As far as i remember, LFS S2V is the last version where you could choose the psi, turbo, displacement and tyre/rim dimensions for the XRT. No need to use the old Q version. I don't know though if you can still unlock it. pm me if you don't know where to get them.
Thats because of your weird setup. Where did you get it? Locked diff on front :nut: -> the car understeers a lot, impaired by too much camber. Tyre pressure is too low, i think, makes the car feel loose and react slow.
same here: way too low tyre pressure plus too soft springs
<= locked diff, low tyre pressure, stiff anti roll bar on the rear.
Use the race_s setups, they are pretty good at the beginning.