16 replies to this topic

[Pingguest]

The Group C cars created a huge amount of downforce. Until the fuel formula was abolished under pressure by Bernie Ecclestone most of the downforce was created by the ground effect underbodies. As we know ground effect underbodies were banned in Formula 1 because of the high cornering speeds and the phenomenon called porpoising, which made teams use rigidly sprung suspension.

But ground effects were not banned in the Group C. As far as I know the porpoising was minimized only gradually and the downforce levels continued to rise. What I don't understand is, why the drivers didn't complain about the physical forces?

Could anyone help me with this one? Thanks!

By the way, does anyone has the full Group C regulations?

[fausto]

Very rough reply...yes, (some) Group C cars had Venturi shaped underbodies, but they had to comply to rules that mandated a reference plate behind the front axle and a maximum height of the Venturi tunnels.

There was a minimun ride height, that was controlled solidly than with F.1s.

I think also that, being the weight of this kind of cars (heavier than Formulas) could have been a factor...

[Formula Once]

Probably because at that time drivers did not complain that much anyway; Coulthard & Co were still in karts...

Seriously: the size and shape of Group C cars of course provided quite a few opportunities to create downforce, but in fact the sports prototypes of the early nineties had much more still. A car like the Toyota TS010 got close to the pace of F1 cars at the time and primarily the use of a sequential gearbox (instead of an F1-type semi-automatic box) kept them for going even quicker, some drivers saying that the time needed to shift down sequentially before the corner prevented them to brake even later. These drivers will also tell you that these cars (the Toyota and of course the 905) are among the best they ever drove.

[doc knutsen]

Originally posted by fausto
Very rough reply...yes, (some) Group C cars had Venturi shaped underbodies, but they had to comply to rules that mandated a reference plate behind the front axle and a maximum height of the Venturi tunnels.

There was a minimun ride height, that was controlled solidly than with F.1s.

I think also that, being the weight of this kind of cars (heavier than Formulas) could have been a factor...

Gr C came into being for 1982, being primarily a fuel consumption formula, in order to allow a great variety of engines to power the cars, ie supercharged, turbocharged or atmospheric, stock-block or purpose-built racing power unit....and it worked well, too. Maximum weight was set at 800kgs, with no fuel or driver on board.
As far as aero regulations go, the original specs called for a flat reference plate, measuring 100x80cms,starting behind the back of the front wheels. No other parts were allowed to project below this plane, apart from the wheels.
Maximum length of complete car including wings was 480cms, width 200cms, and height between 100 and 110cms.
No air boxes were allowed forward of, or above, the highest parts of the screen. There were measurements for windscreen, for doors and for internal cockpit width (130cms), and for side window sizes (40x25cms). The front overhang was to be no more than 20% of the wheelbase,and the difference between front and rear overhangs was not to exceed 15% of the wheelbase. Maximum wheel rim width was 16". Venturii were permitted aft of the reference plate, but skirts were banned. Finally, the fuel tank was to be contained within the wheelbase of the car and within 65cms of the longitudinal axis of the car, fuel tank capacity being 100 litres.

For 1983, the C Junior class was introduced, broadly similar to the C1 cars but with a total wight of 700kgs and a fuel capacity of 55 litres. Interestingly, C Junior regs demanded pedals to be mounted aft of the front wheel centres, while C1 regulations did not not, at that time. Other than that, the FIA kept mucking about with fuel allowances and capacities, right through the life of Gr C. For 1984, there were some radical new regulations being bandied about by M. Balestre, including allowing IMSA spec cars to compete with Gr C...but to Gr C fuel allowances.

For 1985, C Junior officially became C2, and their tank capacity was raised to 100 litres. All cars manufactured after Jan 1st had to have the pedals mounted behind the front wheel axis, also aluminium roll cages were banned in favour of steel. Fuel allocation for 1000km races in C1 was 510 litres (5.53 mpg), and for C2 330 litres.

1986 saw and increase in length of the front crushable zone from 30 to 50cms, and the allowed rate of refuelling was increased from 50 litres/min to 60.

For 1987, exotic fuel blends were banned (toluene was out)...leading to the mass destruction of Porsche pistons in the first hours of the race at La Sarthe.

For 1988, the size of the reference plate was increased to the width of the full chassis, and length of 90cms for C1, 80 cms for C2. The height of the rear venturi was set at a maximum of 280mm. Fuel was to be 98,7 RON, and C2 fuel allowance increased slightly to 363 litres.

In 1989, the weight was increased to 900kgs dry, and to 750kgs for C2, and all races were now to be run for a length of 480 kms, with the exception of Le Mans. A Grand Touring class was included, and a new class for atmo engines of 3.5 litres and 750 kg weight - in other words, contemporary F1 mechanical bits with all-enclosed bodywork - was also introduced. C2 was eliminated for 1990, heralding the demise of the Championship as very few of the privateer teams - for so long, the backbone of endurance racing - had the means to go down the two-seater F1 route.

[Pingguest]

Originally posted by fausto
Very rough reply...yes, (some) Group C cars had Venturi shaped underbodies, but they had to comply to rules that mandated a reference plate behind the front axle and a maximum height of the Venturi tunnels.

There was a minimun ride height, that was controlled solidly than with F.1s.

I think also that, being the weight of this kind of cars (heavier than Formulas) could have been a factor...

But what about the porpoising? Didn't the Group C cars had the to deal with that problem?

And how did the FIA police the ride height? There were no skid blocks at that time.

[Pingguest]

Doc knutsen, where did you find that precise information about the regulations?

[doc knutsen]

Originally posted by Pingguest
Doc knutsen, where did you find that precise information about the regulations?

Er...from being involved very closely at the time, and still remembering quite well what was, for me, one of the truly great eras of sportscar racing. I still have the FIA Yellow Books in the loft, but I believe the information is pretty much accurate.

[Ray Bell]

I don't think you mentioned the minimum weight for the cars built under the '62 regs...

As I'm looking closely at one of these cars, I'd like to know what that was, please.

[doc knutsen]

Originally posted by Ray Bell
I don't think you mentioned the minimum weight for the cars built under the '62 regs...

As I'm looking closely at one of these cars, I'd like to know what that was, please.

Even M. Balestre did not have sufficient imagination to work out Gr C weights in 1962 ;)

[Bill Becketts]

For 1987, exotic fuel blends were banned (toluene was out)...leading to the mass destruction of Porsche pistons in the first hours of the race at La Sarthe.

Doc. I was there and the story then was that the fault was due to the quality of the fuel supplied by the organisers. Please tell us more..

[Ray Bell]

Originally posted by doc knutsen
Even M. Balestre did not have sufficient imagination to work out Gr C weights in 1962

Please, humour me with the 1982 figure then...

[jeremy durward]

Originally posted by Pingguest


But what about the porpoising? Didn't the Group C cars had the to deal with that problem?

And how did the FIA police the ride height? There were no skid blocks at that time.

i have read a few stories of group c cars porpoising, notably the peugeot 905 and i also remember reading an article about alan jones i believe racing a porche 956/962 which after destroying one nose had to use one which promoted a lot of it.

[doc knutsen]

Originally posted by Ray Bell


Please, humour me with the 1982 figure then...

The Gr C weight when the rules first came out was 800kg dry, as I wrote in my previous posting. The 956 Porsches initially had trouble in getting the fuel consumption to match the fuel allowance, and in the first season the little Lancia barchettas were pretty competitive. However, once Mr Bosch got the Motronic sorted and the development in electronic management systems got into gear, the 956s were able to unleash their potential, despite the weight being upped to 850 kgs an later to 900kgs.

[Bonde]

Fredrik,

Was structure or systems added to the cars when the weight increased from 800 kg to 900 kg - or was everyone simply compelled to add ballast? An increase of 12,5% is a lot! And why the weight increases? To keep lap times in check? A heavier car isn't necessarily safer - all component loadings increase, both under normal operating conditions and in an accident. Seeing as how modern LMP cars are built (F1-style technology), they must surely carry a lot of ballast under the current rules! IMO not a good idea. Ballast just adds to crash energy.

Pingguest,

You might find some Group C downforce and G-figures here.

[doc knutsen]

Originally posted by Bonde
Fredrik,

Was structure or systems added to the cars when the weight increased from 800 kg to 900 kg - or was everyone simply compelled to add ballast? An increase of 12,5% is a lot! And why the weight increases? To keep lap times in check? A heavier car isn't necessarily safer - all component loadings increase, both under normal operating conditions and in an accident. Seeing as how modern LMP cars are built (F1-style technology), they must surely carry a lot of ballast under the current rules! IMO not a good idea. Ballast just adds to crash energy.

The chassis dimension requirement changes meant longer-wheelbase cars, adding a bit of weight in itself. (moving the pedals behind the wheel centre-line). Also, many parts needed beefing-up with the increase in downforce.
The early 956 Porsches were down towards 800kgs, but that was a SWB car with a sheet aluminium tub and an aluminium alloy roll-cage, later versions had to have more substantial steel cages. Also, things like brakes and wheel bearings grew with development. The Porsches, and many other cars, still had fairly heavy glass fibre bodywork, and customers built stiffer (honeycomb) tubs which were also heavier. I do not believe many folks were able to play the ballast-in-favourable-places game in those days, simply there were no budgets for exotic weight-saving measures. Most cars were, in fact, not down to the weight limit anyway.

Why the weight increases were introduced I simply do not know, although it was seen as a "safety measure" in certain quarters at the time, hopefully slowing the cars down. But of course, once the driver loses a heavy car, the ensuing accident is going to be a bigger one, with more kinetic energy to dispose of. For a good example of the levels of technology in the early Eighties, compare the Nimrod Aston Martin's steam-engine like suspension components to the lithe parts of the 956.

[doc knutsen]

Originally posted by Bill Becketts
For 1987, exotic fuel blends were banned (toluene was out)...leading to the mass destruction of Porsche pistons in the first hours of the race at La Sarthe.

Doc. I was there and the story then was that the fault was due to the quality of the fuel supplied by the organisers. Please tell us more..

Everybody who ran turbo engines mixed toluene into their fuel in those days...been there, missed out and burnt the pistons! The fuel supplied at Le Mans was thought to be sub-standard and the management systems had to allow for the difference in the fuel. The usual thing was to ****** the ignition and turn the boost down, but the Motronic 1.2 was not that sophisticated and running high boost with the "standard" fuel was brinkmanship in extremis.

[Charles E Taylor]

[B]Phyisical effects of ground effect Gp C cars


An interesting comparison is that of the 3.5ltr sports cars of 1992/93 compared with the 3.5ltr F1 cars of the same period.

The "Gp C" cars weight limit was 750kg, appx 50% more than a F1 car of the time. The engine power somewhat less, (100bhp perhaps)

If you can find the data take a look at the fastest laps in the Monza 1000km race of 1992 and the F1 GP of 1991.

You will be very surprised what less drag and more downforce can do.

Those cars were extremely quick.