GTR2 GET REAL PHYSICS MOD 1.4

SUMMARY OF CHANGES


AERODYNAMICS

Big changes to how the splitter works. I have obtained new reliable information that confirms my suspicion I had all along that none of the cars simulated in GTR2 had different settings available to splitter. In other words - no adjustability on splitter at all, few cars used different size though (TVR) or different design (Force One Viper and 2004 BMS Ferrari 550).

Because of that I had to revisit this aspect of the mod and make appropriate adjustments since there was too much splitter downforce on many cars as a result as well as effect of diveplanes which was previously added on top but is already taken into account by default apparently. You can read more about this in the provided documentation. Cars which also had diveplanes will still have the option to change "splitter" setting to 2 and therefore increase front end downforce.
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CAR SPECIFIC CHANGES

Viper GTS-R

- Zwaans Racing and Roos Optima Vipers now use default splitter downforce.

- Belmondo Vipers used diveplanes IRL in Spa race and will now have them included in splitter setting.

- Force One Viper used a more sophisticated version of the splitter with endplates therefore increasing its base downforce. Force One Viper now also takes into account for diveplanes which were used on some tracks IRL so the total front end downforce is significantly increased.

- Megadrive and Scuderia Veregra Vipers remain the most basic version with the least front end downforce since they didn't have any diveplanes. Consequentially they are also the fastest in the straight line of the regular Vipers. Now use default downforce data corresponding to setting 1.

Due to all of the above regular Vipers now again will use original spec engine of 636hp and not 620hp (this was probably later spec car with smaller air restrictors). That way lap times again became spot on.


BMS Ferrari 550 - Previously both cars used the same splitter data. Now there are significant differences.

2003 spec - now use default splitter downforce data

2004 spec - significantly more downforce compared to previous version while at the same time having less drag due to its new design with endplates.

New splitter enables to take full advantage of a 2004 spec rear wing now resulting in 24% increase in overall downforce compared to 2003 car while having slightly less overall drag. This corresponds with comments made by Fabrizio Gollin at Spa 2004 who said that new spec car had more downforce.

Thanks do these aerodynamic improvements car will match lap times much easier than before and be a better match for the Saleen and Maserati in the corners.


JMB/Wieth Ferrari 550 - updated splitter downforce/drag. JMB Ferrari engine spec changed, lower maximum torque but more power after the peak RPM.


FERRARI 575 GTC - now uses 2 different engine specifications.

- 2003 model JMB car and 2004 GPC cars will use factory Ferrari engine with 605hp/730nm as claimed by Ferrari website.

- 2004 JMB cars used more developed version of the same engine as stated by Karl Wendlinger at Hockeheim 2004 and will therefore revert back to original spec engine with 612hp/735nm.


Lister Storm

Slightly reduced body drag/lift and moved center of pressure back to default value due to fixed splitter. New aero balance means that Lister needs very small wing angles (corresponds to photo evidence which shows little difference between high speed tracks/high downforce tracks) in order to stay stable which in turn makes it faster in a straight line and now matches speed traps perfectly. Overall it is even more of a beast of a car than it was before.

- increased mass for Creation Autosportiff Lister. This change was made based on a comments made by Jamie Campbell-Walter in 2004 Magny Cours where he said that Creation Lister chassis is an older and slightly heavier than factory Lister.

- due to this new info Creation Lister now reverts back to original engine spec of 589hp as this appears to be more realistic spec judging by the lap times.


Maserati MC12 - no longer uses tire width of 300/300 like it is claimed in brochure for later spec car but reverts back to original size of 310/345. This is based on video evidence where 2004 car had noticeably wider rear tires compared to the fronts.


Saleen S7-R - updated splitter downforce to GTR Evo setting 1 data resulting in less front end grip.

Body drag calculation is no longer based on public data for which exact Cd value is not known but is only an estimation (0,28-0,30). Rather I have reversed engineered this in order to find more accurate Cd value which is higher (0,334 to be exact) so now straight line speed of the Saleen perfectly matches speed trap data.

- changed mass back to 1250kg

- overall less downforce than before while having more drag (still significantly less than what was originally) but better overall balance due to less front end downforce. Just like the Lister, Saleen needs very small wing angle in order to achieve rear end stability.


Porsche 993 GT2 - new rear wing data; less efficient.


BMW Z3M - updated splitter downforce to match setting 1 data resulting in less front end grip. Increased body lift substantially. As a result there is much less downforce overall but more rear end stability due to new aero balance of the car.


Gillet Vertigo - new body aerodynamics with large increase in downforce.


Lotus Elise - updated splitter downforce to match setting 1 data resulting in less front end grip. As a result car is having more rear end stability especially at minimum wing setting.

Mosler MT900R - updated splitter downforce to GTR Evo values resulting in more front end grip.

There is now significant difference between the two versions. Rollcentre version has much more downforce overall thanks to its diveplanes which in turn allows for full range of wing settings to be utilized. Body lift decreased. As a result, aero efficency in significantly improved.


Porsche 996 GT3 Cup - new rear wing data


Seat Toledo - corrected tire size to a more realistic specification


Porsche GT3 RSR - updated splitter downforce. No longer uses excessive Simbin coefficients resulting in less front end downforce and more balanced car. Previously it had 15% more downforce than RS and the same drag, new tests have shown that 7% increase is more of a realistic number. Improvements to the engine power after peak power RPM.


TVR - updated splitter downforce/drag



TIRES


Pirelli tire grip coefficients are from now on based on 310/345 tire size. Since all the other cars have narrower tires than Maserati, as a consequence they will naturally have lower grip available to them as well. (about 1%) It turns out that all the brands share very similar grip coefficients when corrected for the tire size. This means less mechanical grip on Pirelli equipped 575s and Saleens for example.

All the cars in Spa 24H national classes which ran on same spec Dunlop tires (Morgan Aero8, Mosler MT900R and Gillet Vertigo) will have the same grip level (adjusted for their respective tire size) as Lotus Elise Yokohama tires. As a result tire grip on those cars is lower and they are outperformed by Pirelli Cup tires. However situation is reversed with the wet tires, here Dunlops provide for better grip.


TRACK SPECIFIC CHANGES


- Increased grip level on Barcelona, Enna Pergusa, Brno and Anderstorp tracks.

- Significantly decreased grip on 2003 version of Spa based on comments made by multiple drivers at 2004 race commenting about the new layout of the track.


Install this on a fresh installation of the game or over previous version.





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SUMMARY OF CHANGES


DRIVETRAIN LOSS

I have implemented new method of simulating drive train loss which is modeled inside the engine file itself rather than via HDC file clutch friction parameter. The reason for this is that the game engine does not automatically adjust provided friction value (calculated for maximum torque rpm) but instead it applies fixed value across the entire rev range which is incorrect and results at drivetrain loss which is not consistent across the entire rev range. There is minimum affect on car performance if you stay inside power band however but standing starts and low rpm/high gear acceleration is improved. Braking stability will also be slightly increased because of this change in more powerful cars.

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SUSPENSION

I have provided more accurate wheel mass data together with corresponding changes to their inertial values. Original cars had all the same unsprung mass (except Lotus) and too small inertial properties modeled and this is now fixed. Similarly spin inertia and wheel/spindle friction values have been updated to reflect these changes. They take into account new wheel masses and tire radius to calculate new values which were shared across the board previously. Of course this now also has small affect on a total drivetrain loss simulated per vehicle.


CAR SPECIFIC CHANGES


Viper GTS-R - tweaked body drag value based on a new radiator intake size reference area

Morgan Aero 8 - fixed slightly too low body drag

Porsche GT3 Cup - removed splitter as its already taken into account in body aero calculations (very understeery car but very stable and easy to drive). New body inertia values which were shared before with GT3-RS.

Gillet Vertigo, Viper Competition Coupe - updated splitter downforce/drag and body inertia values. Particularly Viper CC had its inertia set way too low compared to its mass.

Mosler MT900R - updated splitter downforce/drag.

TVR 400R - overhauled aerodynamics, the car has significantly more downforce now on high downforce setting, but with splitter on setting 1 there is almost no front end downforce and minimal drag. This was done based on a car speed at Lemans and photo evidence. More realistic engine with 400HP.

Creation Lister Storm - more realistic engine spec with 557HP

BMW Z3M - now uses road car engine with 325HP, mass increased to 1375kg with corresponding inertia changes. This has shown much more realistic lap times than before and is within 0,5 seconds from 2002 lap times at Spa.

Lotus Elise - updated body inertia values


Install this on a fresh installation of the game or over version 1.2
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Newest version features updated aerodynamics, new realistic engines and improvements to the tire model and AI.

Aerodynamics

All the cars got refinements to the aerodynamics, on some cars differences are noticeable, on others not. With the help of the chatGPT I have redeveloped certain aspects of the sim such as drag coefficients for radiators/brake ducts and tires which results in slightly more overall drag in most cars. Body downforce is also very slightly increased now taking into account lower rideheight and wider body relative to the road version of particular car. I have updated rear wing center of pressure values which differ from previous ones very slightly.

Tires

You will immediately feel that the front end of the car bites more now as front tires and now identical in performance to the rears. In original physics they were downgraded in order to get car stable because of the shortcomings in tire model. I was able to unlock full potential of the tire grip with this new latest update and now they will feel better than ever. AI tire model also got updated and is more realistic, which brings their performance closer to player car.

Engines

Previously I held belief that original data is authentic for engine performance. But tests using new update have revealed that some cars were consistently faster than they should be. It turns out that many engines were too powerful. Here is the full list of cars with new spec engines:

Viper GTS-R (Force One remains the same)
F550 JMB and Wieth
F575
Lamborghini
Saleen
F360 GT + GTC
Nissan
BMW Z3M
Gillet Vertigo (2 versions)
Lotus
996 GT3 Cup
Seat

for which exact specifications can be checked in the game.

Updated documentation

Install this on a fresh installation of the game!

Version 1.1 brings many improvements across the board. The most important beeing new tire model. Cars will have better front grip and therefore corner entry speed due to corrected front tires grip values which were not modelled properly in original game. Same sized tires will have identical grip coefficents on both axles. Tire sizes were corrected for certain cars. There is significantly better control of the car under coasting.

I have updated aerodynamic data for all cars also. For example many cars use fixed splitter now. Rear wing lift and drag curve have been updated since Simbin used incorrect linear model. What this means is that you will have more downforce available at lower settings and more drag at higher wing settings than before. Overall minimum and maximum downforce values stay roughly the same. Cars have different maximum settings available now due to their aero configuration.

I have implemented more accurate brakes behavior for carbon and iron brakes separately. Cars are more stable under braking due to new thermal model. Carbon brakes now run significantly hotter than before with a peak temperature in excess of 700 degrees C.

Implemented real gearboxes for selected cars which incorrectly shared their gear ratios with other cars.

Updated drivetrain loss simulation logic. As a result acceleration performance will be slightly better.

Updated AI physics model and made additional setups for them. Some tracks grip values were readjusted. No longer will AI have better grip on certain tracks. This was possible thanks to overall physics improvements.

Updated documentation

If you are using old version of my mod delete it first and then install this!