GP3 Advanced Physics Editor v1.02 - Help

Intellectual property of Aubrey Windle - May 26, 2001

Installation

Copy gp3phys.exe and the help file to your Grand Prix 3 Directory. It must be run from the same directory as your gp3.exe file. The other files in this archive are just for fun, and can be copied anywhere you wish.

Disclaimer

You do not have permission to include this program in any retail software without the author's prior consent.

The author will not be held accountable for any problems caused by this application. Back up your gp3.exe file before using this program!

Notes

I do not believe it is possible to cheat in hotlap leagues with this program. GPxPatch logs some of the physics data, and any data that isn't logged prevents replays from working properly in GP3. For instance, if you try to load a replay with different tire grip, you will see the car crash in the replay. Please contact me if you find a way to cheat with it.

I do not claim to know for certain what the values you can edit with this program actually represent. Lots of educated (more or less) guesswork was involved. I have put question marks after the ones that I'm most uncertain about, but maybe they should all have question marks. :) GP3 is the best modern F1 sim there is, but I wish it were a little more 'open' like say, F1CS2000, which keeps all of the physics data in simple text files. So instead of editing text files, I had to undertake this crazy project. :)

What's new

Version 1.02, May 26, 2001

Version 1.01, March 16, 2001

Chassis/General

Downforce Coefficient

The important thing to remember here, is that this value should not really impact your laptimes, except maybe on high downforce circuits like Hungaroring, or Monte Carlo. What this value does, is change how much wing you are running. It doesn't actually change the aerodynamic efficiency of the bodywork. I reccomend adjusting this after you have made all your other changes. It can be used to adjust the AI cars straight line speed, because it's much easier than changing all the AI car setups.

Downforce/Drag Ratio

With this you can adjust the amount of aerodynamic drag. If you lower the value, you will get more drag with the same amount of wing. Raising it will give you less drag. It affects the aerodynamic efficiency of the bodywork.

Mass

Fairly self-explanatory. More mass has a negative effect on every aspect of the car's performance.

X/Y/Z-Axis Rotational Inertia

This is a little tricky to explain. Basically, it's how much the chassis tends to maintain it's current rate of rotation. Increasing X and Z will make the car more sensitive to bumps and curbs. Increasing Y will make the car more stable but slower, your reaction time will not need to be as quick to catch a slide. There's no easy way to estimate a car's rotational inertia. The larger a vehicle's engine, gearbox, and fuel cell are, the more inertia it will have. I reccomend imagining the chassis as a uniformly dense "slab". That keeps things nice and simple, and you can use this equation to calculate rotational inertia for a slab:

Inertia = Mass * (a^2 + b^2) / 12
where a and b are length and width perpendicular to the axis of rotation.

I think GP3's default values are pretty close to the results you should get using this equation.

These only affect the human driver, and they will affect your laptimes.

Front/Rear Track

Silly me for thinking this represented the car's height. :) It's actually the track, or width between the insides of the wheels. Wider track means less weight transfer when cornering, and you have to be more careful not to run out of track.

Wheelbase

This is the length between front and rear axle. Longer wheelbase means more stable, less responsive handling, and less weight transfer when accellerating or braking. Formula 1 regulations don't specify wheelbase, so every car is different.

CoG Height

Center of gravity height. This affects how much weight transfer takes place during braking/cornering/accelleration. Lower means less weight transfer.

Braking Force

Self-Explanatory. See the included .g3p files to get some idea of how to use this.

Human Mechanical Grip

This is sort of like changing the car's weight, but not it's mass. Sounds weird, but I'm pretty sure that's what it does. This is not reccomended anymore, since you can now edit the tire grip. If you need to make the AI cars more competitive you can use something like GP3Edit to increase "driver performance".

Weight Distribution

This is how much of the car's weight is on the front wheels compared to the rear, so now you can simulate a front-engined car or whatever.

Engine/Drivetrain

Human Race/Qualy Power

There is some cause for confusion here. This is not your car's actual power, but only the number that gets saved to the gp3.exe. The numbers that you use for AI power in GP3Edit or GP3Master should be comparable to this number. The actual power for both human and AI depends on what you have the rev limit set to. See below for further explaination. High values can cause nasty problems with something like a slipping clutch that I don't have a fix for yet.

Upshift "Penalty"

This is how much the car slows down when you upshift. I've heard a modern F1 car can change gear in milliseconds, so maybe it should be much lower. Higher values actually seem to have a braking effect.

Flywheel Inertia

This affects how twitchy the engine is. A larger flywheel will make the engine rev more smoothly, and cause poor acceleration. Try 0.025 to make the engine note a little shaky as you go over curbs and bumps, which I think is a really cool and realistic effect. 8o)

Final Drive Ratio

Basically, this changes how long the gearing is. If the AI cars are hitting the rev limiter before they reach top speed, you can increase this value to make the gearing longer. You can also use the "Optimize" button, which will calculate it based on your max rpm.

Max RPM

This changes the rev lights as well as the rev-limiter. It does not, however, change the torque curve of the engine. Maximum torque is always at 10,000 RPM no matter what. In a way this is a good thing, since it allows us to simulate a more narrow power band by lowering the rev limit. One common complaint about GP3 is that the torque curve is just too fat, so you can cruise around in 6th gear and still do reasonable laptimes. Personally, I have yet to be convinced that this is not realistic, but at any rate, you will probably want a more narrow power band for older F1 cars, and turbocharged cars in particular.

Acutal Race/Qualy Power

This is how much power you really have. It takes your maximum rpm into consideration. Power = torque x rpm, so more RPM means more power. The AI cars will be affected in a similar way. I believe this figure is accurate to within 15 horsepower. You can enter a number into this box and it will calculate and update the "Human Power" box automatically.

Maximum Race/Qualy Torque

You can't edit this one, it's read only. Provided for merely your curiosity. It simply calculates torque based on power at 10,000 rpm's.

Tires

Front/Rear Lateral Grip

This is how much grip you have when cornering. Don't get too carried away editing the grip. A small change has a big effect. See the 1970 .g3p file for an example of this.

Front/Rear Longitudinal Grip

Braking/acceleration grip.

Front/Rear Slip angles

I believe this affects how the tire flexes when you drive. With larger values the car will give more warning before it starts to slide, but the handling will be more sloppy. I think the original setting is too small, but who knows.

All-wheel Easy Edit

If you don't feel like editing front/rear and lateral/longitudinal separately, you can enter grip and slip angle values here, and it will do the calculations for you.

Thanks to...

René "SDI" Smit for his help and for GPxPatch, etc. Steve Young and Sven Mitlehner for inspiration.