Locking rear diff on C4 -understeer
06-27-2012, 10:42 PM
#16
Rennlist Member
+1 on Makmov and others. I'd think 3X before I go and disconnect engineering that was thought out so carefully. I got help from Steve W. at Rennsport and my car is completely neutral.
Also you might want to read up on the Porsche Allrad book (1900-1990 the Development of Porsche All Wheel Drive) where they have lengthy articles (some poorly translated) that describe the work that went into a superior AWD system...
I understand you wanting to address the understeer, but IMHO, disconnecting that kind of thing seems a bit drastic.
Also you might want to read up on the Porsche Allrad book (1900-1990 the Development of Porsche All Wheel Drive) where they have lengthy articles (some poorly translated) that describe the work that went into a superior AWD system...
I understand you wanting to address the understeer, but IMHO, disconnecting that kind of thing seems a bit drastic.
06-28-2012, 12:08 AM
#17
Burning Brakes
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Jack, what year is your C4? I believe early C4's had 18mm rear bars but 1991 cars on had a 20mm rear bar, which is much closer to the C2 21mm bar people usually swap to reduce under steer. I don't know if swapping the rear bar on a later C4 makes much difference?? Would be interested to know what others think?
06-28-2012, 01:44 AM
#18
Pro
Hi
I wish I had known this when I had my 964 (in the years before the Internet). Having said that I did have a Porsche Teknik suspension fitted and I think that did include revised roll bars. It did pretty much get rid of the understeer.
Berni
I wish I had known this when I had my 964 (in the years before the Internet). Having said that I did have a Porsche Teknik suspension fitted and I think that did include revised roll bars. It did pretty much get rid of the understeer.
Berni
06-28-2012, 06:08 AM
#19
Burning Brakes
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Jack, what year is your C4? I believe early C4's had 18mm rear bars but 1991 cars on had a 20mm rear bar, which is much closer to the C2 21mm bar people usually swap to reduce under steer. I don't know if swapping the rear bar on a later C4 makes much difference?? Would be interested to know what others think?
06-28-2012, 06:28 AM
#20
Three Wheelin'
Thread Starter
I understood that this was the case. Looked into changing the rear bar on mine when I overhauled the suspension ans was told not to bother on my '92 as the roll bar is already 'upgraded'. With H&R Greens, HDs, strut brace, 225s up front and a good set-up mine just wants to turn in. Feels very lively. Will understeer if the PDAS kicks in, but that has only happened when I have been clumsy and has probably saved my stupid neck.
06-28-2012, 06:36 AM
#21
Three Wheelin'
Thread Starter
I second Scott's motion.
It's worth also taking into consideration that it is only at the limit that these cars will under steer. This limit is unlikely in my mind to be truly exploited on public roads. A point that Adrian Crawford had expressed in his 964 book.
I would say that if you are experiencing understeer on the road I would suggest two options:
Have the alignment checked or spend more time learning the characteristics of your car. 911s require a very specific approach to driving.
It's worth also taking into consideration that it is only at the limit that these cars will under steer. This limit is unlikely in my mind to be truly exploited on public roads. A point that Adrian Crawford had expressed in his 964 book.
I would say that if you are experiencing understeer on the road I would suggest two options:
Have the alignment checked or spend more time learning the characteristics of your car. 911s require a very specific approach to driving.
As mentioned the Geo has just been done and set to RS spec. This has definitely helped but not eliminated it.
Take on board what you say about driving style but I appreciate the slow in, fast out method and the car still understeers on the limit.
It is not a big issue but I am interested in seeing if it can be approached by looking at the PDAS, particularly if it can just be deactivated with the button as described. I am a bit nervous about testing it out on a public road however in case it does make the car dangerous.
06-28-2012, 07:24 AM
#23
Three Wheelin'
With the PDAS disabled its only going to be as dangerous as any other 4wd car with open diffs - well one with the engine in the wrong place. Or for that matter as dangerous as an enabled PDAS system with worn out diff clutch plates - which after twenty years you'd figure most are?!
From what I've read the "traction control" effect is applied separately (based on different sensor inputs) and in a different way from the "antispin" control and the way the two systems modulate the centre and rear diffs is different (note the front diff is always open). So its perhaps a bit simplistic of Project 9 to say its the rear diff locking that's the issue....
I've got a 89 C4, bilsteins, H&R greens and a 22mm rear bar, that felt pretty good an neutral and then I got the RS settings put on it and I got the understeer back in some conditions. I didn't feel it anywhere around Spa but full throttle roundabout exits can often get the front to "wash out" rather - so its about weight transfer I think. GT-One pointed out my front ARB drop links were worn which they felt may be the issue as they were adament the RS settings were good for a C4 - personally I can't see how the same geo settings can be "just right" for a C4 and a C2 but there you go
Anyway the droplinks have no play but I noticed recently the ARB bushes are shot - so I have some poly ones waiting to go in and I'll let you know if that improves things.
I don't know if you've read the "wringing out the c4" article (google it) - which advocates the throw and catch method of cornering which is somewhat more aggressive than the traditional slow in fast out. I instinctively have started to use this myself to hussle the car a bit more through the corners - not in a way that would be advisable in a C2 I think - and I think it gave the BAT instructor at Spa a few sphincter tightening moments and he advised gentler inputs on brakes and steering at corner entry.
From what I've read the "traction control" effect is applied separately (based on different sensor inputs) and in a different way from the "antispin" control and the way the two systems modulate the centre and rear diffs is different (note the front diff is always open). So its perhaps a bit simplistic of Project 9 to say its the rear diff locking that's the issue....
I've got a 89 C4, bilsteins, H&R greens and a 22mm rear bar, that felt pretty good an neutral and then I got the RS settings put on it and I got the understeer back in some conditions. I didn't feel it anywhere around Spa but full throttle roundabout exits can often get the front to "wash out" rather - so its about weight transfer I think. GT-One pointed out my front ARB drop links were worn which they felt may be the issue as they were adament the RS settings were good for a C4 - personally I can't see how the same geo settings can be "just right" for a C4 and a C2 but there you go
Anyway the droplinks have no play but I noticed recently the ARB bushes are shot - so I have some poly ones waiting to go in and I'll let you know if that improves things.I don't know if you've read the "wringing out the c4" article (google it) - which advocates the throw and catch method of cornering which is somewhat more aggressive than the traditional slow in fast out. I instinctively have started to use this myself to hussle the car a bit more through the corners - not in a way that would be advisable in a C2 I think - and I think it gave the BAT instructor at Spa a few sphincter tightening moments and he advised gentler inputs on brakes and steering at corner entry.
06-28-2012, 08:40 AM
#24
Burning Brakes
Well,
i´ve the H&R Sway with hard setting in the rear. My H&R coilover is in the front round about 20 - 25mm lower adjusted than RS. In the back, the car seem to be just 15 - 20 mm lower than RS.
I´ve 225er on 7,5 rims in the front. Setting is like RS, but instead the 1° camber i´ve 1° 45' in the front ant front-toe is nearly neutral (like toe 0).
This setting is great. I don´t know if this is xx seconds faster than other settings but it feels absolute neutral when cornering. Front is rock solid. Playing with the brake pedal when turn-in to apex and the car is great, then turn-around and flat out. Or, when the radius is wider, playing with trottle during the slow part of the corner, the backend of the car "turns in" a little bit...
i´ve the H&R Sway with hard setting in the rear. My H&R coilover is in the front round about 20 - 25mm lower adjusted than RS. In the back, the car seem to be just 15 - 20 mm lower than RS.
I´ve 225er on 7,5 rims in the front. Setting is like RS, but instead the 1° camber i´ve 1° 45' in the front ant front-toe is nearly neutral (like toe 0).
This setting is great. I don´t know if this is xx seconds faster than other settings but it feels absolute neutral when cornering. Front is rock solid. Playing with the brake pedal when turn-in to apex and the car is great, then turn-around and flat out. Or, when the radius is wider, playing with trottle during the slow part of the corner, the backend of the car "turns in" a little bit...
06-28-2012, 01:53 PM
#25
With the PDAS disabled its only going to be as dangerous as any other 4wd car with open diffs - well one with the engine in the wrong place. Or for that matter as dangerous as an enabled PDAS system with worn out diff clutch plates - which after twenty years you'd figure most are?!
From what I've read the "traction control" effect is applied separately (based on different sensor inputs) and in a different way from the "antispin" control and the way the two systems modulate the centre and rear diffs is different (note the front diff is always open). So its perhaps a bit simplistic of Project 9 to say its the rear diff locking that's the issue....
I've got a 89 C4, bilsteins, H&R greens and a 22mm rear bar, that felt pretty good an neutral and then I got the RS settings put on it and I got the understeer back in some conditions. I didn't feel it anywhere around Spa but full throttle roundabout exits can often get the front to "wash out" rather - so its about weight transfer I think. GT-One pointed out my front ARB drop links were worn which they felt may be the issue as they were adament the RS settings were good for a C4 - personally I can't see how the same geo settings can be "just right" for a C4 and a C2 but there you go Anyway the droplinks have no play but I noticed recently the ARB bushes are shot - so I have some poly ones waiting to go in and I'll let you know if that improves things.
I don't know if you've read the "wringing out the c4" article (google it) - which advocates the throw and catch method of cornering which is somewhat more aggressive than the traditional slow in fast out. I instinctively have started to use this myself to hussle the car a bit more through the corners - not in a way that would be advisable in a C2 I think - and I think it gave the BAT instructor at Spa a few sphincter tightening moments and he advised gentler inputs on brakes and steering at corner entry.
From what I've read the "traction control" effect is applied separately (based on different sensor inputs) and in a different way from the "antispin" control and the way the two systems modulate the centre and rear diffs is different (note the front diff is always open). So its perhaps a bit simplistic of Project 9 to say its the rear diff locking that's the issue....
I've got a 89 C4, bilsteins, H&R greens and a 22mm rear bar, that felt pretty good an neutral and then I got the RS settings put on it and I got the understeer back in some conditions. I didn't feel it anywhere around Spa but full throttle roundabout exits can often get the front to "wash out" rather - so its about weight transfer I think. GT-One pointed out my front ARB drop links were worn which they felt may be the issue as they were adament the RS settings were good for a C4 - personally I can't see how the same geo settings can be "just right" for a C4 and a C2 but there you go
Anyway the droplinks have no play but I noticed recently the ARB bushes are shot - so I have some poly ones waiting to go in and I'll let you know if that improves things.I don't know if you've read the "wringing out the c4" article (google it) - which advocates the throw and catch method of cornering which is somewhat more aggressive than the traditional slow in fast out. I instinctively have started to use this myself to hussle the car a bit more through the corners - not in a way that would be advisable in a C2 I think - and I think it gave the BAT instructor at Spa a few sphincter tightening moments and he advised gentler inputs on brakes and steering at corner entry.
07-01-2012, 02:17 PM
#30
Rennlist Member
Ok this may be utter rubbish I am no expert but I have owned my car for 8 years and this is my feeling in under steer on the C4
There are two types of under steer.
1)the cars natural tendency to under steer more than a C2. this can be almost eliminated with anti roll bars, geo set up etc etc.
2) The PDAS system when it kicks in. this may not be described very well but I'll give it a go.
Its quite obvious to me that when this happens you get an 'Artificial' under steer that is far worse than any under steer in any car. It actually reminds of those cars they use to teach you how to get out of skids.
This can be driven around. In fact I don't remember the last time I had this. When I first got the car I had it quite a lot.
Caused by me flooring it before the apex no doubt on very tight roundabouts.
the car then under steers like you wont believe the absolute wrong thing to do in that case is what you normally do for under steer i.e steer more towards where you want to go because then you get snap over steer and spin.
What you need to do is either dab the brake ( something I have not managed to try)
Or steer into the under steer ( as if you had over steer) which cuts the PDAS artificial under steer and preempts the snap over steer. When this works it works really well.
However like I said driving the car in a different manor now I don't get the PDAS to kick in anymore.