Solving terminal understeer in 500 bhp TVR Tuscan...
Discussion
.. in Gran Turismo 4.
So I've got myself a lightened, fettled TVR Tuscan. Front engined, 519bhp, rear wheel drive, <1000 kg, mild racing tyres, all driving aids dialled to 0.
Can I get the bastard to turn in? nope. Won't even donut.
Turn in feels woolly or not there at all, applying more power just winds on more understeer, lift off oversteer is non-existent. Just feels like there's no momentum to play with.
So the theory goes, GT4 is near as dammit reflection of 'true' driving dynamics. Lets go with the assumption that regardless of the actual physics employed the simulation reflects real world behaviour enough for real world solutions to have the same effects.
My understanding would be that in the 'real' world, for a benignly set up vehicle (assuming you've straight line braked to entry speed), on turn-in you'll experience mild understeer as you approach/cross the limit of front tyres adhesion. Application of either a weight transfer by lift off, or breaking traction at the rear with a bootful, should cause the rear to swing round, thereby tightening your line. I'm not really talking about drifting here, although that would be nice, just getting the weight transfer working for me.
Is it possible that they've modelled the car so accurately that in such a lightweight body, the weight of the engine in front is distorting the cars handling to that degree? Are lightweight cars in the real world similary afflicted by lack of momentum as a tool to alter line? After going to all that effort to lighten a vehicle it seems madness to add mass/ballast just to create polar momentum? Is it just a characteristic of Front engined/rear wheel drive overpowered light weights?
I guess the question here for those of you who do this stuff in the real world/know what you're talking about is what tweaks would you make to 'dial out' understeer and enable a more mobile rear end?
So I've got myself a lightened, fettled TVR Tuscan. Front engined, 519bhp, rear wheel drive, <1000 kg, mild racing tyres, all driving aids dialled to 0.
Can I get the bastard to turn in? nope. Won't even donut.
Turn in feels woolly or not there at all, applying more power just winds on more understeer, lift off oversteer is non-existent. Just feels like there's no momentum to play with.
So the theory goes, GT4 is near as dammit reflection of 'true' driving dynamics. Lets go with the assumption that regardless of the actual physics employed the simulation reflects real world behaviour enough for real world solutions to have the same effects.
My understanding would be that in the 'real' world, for a benignly set up vehicle (assuming you've straight line braked to entry speed), on turn-in you'll experience mild understeer as you approach/cross the limit of front tyres adhesion. Application of either a weight transfer by lift off, or breaking traction at the rear with a bootful, should cause the rear to swing round, thereby tightening your line. I'm not really talking about drifting here, although that would be nice, just getting the weight transfer working for me.
Is it possible that they've modelled the car so accurately that in such a lightweight body, the weight of the engine in front is distorting the cars handling to that degree? Are lightweight cars in the real world similary afflicted by lack of momentum as a tool to alter line? After going to all that effort to lighten a vehicle it seems madness to add mass/ballast just to create polar momentum? Is it just a characteristic of Front engined/rear wheel drive overpowered light weights?
I guess the question here for those of you who do this stuff in the real world/know what you're talking about is what tweaks would you make to 'dial out' understeer and enable a more mobile rear end?
In GT, the easiest way to get oversteer I've found it to drop and soften the front, and to raise and stiffen the back end.
FWIW, in terms of drifting, GT3 is way more fun. I can hold drifts all the way round superspeedway's corners, and given a powerful enough car (1000bhp Supra on sim tires), can keep the wheels spinning through a whole lap.
FWIW, in terms of drifting, GT3 is way more fun. I can hold drifts all the way round superspeedway's corners, and given a powerful enough car (1000bhp Supra on sim tires), can keep the wheels spinning through a whole lap.
I'd tried mucking about with weight balance, dialling it all to rear and adding some ballast there.
already had 3 degrees on fronts and .5 on rear camber. hadn't tried toe-in.
I'll try ride height and changing damping rates.
Guess I'm kind of daunted by the sheer array of tweaks possible, hence looking for expertise.
I'm also running an NSX-R and the difference is incredible which is what made me concentrate around MR/FR and weigh configuration.
already had 3 degrees on fronts and .5 on rear camber. hadn't tried toe-in.
I'll try ride height and changing damping rates.
Guess I'm kind of daunted by the sheer array of tweaks possible, hence looking for expertise.
I'm also running an NSX-R and the difference is incredible which is what made me concentrate around MR/FR and weigh configuration.
brotherharry said:
I'd tried mucking about with weight balance, dialling it all to rear and adding some ballast there.
It should be around 50:50, and you shouldn't need to move it (realistically you shouldn't be *able* to move it significantly). Can you spin the wheels? If not, the model is wrong. With that much power you should be able to smoke the tyres on demand in the lower gears. There will be an understeer region if the car is set up correctly, but you should have no trouble driving round it.
I'm wondering if there's another setting or option somewhere I'm missing because as you say with that much power...
I can get wheel spin happily in first three gears, what's not happening is the impression of weight transfer and impacts of loss of traction in the corners.
It's not the overall engine as other cars are 'behaving' and doing what I'd expect. Just something about the model of front/rear + power.
Just had a thought. If the rear was too soft, applying power would lift the front, meaning less traction, explaining why a bootful mid-corner just makes it worse. hmmm.
I can get wheel spin happily in first three gears, what's not happening is the impression of weight transfer and impacts of loss of traction in the corners.
It's not the overall engine as other cars are 'behaving' and doing what I'd expect. Just something about the model of front/rear + power.
Just had a thought. If the rear was too soft, applying power would lift the front, meaning less traction, explaining why a bootful mid-corner just makes it worse. hmmm.
Have you tried slowing down further than you'd expect to? I had this problem, especially with the stock Ruf; at what I thought was a reasonable speed it'd plough on for England... er, Germany. A bit less speed and it'd tuck in neatly, and dependent on throttle would either slingshot itself out of the corner or spend most of the curve impressively sideways.
GT4's tyre simulation is a little bit suspect in terms of how much lateral grip a tyre loses when spinning; it's most obvious when trying to perform doughnuts, but even in general GT4 driving a powerful RWD car doesn't exactly "snap" round when you floor the throttle in a slow corner, unless you've set it up beforehand for comedy tail-out action.
This works both ways, as it's a lot easier to hoon round a corner with the brakes "locked" than it ought to be.
The fidelity of the simulation is overall good, especially for the platform, but you do see odd things that aren't quite right. This is especially true when getting to extremes - 350bhp front wheel drive car that oversteers on full throttle, anyone?
GT4's tyre simulation is a little bit suspect in terms of how much lateral grip a tyre loses when spinning; it's most obvious when trying to perform doughnuts, but even in general GT4 driving a powerful RWD car doesn't exactly "snap" round when you floor the throttle in a slow corner, unless you've set it up beforehand for comedy tail-out action.
This works both ways, as it's a lot easier to hoon round a corner with the brakes "locked" than it ought to be.
The fidelity of the simulation is overall good, especially for the platform, but you do see odd things that aren't quite right. This is especially true when getting to extremes - 350bhp front wheel drive car that oversteers on full throttle, anyone?
Timberwolf said:
Have you tried slowing down further than you'd expect to?
That was my first schoolboy error and resulted in lots of comedy gravel plouging. I'm using standard controllers so with the touch sensitive braking keys (I use R2) took a while to twig I was just locking up the fronts every time. Just trying to judge braking distances I still don't have down properly. Thinking about it I have a sense of corning forces when playing, but not acceleration/decceleration.Dont' think it models ABS (shouldn't on a TVR anyway). I feel another late night coming on.
Was previously using only the mid-level suspension, so bought the full racing kit. Tried tweaking up suspension settings as suggested above. Tried out two levels, one more extreme than the other.
Softened front, hardened rear, added toe out and camber settings.
Turn was improved, reasonably but not massively. It really seems to be a problem in higher speed or tighter radius corners where a lift should induce oversteer. There's something not right about the momentum transfer I think
setting 1
setting 2
Softened front, hardened rear, added toe out and camber settings.
Turn was improved, reasonably but not massively. It really seems to be a problem in higher speed or tighter radius corners where a lift should induce oversteer. There's something not right about the momentum transfer I think
setting 1
setting 2
brotherharry said:
Was previously using only the mid-level suspension, so bought the full racing kit. Tried tweaking up suspension settings as suggested above. Tried out two levels, one more extreme than the other.
Softened front, hardened rear, added toe out and camber settings.
Turn was improved, reasonably but not massively. It really seems to be a problem in higher speed or tighter radius corners where a lift should induce oversteer. There's something not right about the momentum transfer I think
setting 1
setting 2
Softened front, hardened rear, added toe out and camber settings.
Turn was improved, reasonably but not massively. It really seems to be a problem in higher speed or tighter radius corners where a lift should induce oversteer. There's something not right about the momentum transfer I think
setting 1
setting 2
omg thats some dodgy setup.lol
drop the rear spring rate to about the same or slight less than the front. can raise it up a bit too.
drop the damper settings so bound is less than rebound by about 2(6/8 front, 6/8 rear or 5/7)
thats positive camber, the tops of the wheels pointing OUT, you want negative, and you dont want that much, try -2 front and -1.5 rear.
rear toe, set to +1 or 2.
lower the ARB settings to about 3.
You shouldn't have to change suspension geometry to 'allow' the back end to step out when you floor it - seems it's rather a basic flaw in the GT4 'physics' engine. Now if you were to try that in a proper driving sim (like GPL, GTL, rFacter etc) you would be going backward through hedges like there was no tomorrow! 
This intrigued me enough to dig out GT4 and have a bit of a try. Tuscan lightened as much as possible, power up to somewhere around 530bhp, semi-racing suspension and nearly all types of tyre bought.
Impressions from a lap or two of Apricot Hill...
N1 Slithery as anything. Understeer/oversteer, poor turn in. Dumping the throttle does very little to the car at all, which is surprising, but as mentioned GT4 is a bit funky when it comes to loss of lateral grip from high slip ratio especially at low speed.
N2 Fairly good handling, understeer when entering corners too fast but otherwise balanced or mildly oversteery. Back end steps out with heavy throttle application, although much more gently than I'd have thought - more like a heavy car with an open diff.
N3 Like the N2 but a bit sharper, a bit more tail-happy and more prepared to step out on the throttle.
N1-N3 roughly correspond to a range of tyres from budget road tyres up to soft (but road legal) track day compounds. Next we have the Sport tyres, commonly accepted to represent slicks when applied to production cars.
Sport I'll deal with these in one hit. Car responds very quickly and sharply to all inputs. Back end begins to get slithery, and tends towards full-on lairiness when booting the throttle. Lots of grip available. Tendency to turn in sharper and oversteer gets more pronounced the softer the tyre.
Then we have the racing tyres - or perhaps they should be called physics-beaters? I've found that when applying these to cars, they absolutely don't care in the slightest about getting loaded or unloaded. You can stick them on a barge with jelly suspension and it'll still corner at 1.5g, rolling to completely crazy angles of lean.
Racing Hard Similar to the softest sport tyres in terms of turn-in, but sustained grip is far higher allowing for suicidal corner exit speeds. Oversteer is reduced. The tendency to step out the tail on harder throttle applications is also disappearing as the car finds traction most of the time.
Racing Soft Turn-in is quite sharp, but most of the oversteer is gone now and it takes a kerb to upset the car. Inducing anything with a boot on the throttle is right out - the car just finds a way to get all 500-odd bhp to the ground and goes. As it accelerates, terminal understeer starts to set in; but the force meter is pinned hard against the 2g mark by this point.
My impression is that if you're using racing tyres, you've simply got more grip than should be possible. I didn't upgrade to a tighter LSD for this run, but if that's fitted as well then the sheer amount of grip available at the rear could be pushing the front wide.
I've never been that keen on the racing tyres for production cars anyway. They're great fun for hooning past the AI on the way to an enormous margin of victory or pulling 2g+ in an otherwise standard Volvo 240, though.
Impressions from a lap or two of Apricot Hill...
N1 Slithery as anything. Understeer/oversteer, poor turn in. Dumping the throttle does very little to the car at all, which is surprising, but as mentioned GT4 is a bit funky when it comes to loss of lateral grip from high slip ratio especially at low speed.
N2 Fairly good handling, understeer when entering corners too fast but otherwise balanced or mildly oversteery. Back end steps out with heavy throttle application, although much more gently than I'd have thought - more like a heavy car with an open diff.
N3 Like the N2 but a bit sharper, a bit more tail-happy and more prepared to step out on the throttle.
N1-N3 roughly correspond to a range of tyres from budget road tyres up to soft (but road legal) track day compounds. Next we have the Sport tyres, commonly accepted to represent slicks when applied to production cars.
Sport I'll deal with these in one hit. Car responds very quickly and sharply to all inputs. Back end begins to get slithery, and tends towards full-on lairiness when booting the throttle. Lots of grip available. Tendency to turn in sharper and oversteer gets more pronounced the softer the tyre.
Then we have the racing tyres - or perhaps they should be called physics-beaters? I've found that when applying these to cars, they absolutely don't care in the slightest about getting loaded or unloaded. You can stick them on a barge with jelly suspension and it'll still corner at 1.5g, rolling to completely crazy angles of lean.
Racing Hard Similar to the softest sport tyres in terms of turn-in, but sustained grip is far higher allowing for suicidal corner exit speeds. Oversteer is reduced. The tendency to step out the tail on harder throttle applications is also disappearing as the car finds traction most of the time.
Racing Soft Turn-in is quite sharp, but most of the oversteer is gone now and it takes a kerb to upset the car. Inducing anything with a boot on the throttle is right out - the car just finds a way to get all 500-odd bhp to the ground and goes. As it accelerates, terminal understeer starts to set in; but the force meter is pinned hard against the 2g mark by this point.
My impression is that if you're using racing tyres, you've simply got more grip than should be possible. I didn't upgrade to a tighter LSD for this run, but if that's fitted as well then the sheer amount of grip available at the rear could be pushing the front wide.
I've never been that keen on the racing tyres for production cars anyway. They're great fun for hooning past the AI on the way to an enormous margin of victory or pulling 2g+ in an otherwise standard Volvo 240, though.
Thanks chaps.
My mistake on the toe, will try flipping the other way. The other settings are probably more extreme as a result of me trying to get easily discernable effects.
Will also experiment with tyres, currently on R3 + a 2 way LSD.
Wonder if racing on front for grip and a sport level on rear will help.
I'm prepared for there to be some glitchery in the engine, but other stuff in the garage 'behaves' as it should, hence my conviction it's more about setup.
Might also try similar exercise in the T350c or something else lightweight.
My mistake on the toe, will try flipping the other way. The other settings are probably more extreme as a result of me trying to get easily discernable effects.
Will also experiment with tyres, currently on R3 + a 2 way LSD.
Wonder if racing on front for grip and a sport level on rear will help.
I'm prepared for there to be some glitchery in the engine, but other stuff in the garage 'behaves' as it should, hence my conviction it's more about setup.
Might also try similar exercise in the T350c or something else lightweight.
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