[Physics Update] P1, P2 & Daytona Prototype - 27/01/2022

Note: the #1 old setups will not work with any updated cars. Trying to use these setups will result in a very poor handling car. They must be deleted!

First, some background..

The Le Mans Prototype classes can trace their roots back to the early 90s WSC category, them selves grew out of the decline of the Group C & GTP series. The idea was to reign in the massive downforce produced by the aforementioned classes as well as reduce running and development costs. The LMP classes went through several variations, before arriving in 2004 at the faster P1, and more restricted P2s.

P1s have a minimum weight of 833kg for none hybrid, 878kg for hybrid. Fuel tank sizes are different depending on fuel type, hybrid or not, and engine displacement is unlimited except for those with a hybrid drive which were limited to 5.5litres. The series organisers retained the right to alter fuel tank size and minimum weight in order to balance the performance of different car configurations.

P2 takes the same ideas as P1 but with reduced performance. Engine capacity is capped at 4.2l and minimum weight is 950kg. Bodywork must cover all wheels and cars can be both open topped or with roof. From 2011 the series mandated that engines used in this class should be production based.

We also have the Daytona Prototype Corvette in our midst. These raced exclusively stateside and were the brainchild of the Grand American Road Racing Association. Their series until 2002 used P1 and P2 regulations, but with spiralling costs and reduced grid sizes they decided to take action. The Daytona Prototype is required to use a steel spaceframe chassis, unlike the carbon tubbed P1 & P2. It must also use a series approved production engine. Carbon brakes are not allowed, diffusers are prohibited and the roof dimensions are stipulated by the regulations. Hence some unpleasing looking cars of this era. Although I always found the Corvette the prettiest of the lot.
During the amalgamation of the two American endurance racing series in 2015/16 the Daytona Prototypes were permitted to make some changes, such as increasing their power, adding traction control, reducing weight and adding an underbody diffuser. All this in aid of allowing to compete with the P2s they were now racing against.

So what's new?

This update was (another) completely clean sheet. What's old was forgotten and started afresh. Thankfully we already had updated the engine files recently by adding engine maps and modes to them, so they were a useful base. We also had a nice selection of endurance tyres with the RSR GTE which served as a good base to develop from.
The first step is to define the dimensions of the vehicle, where the wheels sit, centre points of the wings, where the engine sits in the chassis etc. Then the weights of components are defined. Everything from brake calipers to the extinguisher and wishbone weights are all defined and help to build up the big picture of a car's character. From those first two steps we can then start to calculate inertias of parts, unsprung weight, centres of gravity and so on.
Then we get to the really tricky stuff. The tyres have to be defined not only in dimension but every part of their character from how much they grow due to centrifugal force at speed to how much grip they give up at a given slip angle and load. This bit is very tricky, takes a lot of time and a lot of extrapolation of data as unfortunately tyre data is rather a secretive affair.
Brake behaviour is then calculated, as well as engine torque curves, gear ratios, suspension layout, spring rates, damper rates, wing positions, downforce and how it reacts to different conditions. There are literally 1000s of parameters to go through.

Only then are you ready to hit the track. Only to find it needs 100s more hours spending to perfect it.

The result is..

Audi R18 - P1

Ridiculous amounts of torque and quite a lot of downforce. Engine runs out of steam way before the redline so make sure you short shift. Aero balance is extremely forward so it changes direction like a single seater at high speed.



DMD P20 - P1

There's a stonking great 6.0l V12 in the back of this. Plenty of torque and a beautiful sound. It's drawback is the higher centre of gravity due to the V12s layout, as well as a more rearward weight distribution which can make the rear tyres suffer on long runs.



Mistral M530 - P1

A generic P1 based on the small (3.4l) V8 powered cars of the era. Is fairly close to the R18 in terms of behaviour but lacks the huge torque of the diesel Audi.



Radical SR9 - P2

I was fortunate enough to be able to ask a former colleague who raced one of these at Le Mans for the lowdown on it's behaviour and I've managed to recreate the nuances he described. It comes in two engine configurations - the 4-cylinder AER turbo, and a Judd V8. Both are capable of the same lap times, but the AER has more torque while the Judd is a revver. This is another car with a very forward aero balance, so don't chicken lift in those fast turns else you'll be going backwards fast.



DMD P21 - P2

Fitted with a nice raspy turbocharged V6, based on the Honda unit used in several cars during this era. It's a little bit heaver at the back end due to the extra weight of the turbo chargers, intercooler and other turbo paraphernalia. Is a little bit more draggy too due to the air being worked harder by the extra cooling requirements.



Mistral M531 - P2

Same engine as the Judd powered Radical, with a slightly different chassis philosophy. It has a bit more power than the Radical as it lacks the downforce but makes up for it with grunt.



Chevrolet Daytona Prototype - P2

Behaves quite differently to any of the other cars mentioned here, and so it should. Compared to the other P2s it's classified with, it has more power but less downforce. As already mentioned it uses cast iron brake discs and not carbon fibre like the rest. Take care to remind yourself of all that if you swap from the other cars in to this one. I find this car particularly rewarding to drive. Maybe because it's not so good at the turns and the V8 sound is quite brash. Maybe it's a hooligans car, and I like it.

 

Typo, meant traction control.

 

- Reduced tyre wear rate by 10%

- Adjusted slip and flex behaviour to give a stiffer feeling tyre

- Increased fidelity and range of brake bias setting

- Setup tweaks to work with tyre changes

 

Sounds like you need to adjust camber and pressures.

 

Did you turn traction control off?