up to then fell into place.

Another part of that history that is now hard to relate to is the nationalism that was part of the sport for that period in the '50's. We fans were just longing to see the green cars beat the red. The roar that went up when Hawthorn in the BRM pulled out to rocket past Fangio at the International Trophy Meeting could be heard on the other side of the Silverstone circuit.

Equally, Italians wanted to see their beloved red rule the day, and they did not give up easily. It was just a different dimension to the racing of that time, and it drove the chaps in tweed coats as well as the autocratic Tony Vandervell.