There isn't a Mac version of GTP.
Mac users run GTP using PTA physics (exe).
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GTP to PTA conversion: GTP>N Mod Pack mod.rar
From the readme:
Installing GTP cars from the original GTP Mod with the .gtp or .gtn extention on the car file:
1) Copy the cars and paste them into the GTP\cars folder.
2) Rename the extention of the cars FROM .gtp or .gtn TO .pta
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This will visually give you the gtp cars, but you're not going to experience the dynamics of the GTP mod because you'll be using the PTA.exe.
To get better downforce characteristics you'll have to employ the owr07 tactics, higher grip values.
pta2modX:
The "pta2modX" is for a higher grip "pta.exe", for aero sportscar/prototype mods that were developed to use an altered exe physics model, but are now run with pta physics.
I adjusted the "grip level" to allow the pta model to be able to run the course similarly to the Redline gtp cars that use the modified exe. It can't make up for a lack of horsepower, so for a setup I used the pta six speed tranny ( a 5 speed is also available ). The "feel" of the "mod car" is partially dependent on the weight distribution of the car, the farther toward the rear, the more it will feel more like a mid-engine car. Because of the added grip, some weight must be moved rearward ( from a normal pta setup ) in order for the car to be free enough to go fast, but there are diminishing returns, so it's up to each individual to decide if speed or feel is more important, but tire heat is a limiting factor for too much forward weight. The laptimes are significantly slower than actual gtp laptimes, but are some seconds faster than what the normal pta cars are capable of.
The mods I thought could use this alternative : specifically GTP & AD67, and GrandAm cars if you know how to set up your install to add the series. It may work for OWR, but the owr tracks generally have much higher grip levels (1.5 to 2.x).
For a while I was adding this track.ini variaion to the tracks for which I was developing ai, but it takes a lot of time to do each series and for lack of feedback (and I suspect use) I decided to drop this series.
Here are the tracks that have this series:
I have more recently come up with a better way to get the pta.exe to more closely resemble the "illegal" mod exe's, specifically owr07.
It requires a lot more work and the track surfaces have to be modified via the ptf.
With the "just raise the asphalt and concrete grip levels" method, the grip feels more mechanical ("sticky asphalt") than aero. The laptimes also fall short, and it takes really off the wall rear weight setups to even achieve those times.
That got me to thinking about using paint (in a major way) as the track surface. I could increase the grip value and still have some slipper-i-ness. OWR (operating with the pta exe) requires the track to be a combination of surfaces, each with their own grip value, and each surface placed to produce a specific grip level for specific track conditions.
Asphalt: Generally the lowest surface-type grip value, 1.50. Use on the straights.
Concrete: Used for braking zones, high speed kinks, and VERY slow corners, 1.7 - 1.8.
Paint: Used for faster corners since it will allow the car to drift, 1.9 - 2.1.
It's certainly not like a hacked exe,i.e. it's not exactly like having front wings (or their adjustability), but for a sim based on a stockcar with virtually no front aero downforce, IMHO, it's immensely better than just high grip asphalt as a substitute.
Try the results: Long Beach 2010 Owr
[You don't need owr07 installed, any pta mod will do. You can just imagine your driving an open wheeler.]
