Thanks for your comment and suggestions. As I say, we only work on stock, grA and DTM versions. I just upgrade tyres to Kunos street on the drift version. I'm not an expert in the art of drifting so it's hard for me to have the good feeling with it. I can ask to a real drift driver what needs to be improved the drift version.
This is my first experience in physics modding, so I have to learn more.
Fair enough. I could say a lot, but you will improve with time anyway. Just keep studying.
If I had suggestions, it would be to set the STEER_ASSIST to 1, or the forces will not feel right. If the cars retain the original PS I would even use the same STRENGTH for all.
About driftcar setup, it's no hard rule but often you will want to run your front axle stiffer than the rear, by some .3 - .5hz for example. Possible to go even stiffer. The car needs to understeer to be balanced in a drift. Some even remove the rear rollbar entirely. The trend is also for quite soft suspensions, around the 2hz mark or below is what I like personally. Rear traction especially is key.
If you want to improve the steering geometry, look around about lengthened lower control arms, lengthened steering arms, angle kits, steering knuckle grinding. The RS500 is, presumably, MacPherson front, so it wouldn't be that complicated to lengthen the LCA and steering arm, install a steering rack spacer to said steering arm and grind down the steering knuckle stops for more clearance. For example a +20mm longer LCA will result in a +40mm wider track, more or less. It will change the camber and steering geometry in a strut car, but it will allow you to run a longer steering arm as well and potentially gain steering lock. Grinding the stops will simply allow for more steering. Not sure if it's like this on an RS500 but it's like that on Silvias.
If you want a quick n easy way to lengthen suspension arms to a reasonable degree of precision, without using any complicated maths or CAD software or anything, use Geogebra's 2d grapher and input the susp coordinates in. Learn to use the "line with a given length" feature or whatever it is called and figure out the rest. It won't be 100% precise but within manufacture tolerances I say.