Cars going too fast ?

Posted by zifox 
Cars going too fast ?
Date: August 25, 2021 09:29PM
Posted by: zifox
I haven't played GP4 for many years, and just finished a whole season on GP3. While using quick races (3 laps, AI only) to check the mods I install, I get the impression that the cars are going too fast.

I've launched a race on Monza, with a default install (no mod, fresh install with 9.6 patch installed, using the nocd 1.02 executable), and the front runners are reaching 350kph in the straight, while achieving laptimes of 1:22.5. (at least two second quicker than the value recorded in the track info.

Does it seem ok to you ? Could anyone try it and see if they get the same result ?
Re: Cars going too fast ?
Date: August 25, 2021 10:47PM
Posted by: huskyman49
Maybe you should lower the values in the performance file... :-)
Re: Cars going too fast ?
Date: August 26, 2021 12:11AM
Posted by: TomMK
Seems reasonable - in 2001 the pole laptime was 1:22.2 and if you're doing a quick race then the cars will have low fuel and new tyres so it's reasonable they would be approaching the pole laptime.


Intel NUC 8i3, 8GB RAM, MS Sidewinder Wheel
Re: Cars going too fast ?
Date: August 26, 2021 09:25AM
Posted by: zifox
@huskyman49: No performance file is involved, I checked with a pristine install.

@TomNK: That's what I thought first, but then I realized that the AI cars seems to hit the rev limiter quite early, so I thought I had an issue, and the game wasn't able to adapt the gear ratios to the actual speed of the drivers.
The performance gap between GP3 and GP4 is quite large. :-O
Re: Cars going too fast ?
Date: August 28, 2021 11:04AM
Posted by: zifox
I did a few more checks, and saw indeed a difference between my installs.

Top speed at Imalo is indeed around 350kph on a stock install (so it is faster than GP3), but the cars struggle to reach it. The thing that seems weird at the very beginning with my modded install was that the AI cars were hitting the rev limiter on the tracks I tested: Nurb, Silverstone, Monza. (354kph on monza)
What was really stunning was that the cars didn't seems to be slowed down by the air: on monza after 340kmh the counter was still going up quite fast, until the rev limiter was reached.

My issue came from the .dat files of the tracks. I replaced the .dat with the original ones, and the issue disappeared. (while keeping the wad)

So my questions are : what is in the .dat files ? How can I see its contents ? Can I use a upgraded .wad and the original .dat ? It seems to works, but i'm wondering if i'm going to have issues with racing lines, or grip values.

Edited 2 time(s). Last edit at 08/28/2021 11:05AM by zifox.
Re: Cars going too fast ?
Date: August 29, 2021 12:17AM
Posted by: zifox
Ok so i did more tests and I see the issue. Some tracks, coming from trackpacks 2006 & 2007, seem to have issues with AI.

I've opened the dat files with GP4 builder, but I don't understand what I should look for to fix that kind of issue. How does the game read data and decides what speed will the AI do ?
Re: Cars going too fast ?
Date: August 29, 2021 12:37AM
Posted by: Prblanco
Magic data is what you're looking for.

Download CMagic and use it to extract magic data from the original tracks (which is stored in gp4.exe) then apply it to the modded tracks, and you should have the "unmodded" AI behaviour. This will work when the original and modded track layouts are the same.

If the track is not one of GP4's original season, you'll need to edit magic data in the .dat by yourself. There are AI grip and power modifiers for each difficulty level, modify these until you're happy. This can be done with both CMagic and GP4Builder.

Always backup your files before editing!

My unfinished tracks: []
Send bug reports and track editing questions to
Re: Cars going too fast ?
Date: August 29, 2021 08:59PM
Posted by: zifox
Thanks for your answer. I tried to see if i could *fix* the dat file, but I couldn't find one particular value to edit. At first I though the wind resistance was the key, but it had no effect.
I ended up injection the magic data from 2001 files into the 2006 ones, and it does the trick, so I'll leave it like this.
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