Ciao Paolo!
I wonder if one of my spyware programs is blocking access to the GTL multiplayer site? I'll have to do some digging.
I gave up on the mother because it is such a long track and I couldn't stay on it with the GT40. But I reinstalled it last night, so I'll give it another go now that I have the GT40 handling well.
How well? I just did a GT40 only race at professional level at Le Mans and got a 4:49.6. The next fastest was 4.52! So maybe it doesn't matter if I can't bridge the gap to the Panteras and 911s at this level.
I agree the GT40 is a pig in GTL, but I'll give you some hints to getting it handling reasonably well (without giving away too many of my secrets).
Drop the tyre pressures well below the default. The front and rear camber should also be less than you expect for a car with racing tyres. Experiment in free practice until you get the temp change across the tyre fairly even with a slight increase on the inside edge of the tyre. Make sure you warm up the tyres (and brakes) properly before analysing the data in the garage.
Drop your differential percentages to 20% or less.
Drop your spring rates and sway bars to the lowest setting available. Set Bump to 2 and rebound to 1.
Set your gearing for the track. Use 20% front toe out and 10% rear toe in.
Play around with your braking bias. Move it to the front far enough so you don't get the back coming around as you trail-brake into the corner. I like about 98% line pressure so I can scrub off a lot of speed when going fast, and ease up on the brake as you approach lockup as you slow down.
I set the steering to 12* lock so it's not too sensitive to small inputs, and put castor above 4*.
These basics will give you a car that turns in ok but will oversteer on exit unless you are very smooth on the throttle (I have my controller set to 100% sensitive with 10% deadzone on the pedals, so it's easy to get the right acceleration and braking). You can add a little front ARB to help with the oversteer if you want, but this will be at the expense of turn-in.
I've tried a lot of combinations to get my fast times around Le Mans, and lots of them will be almost exactly as fast, but far less driveable than a setup like the above. A fast car that you can't keep on the track might get you a good lap or 2, but you won't win many races!
Let me know how you get on. If you do get your GT40 to handle well at the mother let me know your PB. I'll give it a go myself, too.
I'll also try and get my multiplayer working...