Which values affect braking/down-shift instability, especially cars with no downforce?

[Pizzicato1985]

I've been trying to get a few cars stable, the RX500 and the real challenge, the Aston DBS3 '53. The RX500 I can run laps with by trail-braking as this seems to calm the car down, but its not helping at all with the Aston. They drive fine in a straight line. Hell they even corner fine, but as soon as I tap the brakes and down-shift they violently jerk from side to side. I've spent almost my entire day off trying weird settings like really high toe values, running tow-out front and back + vice versa, every combo of camber angle possible. Really stiff damping all the way around, really loose damping, combo's of the two... I've added weight and changed the weight distro and then gone back through and tried all these things again, all to no avail. I've tried high anti-roll bars, low, high in the front/low in the back, vice versa, middling values. I'm out of variables to play with.

Braking sensitivity on the LSD helps when its a really minor problem, but for cars like the DB3S with the Supercharger added it doesn't help at all, at least not in any configuration of LSD/Suspension/wight distro/brake balance I've tried. I've spent more time trying to tune this Aston today than I've spent actually playing the game in the last week, and Im not seeing any progress. What am I missing?

Any suggestions would be greatly appreciated. I'm not asking for the top tuners to tell me their secrets, I just want a nudge in the right direction so I feel like I'm actually getting somewhere with this recurring problem that's been plaguing my setups for months, though it's really coming to a head with the DB3S in particular.

 

[B80]

I've been trying to get a few cars stable, the RX500 and the real challenge, the Aston DBS3 '53. The RX500 I can run laps with by trail-braking as this seems to calm the car down, but its not helping at all with the Aston. They drive fine in a straight line. Hell they even corner fine, but as soon as I tap the brakes and down-shift they violently jerk from side to side. I've spent almost my entire day off trying weird settings like really high toe values, running tow-out front and back + vice versa, every combo of camber angle possible. Really stiff damping all the way around, really loose damping, combo's of the two... I've added weight and changed the weight distro and then gone back through and tried all these things again, all to no avail. I've tried high anti-roll bars, low, high in the front/low in the back, vice versa, middling values. I'm out of variables to play with.

Braking sensitivity on the LSD helps when its a really minor problem, but for cars like the DB3S with the Supercharger added it doesn't help at all, at least not in any configuration of LSD/Suspension/wight distro/brake balance I've tried. I've spent more time trying to tune this Aston today than I've spent actually playing the game in the last week, and Im not seeing any progress. What am I missing?

Any suggestions would be greatly appreciated. I'm not asking for the top tuners to tell me their secrets, I just want a nudge in the right direction so I feel like I'm actually getting somewhere with this recurring problem that's been plaguing my setups for months, though it's really coming to a head with the DB3S in particular.

I don't have the answer, but if no one here can help, probably worth asking in reddit granturismoopentunes ... they also have active discord group and I'm sure they'll have the answers to your question.

 

[bread82]

I don't own those cars (can't afford them yet!), so what I'm about to say is generic:

On a non aero car, consider playing with ride height differences front to rear. There's definitely an effect on handling and it may be "body aerodynamic" in nature. An E-type I just played with had differing behaviour on corner entry and exit, rake gave me turn in oversteer but exit understeer. You are getting a loose rear end on turn in, and different cars may require different settings, so I'd try both normal and reverse rake i.e Front/Rear 100mm/140mm then also try 140/100.

Try softening springs and dampers all around if its suddenly twitching. It may show the same behaviour, but slower, which makes control corrections easier. There's a point at which too soft becomes delayed and blobby but I generally prefer softer settings.

Brake balance and LSD decel are the usual big settings for this behaviour, as you have said, its weird that they've not helped you much. LSD decel especially for downshift judders.

Are you on racing tyres?