Physics ReadMe for WSC70

WSC70 is a set of racing cars from the late 60s which raced in the World Sportscar Championship of 1970. We have most of the important cars and a few others as well.

We have done what we could, using the information we had at hand and working around some limitations in controller hardware and rFactor itself, to model these cars in a realistic and individual fashion while trying to ensure they are fun to drive for the driving sim enthusiast. The cars are not pedantically accurate replicas of the real thing as this is not practical, but we used real values for the car's attributes where we could. Engine power curves are taken from published curves where we could get them, so in some cases you will experience torque curves with humps and valleys over the rev range. Likewise, gear ratios are from the makers' data where available and we used drawings, models and photos as input for the suspension layouts.

The cars are configured for LeMans by default, so they are geared for top speed. Alternative FD ratios are available for twisty tracks. Tyres are cold to start with, as there were no tyre-warmers in 1970. They should be up to temperature in a few laps. Short twisty circuits may require the tyres to be changed from Softs to Hards.

Assists are enabled so that inexperienced drivers might find the cars a little easier to drive to start with. However to get the whole experience of the period, the cars should be driven with all assists off and manual shifting.

Our intention from the start was to let the personality of each car show through. The chassis, body and drivetrain all have a part to play in this approach to reality. It means that the cars are different in speed, grip and feel from make to make and from model to model and we have not tried to tune this out. So the Real fast cars remain faster and the slower ones never catch up unless the faster car breaks down - which they do from time to time. It's more fun this way and provides a variety of driving experiences. The result is interesting competition between cars of different classes. 

In Real Life, not all these cars were reliable enough to last the 24 hours of LeMans. Our cars mirror the actual experience, so if you want to race a real 24 hour race, make sure you choose a car which has a good chance of lasting the distance.

Some of the cars of this era were a challenge to the chassis and tyre technology of the day. The cars at the top level deliver power and speed not seen before and their performance challenged the ability of the drivers to deliver their best. The fastest of these cars are not easy to drive, but you had to be at the top of your game to drive them in Real Life. If you find the faster cars to be a challenge, try some of the smaller-capacity class cars to get your hand in.

1970 was the second-last year of the 5-litre Sports Cars class in the WSC, a class for which 25 examples had to be built. Famously, both Porsche and Ferrari made 25 and more copies of their new cars, the 917 and 512S. The other members of that class were the Lola T70 Mk3B and the Ford GT40 Mk1, both designs being from earlier years and somewhat out of the front rank on power and/or weight. 

Prototypes were limited to three litres in the WSC, and we have cars from Alfa Romeo, Ferrari, Healey, Matra and a variety of Porsches. These cars were fast but brittle, and the 3-litre cars were not up with the big sports cars in 1970. They became competitive in 1971 and they came into their own in 1972.

Contenders for class wins include the Porsche 906 "Carrera 6" and the 910 prototype which was derived from it, plus the Chevron B16. The GT 2000 class has the Porsche 911 in 2 litre and 2.2 litre form and the 914/6-GT. The GT 5000 class has Corvette L-88s, a Ferrari 365 GTB/4 Competizione and two Group 2 Mustang notch-backs.

By 1970 the suspension design for prototypes and sports/racing cars had settled into the layout shown by Colin Chapman in the Lotus 18 and refined in the 24 and 25. Double wishbones of unequal length at the front, with a combination of transverse links and trailing arms at the rear which were effectively another set of double wishbones. Coil-over dampers - double-acting single speed - were found outboard front and rear, along with disk brakes. So there were a lot of similarities between cars. Each suspension file has been built to reflect the actual car as we understood them. The road-based cars retain their original suspension and brakes layout so there is quite a lot of variety.


These notes are about the individual cars and their physics.

Porsche sports-racing cars -

It is apparent from the amount of information available that Porsche's approach to engineering their racing cars was orderly and quite well documented. They took few big leaps into the unknown and each new car was derived from the successful cars of the recent past. When they built 25 of the 4.5L 917s and announced they were going after line-honours at LeMans, the car was a beefed up version of their earlier long-tail 907 and 908 design. They already knew that the streamlined long tail produced lift, but they missed out on how much lift would result at the extreme high speed of the new car. In 1969 form, the 917LH was lethal. The actual story of how the car was worked into a practical winner is quite interesting. The 917 was always a challenge to drive, and proved slower than the more nimble 908-03 over twisty circuits.

Porsche sports racing cars of the later 60s all have their genesis in the 904 GTS. This car was conceived as a car to be sold to customers and it had a steel chassis and fibreglass bodywork so it could be easily repaired. The 904 is not in our car-set as it was too early, but it set the basic dimensions for the future and the wheelbase of 2.3 metres was used by Porsches sports-racing cars well into the '70s. We do have the 906 and the suspension of the 904 was reused for that car, the very successful customer-car of 1966. The 910 was derived as a prototype from the 906, with smaller wheels, wider tyres, a bit less weight and a bit less drag. Both cars are relatively conventional prototype/sports-racing cars of their era with unequal length double wishbones front and rear. 

Porsche believed in allowing racing cars cars to stick to the road by enabling reasonable wheel movement. They did this by making suspensions which were somewhat softer than some of their competition - a leaf out of Lotus' book. So these cars are not rock-hard to ride in and they respond to subtle steering and throttle input. We have 906/6 and 910/6 cars, plus the 908-02 in standard and Flunder bodywork, the 908-02 Flunder Langheck which came 3rd at LeMans and some of the lightweight 908-033 spyders in this mod. The 908-03 was built to run the daytime only events on twisty tracks for which the 917 was less suitable, like the Targa Florio and Nurburgring. To cut weight it had no front lighting equipment! Even so, it was limited to the best of the flat-6 engines built for the 908s and about 360hp. Porsche was limited at that time to two valves per cylinder by their agreement with VW about support for air cooling. There was not enough room in the cylinder heads for four-valves per cylinder and air-cooling, and eventually someone gave in, but not in 1970!

The 917 was a challenge. It encompassed some interesting decisions in body design which were eventually addressed to some extent by the 917K. The wheelbase was a bit short and the power tended to overrun the chassis. There was also some adventurous suspension geometry in the earlier cars and stability was questionable for several versions just before our period. Even at it's best, it was very powerful, heavy to drive and had limited handling on twisty circuits. Have fun!

Ferrari sports-racing cars -

There are a few Ferraris, as there should be for endurance racing in the 60s and early 70s.

The 5-litre 512S is the main event for the year. Competitive with and arguably slightly faster that the Porsche 917, the 512S had veriable results in Real Life due to poor preparation and sloppy team management. RF cannot respond to much of that so the 512 will be faster at times which seems surprising. C'è la vita!

The 512 comes in Short and Long Tail version in a variety of body shapes, and also Berlinetta and Spyder. Performance varies as they all have different aero characteristics!

The appearance of the 312P in 1969 presaged a new line in Ferrari history, but in this case it was underveloped and suffered from poor press about it's abilities and from lack of focus on actual performance. The lovely car of 1969 and 1970 disappeared in later years, after a period of promises unfulfilled. 

Lola T70 -

The Sports 5000 class is rounded out with the Lola T70 Mk3B. This was the re-engineered version of the T70 coupe, with 5-litre 465hp Chevy V8. Never terribly reliable, the T70 did not repeat the win it enjoyed at Daytona in 1969 and was now towards the end of it's racing life. As much a product of the British Cottage Racing Industry as anything else, it suffered from lack of big-team involvement and the poor endurance capability of the Chevy small-block V8.

Ford GT40

Conceived in 1964, the GT40 Mk1 was largely obsolete by 1970. Entertaining in the hands of privateers, it was a journeyman endurance racing car from a few years ago. Other car's weights had gone down and power had gone up since then, so the GT40 was at the back of the 5 litre Sports pack. Easy to drive for long periods though!


Alfa Romeo -

We have the 3-litre V8 version of the T33/3 spyder, in long-tail form. It has a typically peaky engine and is reasonably light, but not terribly reliable in 1970. The six-speed gearbox is a standout in this class.

Matra - 

Matra were "quite French" during the period of our cars. Bernard Boyer architected a series of automotive designs which pushed the frontier of auto-racing design - not always in the right direction, but he was imaginative. Some of the modifications seemed to be chosen so that they were different from what other makers had done. The MS650 "Pedalo" is just one example.

We have the MS650 with MS12 V12 3-litre engine and its fabulous exhaust note. The MS12 was a peaky engine with a big hole part-way up the torque curve. The upper three gear ratios are somewhat bunched together to avoid falling into it.

The MS650 comes in Standard, Front Airfoil and "LQ" (Pedalo) form - each with their own characteristics.

Healey -

The Healey XR37 was the Last Hurrah of a famous British designer at the end of his powers. The XR37, as raced, was a derivative of a rear-engined coupe with a Climax engine. The car was adapted to accomodate a Repco-Brabham 3 litre V8 in detuned form and the roof taken off. It reached the 23rd hour at LeMans, before expiring. It never raced again and was subsequently sold off after the race damage was repaired. The car is currently in Australia, largely intact.

Chevron -

The Chevron B16 was a more modern car than the Porsche 906 and 910 in the 2-litre class. Lighter and with more power, the B16-Cosworth was faster but less reliable. The BMW - engined version was an attempt at more reliability, while the version with the Wankel rotary from the Mazda R-100 was an interesting experiment.

Porsche 911 and 914/6

All these cars have versions of the 6-cylinder boxer engine originally released in the first 911. The 2 litre 911 has 200 hp and shares this engine with the 914 where it develops 210 hp, plus there are 210 hp and 230 hp versions of the 2.2 litre engine in 911s. Porsche engine files are based on published data, mostly from Paul Frere's book "The Racing Porsches".

The A- and B-Series 911 has McPherson strut front suspension and semi-trailing arms at the rear and the 914 has a variant of the same layout. The rF version of the chassis for these cars has an emulation of the strut suspension and a rearrangement of rF-style double-wishbones at the rear to function as the semi-trailing arms. The result is interesting as the overhanging mass of the engine in the 911 translates into a car which has more oversteer than the mid-engined 914, and has slightly slower on-track responses due to the relatively higher inertias. As you would expect, the characteristic strong oversteer is manageable for a skilled driver but one must pay attention. The result is that the slightly lighter and more agile 914 will mix it with the more powerful mid-range 911s.

Corvette L-88

This is the C3 version of the L88, with 427 cid engine and 550 hp. One of the heavier cars with lots of torque, so it needs a gentle foot in corners. Classic Corvette suspension underneath.

Ferrari 365 GTB/4 Competitione -

Group 2 version of the classic GTB/4. Front/mid-engined, gearbox in a unit with the differential, independent suspension on all wheels, with big disks all round. Classic 60s GT car. A lovely car to drive. I hope you enjoy it like we do.

Shelby Mustang Group 2 -

With the GT-350 homologated as a 2-seat sports car, the notchback was put up in Group 2 as a four seater, otherwise it was similar underneath. An interesting car to go racing amongst the 911s, the rear drum brakes are a weak point.

Drivetrains -

We found a comprehensive set of actual ratios for the Porsches, as well as for the Hewland and ZF boxes in a number of cars and for the American transmissions so there are plenty of options avaliable. The default gearing for each car is set for LeMans where the ratios were published for that track, so they are quite long-legged in standard form. For tighter tracks, the final drive ratio may be increased in the garage, which will increase acceleration at lower speeds at the expense of top speed.

Aerodynamics -

In Real Life some of these cars developed lift and some developed downforce. The science of aerodynamics as applied to racing cars was in it's infancy and we can see a lot of guessing and copying what the best were doing. Porsche seemed to know most about what they were doing and had been runnung wind tunnel tests for some time in their pursuit of low drag. However the results suffered from lack of wind tunnels with moving road surfaces, so the correlation between wind-tunnels and track testing was patchy and contradictory. There are also issues with the way tyres in rF deal with changes in vertical load - for my tyres anyway. So there are some compromises as well.

The regulations, as expressed in Appendix J for 1969 from the FIA, stipulated that cars had to be able to be driven over a box 100mm high with driver and fuel on board. Hence all these cars cannot be lowered beyond 100mm. Altough some of the later Porsche 908s had small splitters, the relatively high clearance would have limited their effectiveness. Accordingly, the effect of pitch on downforce was limited. As well, these cars had no diffusers so there is no ground effect either.


In building the physics I had inspiration from many sources and from other mod builders, including but not limited to ISI staff, and the members of CSGT and of Trellet.mod. I built the files using spreadsheets based on the principles described in my threads on physics in RSC. I used TP's Suspension Editor to look at the suspensions and Kangaloosh's CarFactory to analyse suspensions and parts of the tyres. Then I used RealFeel to drive them and MoTec to iron out some of the on-track issues. Thanks to all these people.

If you want to modify these files or use these files on any other cars or platforms then you need my permission. If you are interested in joint collaboration then please make contact via RSC or RFC where I have the same moniker.

We had fun building and testing these cars and it taught me some interesting things about rF. I hope you enjoy driving them.

Bristow - June 2009