RE: RPM Technik 718 Cayman GT4 MR | PH Review
Discussion
GTRene said:
RacerMike said:
Have a look at my onboard from Sunday and tell me what's more of an issue. Mid corner instability or gearing....
That GT4 sounds great, also good power, is all standard or some little changes to engine tune/exhaust/inlet?RacerMike said:
HokumPokum said:
that looks pretty bad .
Can you describe what type of mid corner oversteer ie under what type of brake/throttle and which phase of the corner it usually appears? Tx
It’s mid corner as the car loads up and the rear starts to roll. You can ‘fix’ it by stopping roll. That means stiffest setting on the rear arb and more camber as a road car, or new dampers with the compression damping turned right up and highly aggressive static camber. The race cars basically do this, but for the road it doesn’t really work, but all you’re really doing is moving the behaviour further and further up the grip making it more and more snappy when it eventually gets there. It’s not uncommon to see people crash the race cars getting a huge stab of oversteer mid corner, and then flying off in the opposite direction as it grips up again.Can you describe what type of mid corner oversteer ie under what type of brake/throttle and which phase of the corner it usually appears? Tx
Autoquest in the US do an IRS kit and explain the kinematic issues very well.
https://www.autoquestcars.com/custom-09
Escy said:
Does the GT4RS have the same handling trait?
Must do to an extent as it’s still a strut on the rear. The Nurburgring lap seems to exhibit a few similarities like the way it seems to push quite a bit on some of the medium speed corners. More than likely the increased damper and sprint stiffness helps though. Edited to add, have a look at the second time this guy in a Clubsport race car goes through Radillion (about 3 mins on)…..
Edited by RacerMike on Tuesday 10th May 21:43
HokumPokum said:
Tx. Is there a particular style of driving to drive around the problem? Other than being slower of course
It’s more evident on the sprint lap there as there wasn’t a great deal of time to warm the tyres. Cup 2’s aren’t hugely progressive when cold, so the behaviour is made worse by then not having great temperature.It’s a tough one as the difference between over saturating the rear and not pushing enough is pretty small. However generally, carrying slightly less speed than you’d like into the apex helps.
The main issue is that if the cars moving around at all, you’re close to the point at which it starts to do this and it’s not so much the oversteer that’s the issue but the way it comes back. As the load disappears due to the rears sliding, the geometry improves and they grip up again! Hence the common crash in the race cars being a huge tank slapper in the other direction to the corner. So it makes it somewhat intimidating to drive hard.
RacerMike said:
It’s more evident on the sprint lap there as there wasn’t a great deal of time to warm the tyres. Cup 2’s aren’t hugely progressive when cold, so the behaviour is made worse by then not having great temperature.
It’s a tough one as the difference between over saturating the rear and not pushing enough is pretty small. However generally, carrying slightly less speed than you’d like into the apex helps.
The main issue is that if the cars moving around at all, you’re close to the point at which it starts to do this and it’s not so much the oversteer that’s the issue but the way it comes back. As the load disappears due to the rears sliding, the geometry improves and they grip up again! Hence the common crash in the race cars being a huge tank slapper in the other direction to the corner. So it makes it somewhat intimidating to drive hard.
Is the effect the same with all TC/ESC system turned off? It’s a tough one as the difference between over saturating the rear and not pushing enough is pretty small. However generally, carrying slightly less speed than you’d like into the apex helps.
The main issue is that if the cars moving around at all, you’re close to the point at which it starts to do this and it’s not so much the oversteer that’s the issue but the way it comes back. As the load disappears due to the rears sliding, the geometry improves and they grip up again! Hence the common crash in the race cars being a huge tank slapper in the other direction to the corner. So it makes it somewhat intimidating to drive hard.
hate those tank slappers...
you could get those as well with the Z3 M coupe's and wider tires and more power, could give some scary moments :-)
7 or so years ago I had such which also could land me in the rail guards, I thought, not now! so when the car came again in a saver 'direction/path'
I stomped on the brake hard and that saved me (and the car) :-)
you could get those as well with the Z3 M coupe's and wider tires and more power, could give some scary moments :-)
7 or so years ago I had such which also could land me in the rail guards, I thought, not now! so when the car came again in a saver 'direction/path'
I stomped on the brake hard and that saved me (and the car) :-)
Oz83 said:
Is the effect the same with all TC/ESC system turned off?
The stability control interventions are pretty late and don’t do an awful lot so yes. Don’t tend to drive it with everything off unless I’m on a big circuit like Silverstone and even then it barely really comes in until your already fairly sideways.I actually lead calibration of stability control for an OEM, and generally it’s a bit of a fallacy that it makes things worse if you’re reacting to the instability yourself. Very very early traction control only systems weren’t that great, but modern Stability Control is far quicker than the driver is if it’s calibrated properly but also won’t try and fully correct the vehicle. It’s there to stop the instability building and to give the driver time to react (or indeed not react!) but it won’t generally try and and target zero yaw until you turn into the slide at which point it will just do it’s best to help you correct the car proportionally to your input. It’s an open loop system that’s comparing vehicle behaviour to driver requests the whole time, and as such isn’t acting to try and second guess the driver.
Proper side slip control that can completely correct the car without the driver input do exist in prototype form, but the safety cases for these are hard to get into production because reliable measurement of vehicle yaw are notoriously difficult to do with productionised sensors.
This is Top End Modding-although it’s hard to understand why?
I also don’t understand how Porsche would have sold the car with the gearing issues in the first place.
What I do understand is that this is a showcase car for RPM. There’s tons of stuff you can do or have done.
How deep is your love? I mean pocket.
I have 14 Boxter S-I’m not sure it needs any mods.
I also don’t understand how Porsche would have sold the car with the gearing issues in the first place.
What I do understand is that this is a showcase car for RPM. There’s tons of stuff you can do or have done.
How deep is your love? I mean pocket.
I have 14 Boxter S-I’m not sure it needs any mods.
barchetta_boy said:
RacerMike said:
GT4 already has an LSD.
GT4 Clubsport race car has an e-diff with zero preload, effectively an open diff. Another weird decisionhttps://assets.porsche.com/motorsport/internationa...
I thought the GT4 just had the torque vectoring electronics.
There is a world of difference between an aftermarket diff and what OEM's fit. I've seen lots of Porsche owners complain their factory LSD is basically acting open after not much use. I wonder if a decent diff negates the handling trait in your video?
There is a world of difference between an aftermarket diff and what OEM's fit. I've seen lots of Porsche owners complain their factory LSD is basically acting open after not much use. I wonder if a decent diff negates the handling trait in your video?
Escy said:
I thought the GT4 just had the torque vectoring electronics.
There is a world of difference between an aftermarket diff and what OEM's fit. I've seen lots of Porsche owners complain their factory LSD is basically acting open after not much use. I wonder if a decent diff negates the handling trait in your video?
An LSD can’t solve handling issues due to kinematics. It can slow down yaw if it locks when you get oversteer but you’re only ever helping post limit stability. There is a world of difference between an aftermarket diff and what OEM's fit. I've seen lots of Porsche owners complain their factory LSD is basically acting open after not much use. I wonder if a decent diff negates the handling trait in your video?
A diff has zero effect on sub limit handling other than to increase traction in tight, low speed corners and promote understeer/push off throttle and on limit. The diff preload on most Porsche GT cars is pretty high and you can feel it when manoeuvring on loose surfaces. The car already understeers on power anyway, so more locking torque from the diff wouldn’t be what you want.
Torque vectoring is calibrated through brake torque control based on the yaw target. As you approach limit cornering, the ABS modulator can build brake pressure on the inside wheels to help turn the car. This is calibrateable during development, and can cause oversteer if it’s too strong, but that’s not what’s happening here the oversteer is directly related to roll rather than steering angle.
Hope my wordy responses are vaguely educational and not too difficult to understand. Definitely find that stability control/post limit/diff control is fairly poorly understood by the marketing departments in car companies, and by car enthusiasts. We’ve come a long way from early traction control and abs and it’s at the point where turning it off in many cars is pointless/not necessary for anyone unless you want to do big skids (and in some cases now, you can even select modes that allow and help you to do this whilst keeping some degree of safety net in place). The attitude of ‘just turn it off, it gets in the way’ is basically something that stems from magazine reviews of systems 25 years ago.
barchetta_boy said:
I think that misses the point completely. It's not about having to rev it out it's about being able to rev it out without going silly speeds. I have the 718 GTS which is the same drivetrain as the GT4 and I have booked in for the short gears at RPM. The car makes no sense as it is, you may as well move the red line down from 7750 to 6000.
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