Wet Bend=£ :(
- Thread starter dlknight
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Andy Duncan
New member
Make sure your wishbone ball joint is has not been damaged either.
You might get a new wheel out of it if you try hard enough!!
Hard lines.
andy
You might get a new wheel out of it if you try hard enough!!
Hard lines.
andy
Guest
New member
When you write "spun", do you mean that this was a rear-end slide where the car changed direction rapidly, or did you understeer off the road.
This question is not just morbid curiosity. A few years ago, I was involved (not in any official capacity - as an understanding engineer) in trying to establish the cause of a low-speed crash involving a 944. A lot of evidence pointed to a partial spin that was only partially caught by the driver being the cause of the accident. However, others would not accept this explanation, because the 944 just would not do that sort of thing. (A spin in a 911 would have been accepted at the drop of a hat!) At the time, some (presumably 911 owning) jokers in the US were calling this the "transaxle toss".
In the accident I was looking into, the car changed direction suddenly on a wet bend, crossed a pavement (thankfully empty) and ended up on the remains of a small brick wall. The driver was very experienced in driving rear-wheel-drive sports cars, and well aware from practical experince how to address limits of grip at both ends of a car. However, her clear testimony is that the car changed direction so fast that there was absolutely no chance of catching it. The evidence showed that she had managed to get a good amount of right-hand steering angle applied, although the accident took place on a left-hand curve, suggesting an intuitive correction to an oversteering car.
There was front suspension damage, but nothing was broken. The bend was tight in a built-up area, and the speed of the car was no more than 20mph before the accident. The driver had both hands on the steering wheel, and reported no sharp tug on the wheel. Anyone with any experience of a non-assisted 944 will know that this means that the front wheels did not hit the kerb - this would have caused a huge force at the steering wheel.
What is interesting is that there was a lot of evidence that the kerb was hit regularly. It was at a severe pinch point in a busy road, and all drivers will have to go very close to it if there is any traffic coming the other way. My best guess is that the car hit the kerb with the rear wheel and this caused it to snap into oversteer. With the back being knocked to the right, and the front having left lock, the car very rapidly spul left. The driver's efforts to correct this with right lock were probably never going to succeed.
My conclusion was that the correct finding was a minor driver error: clipping the kerb with a rear wheel. However, I also thought that the car did not handle this event well. The 944 has a large polar moment of inertia, so one any sort of spin happens, it is hard to gather up Also, they are not expected in a 944. In contrast, the 911 has a tiny polar moment of inertia, which means that tail spins can be gathered rather intuitively, if you keep your head, and as a driver, you are always ready for the back to go.
I really would like to get to the bottom of this. The 944 is such a well-handling car (I only wish my 911 handled as well) - but the 944 seems to have the occasional ability to get it badly worng - just sometimes. When I drove 944s, I did not know this! Every living (or very slow) 911 driver knows what not to do with the car. Everyone knows: "What not to do in a 911: Lift-off the throttle mid-corner if you are loosing it" and lots of other tips. There is no corresponding 944-llore. I think that it would be a Good Thing if a similar "What not to do in a 944..." could be developed.
Here is my contribution: What not to do in a 944: Use just a little too much power on a snow-covered road. You will find that the back can go sideways remarkably quickly, even at low speed. Getting into a tank-slapper is remarkably easy, and who knows which direction you will end up pointing! Done it twice :-( In contrast, 911s are quite good in snow (but feel utterly terrifying).
A
This question is not just morbid curiosity. A few years ago, I was involved (not in any official capacity - as an understanding engineer) in trying to establish the cause of a low-speed crash involving a 944. A lot of evidence pointed to a partial spin that was only partially caught by the driver being the cause of the accident. However, others would not accept this explanation, because the 944 just would not do that sort of thing. (A spin in a 911 would have been accepted at the drop of a hat!) At the time, some (presumably 911 owning) jokers in the US were calling this the "transaxle toss".
In the accident I was looking into, the car changed direction suddenly on a wet bend, crossed a pavement (thankfully empty) and ended up on the remains of a small brick wall. The driver was very experienced in driving rear-wheel-drive sports cars, and well aware from practical experince how to address limits of grip at both ends of a car. However, her clear testimony is that the car changed direction so fast that there was absolutely no chance of catching it. The evidence showed that she had managed to get a good amount of right-hand steering angle applied, although the accident took place on a left-hand curve, suggesting an intuitive correction to an oversteering car.
There was front suspension damage, but nothing was broken. The bend was tight in a built-up area, and the speed of the car was no more than 20mph before the accident. The driver had both hands on the steering wheel, and reported no sharp tug on the wheel. Anyone with any experience of a non-assisted 944 will know that this means that the front wheels did not hit the kerb - this would have caused a huge force at the steering wheel.
What is interesting is that there was a lot of evidence that the kerb was hit regularly. It was at a severe pinch point in a busy road, and all drivers will have to go very close to it if there is any traffic coming the other way. My best guess is that the car hit the kerb with the rear wheel and this caused it to snap into oversteer. With the back being knocked to the right, and the front having left lock, the car very rapidly spul left. The driver's efforts to correct this with right lock were probably never going to succeed.
My conclusion was that the correct finding was a minor driver error: clipping the kerb with a rear wheel. However, I also thought that the car did not handle this event well. The 944 has a large polar moment of inertia, so one any sort of spin happens, it is hard to gather up Also, they are not expected in a 944. In contrast, the 911 has a tiny polar moment of inertia, which means that tail spins can be gathered rather intuitively, if you keep your head, and as a driver, you are always ready for the back to go.
I really would like to get to the bottom of this. The 944 is such a well-handling car (I only wish my 911 handled as well) - but the 944 seems to have the occasional ability to get it badly worng - just sometimes. When I drove 944s, I did not know this! Every living (or very slow) 911 driver knows what not to do with the car. Everyone knows: "What not to do in a 911: Lift-off the throttle mid-corner if you are loosing it" and lots of other tips. There is no corresponding 944-llore. I think that it would be a Good Thing if a similar "What not to do in a 944..." could be developed.
Here is my contribution: What not to do in a 944: Use just a little too much power on a snow-covered road. You will find that the back can go sideways remarkably quickly, even at low speed. Getting into a tank-slapper is remarkably easy, and who knows which direction you will end up pointing! Done it twice :-( In contrast, 911s are quite good in snow (but feel utterly terrifying).
A
Guest
New member
Interesting thoughts re the accident. A must admit I've had my fair share of interesting tail out moments. Due to the weight distribution I would not expect a 944 to be quite as forgiving as say a nose heavy car were the rear end can be swung around further and retrieved from greater slip angles. Would imagine a 911 to be less forgiving still though?
The basic condition of the suspension has a very big impact on the handling, a 944 with shot dampers and were the alignment hasn't been checked in years can be a pretty hairy animal I know mine was befor I spent god knows how many man hours and rather too much money getting it all spruced back to something a little better than original condition
I still don't think the handling is quite as begnin as maybe an eighties three or five series BMW, which are easier to slide and hold in a slide but ultimate grip levels seemed lower.
In short I dont think there is an inherent flaw or a dangerous flaw just that the handling needs to be learnt and respected.
The basic condition of the suspension has a very big impact on the handling, a 944 with shot dampers and were the alignment hasn't been checked in years can be a pretty hairy animal I know mine was befor I spent god knows how many man hours and rather too much money getting it all spruced back to something a little better than original condition
I still don't think the handling is quite as begnin as maybe an eighties three or five series BMW, which are easier to slide and hold in a slide but ultimate grip levels seemed lower.
In short I dont think there is an inherent flaw or a dangerous flaw just that the handling needs to be learnt and respected.
My experience of both models in snow is that once the back gets moving it takes a long time to stop.![[FONT=verdana,geneva"]](/forum/styles/default/pcgb/space.gif ". [FONT=verdana,geneva\"]")
On a dry track both models are very easy to gather up when sideways. I never believed the whole 911 evil handling thing (at least not by the 3.2 Carrera era) - I think it is made up by owners who are scared of the car and trying to make themselves feel better about that by pretending nobody can "tame" it. When I bought my first one from Michael Ticehurst he said to me "if anyone tells you they deliberately provoke oversteer in a 911 they are a liar". Well, I had deliberate oversteer in mine on roundabouts on the way home, and many, many times after that, particularly memorably on repeated laps of Knockhill at the hairpin before the start line. Mine had an LSD which may have made all the difference, but I found it a very easy car to go sideways in, and I'm not trying to claim I'm Fangio nor anything like him. Sure you don't want to snap the throttle shut in mid bend (and I did that at KH once too), but you don't want to do that in any car when pressing on.
On a dry track both models are very easy to gather up when sideways. I never believed the whole 911 evil handling thing (at least not by the 3.2 Carrera era) - I think it is made up by owners who are scared of the car and trying to make themselves feel better about that by pretending nobody can "tame" it. When I bought my first one from Michael Ticehurst he said to me "if anyone tells you they deliberately provoke oversteer in a 911 they are a liar". Well, I had deliberate oversteer in mine on roundabouts on the way home, and many, many times after that, particularly memorably on repeated laps of Knockhill at the hairpin before the start line. Mine had an LSD which may have made all the difference, but I found it a very easy car to go sideways in, and I'm not trying to claim I'm Fangio nor anything like him. Sure you don't want to snap the throttle shut in mid bend (and I did that at KH once too), but you don't want to do that in any car when pressing on.
sawood12
New member
Mmmm. I think the lower polar moment of inertia of mid-engined cars make the cars much more twitchy - things happen faster. This means to me that if you loose it without expecting you are much more likely to end up in the ditch. On the other hand the 944's higher polar moment of inertial means the car lets go in a much slower and progressive manner (unless you are really driving like a ****) and as long as you don't let the back end get too out of shape before it's gathered up too much momentum, is more easily recovered. I'm no Pro dirver but i've had two unexpected 'moments' in my car and have easily recovered the wayward back end and almost enjoyed the experiance instead of filling my pants.
I think two rules I always follow are to make sure you do everything in smooth progressive way and in as much of a straight line as possible (i.e. good textbook driving technique) and the other is watch out for that boost - it's a hell of a kick in the back. The good thing about the 944 is that if you set the car up beforehand you can carry the speed into the corner rather than employing the classic 'slow in fast out' 911 technique. I think ultimately the 944 hasn't got 'carefree' handling like modern cars seem to have with all their electronic aids to get people out of trouble without them even knowing they were in trouble.
I think two rules I always follow are to make sure you do everything in smooth progressive way and in as much of a straight line as possible (i.e. good textbook driving technique) and the other is watch out for that boost - it's a hell of a kick in the back. The good thing about the 944 is that if you set the car up beforehand you can carry the speed into the corner rather than employing the classic 'slow in fast out' 911 technique. I think ultimately the 944 hasn't got 'carefree' handling like modern cars seem to have with all their electronic aids to get people out of trouble without them even knowing they were in trouble.
carlmthompson
New member
Hmmmm.
Sideways moments in the Porsche always cause me concern. Not because it's any harder or simpler than my BM to gather up, just that it would be a lot more gutting to cause damage, and in the Porsche, the grip levels are so much more, that sideways moments are at higher speeds (although in the wet the margin is lower).
I actually enjoy getting the BM sideways, but would only try it in the 44 when there's plenty of road to use.
Sideways moments in the Porsche always cause me concern. Not because it's any harder or simpler than my BM to gather up, just that it would be a lot more gutting to cause damage, and in the Porsche, the grip levels are so much more, that sideways moments are at higher speeds (although in the wet the margin is lower).
I actually enjoy getting the BM sideways, but would only try it in the 44 when there's plenty of road to use.
Guest
New member
Hmm, no sure about your definition of polar moment of inertia. I thought it was (mass) * (distance from the axis). If you lose the back end then the axis is the front wheels. In this case, the 944s engine mass won't count for much as it is almost over the axis, so it's only the gearbox weight you need to worry about. But the 911 has the lot right at the back, so much greater moment....?
Obviously I never have accidents. Worryingly though, since deciding to buy the 944 I have run into my father's car, a pot-hole full of water and rocks, and a big boulder (while reversing to look at the pothole). This does not bode well.
Obviously I never have accidents. Worryingly though, since deciding to buy the 944 I have run into my father's car, a pot-hole full of water and rocks, and a big boulder (while reversing to look at the pothole). This does not bode well.
Guest
New member
In the 911 most of the weight is at the back (gearbox and engine), so the centre of gravity is also near the back, hence the polar moment of inertia is quite small ((mass) * (distance from the centre of gravity)). In the 944, because the weight is at both the front and the back (engine and transaxle), the centre of gravity is somewhere near the middle of the car, so the weights are quite a distance from this centre of gravity. Probably.
Tom
Tom
Hi eurgain,
Well it was a bit of an S bend - chicane, normally go fairly quickly through it and most people cut the corners as its on a slight incline and you can see across both bends.
Went through the first (right hand) bend fairly quickly not lifting the throttle then turned into the second (left hand) bend and felt the car become very light
, then almost manage to get her straight again... but had a bit of "tank slap?" left to right motion from the back end which then turned into a 180 (back end came out to the left) and I slide into a bush on the side of the road...
I've had the back end out before (slower speeds) and its always pulled back into line without any encouragement...
Dave K.
Well it was a bit of an S bend - chicane, normally go fairly quickly through it and most people cut the corners as its on a slight incline and you can see across both bends.
Went through the first (right hand) bend fairly quickly not lifting the throttle then turned into the second (left hand) bend and felt the car become very light
, then almost manage to get her straight again... but had a bit of "tank slap?" left to right motion from the back end which then turned into a 180 (back end came out to the left) and I slide into a bush on the side of the road...I've had the back end out before (slower speeds) and its always pulled back into line without any encouragement...
Dave K.
NeilW
New member
Other than in the snow I've only really lost the back end in a big way once. It was after only a few weeks of 944 ownership, which marked a return to rear wheel drive after many years in FWD. I'd become familiar with the car in the dry and was quite rightly impressed with it's handling and grip. On one of the first few wet days shortly after I decided to 'test' it a little using a roundabout near where I live. In second gear I floored the throttle exiting the roundabout leading onto the slip road. There is a change of direction and of pitch during at which time the car reached 4,000rpm, which as you know in an 'S' is when most of the power arrives. The car immediately snapped sideways, far quicker than I was expecting. In fact I'd been expecting the car to cope with this and not slide at all. Anyway, applied the opposite lock, but too much, and immediately got into a tank slapper. Luckily, very luckily, managed to get the car to a standstill in a straight line without hitting anything though not necessarily pointing in the right direction! Conclusion: what is a benign handling car in the dry will bite you badly in the wet.
Diver944
Active member
I think the 50-50 weight means that if you do lose it unexpectedly then its pretty hard to get back unless your used to doing it. I also think an LSD helps get things back under control quicker.
When I used to track the non-LSD S2 I lost the back end twice on damp surfaces and both times I caught it but overcorrected the other way which resulted in a further 100 yards of tankslapping before finally coming to a halt after a 180 degree sspin. Embaressingly I have a video of one of these times [:-]
I have only seriously lost the back end of the LSD equipped Turbo once in the damp and this was travelling around the first corner Copse at Silverstone in 4th gear. I thought a big moment was about to happen but a slight lift with some opposite lock and the car collected it all up with no fuss.
All three of these times have been on track when pushing on a bit. I may be an old fuddy duddy but I simply don't understand how a 944 can be lost so easily on the road. The example of a 20mph slide from a kerbed wheel is quite scarey to think of if you imagine a car coming the other way at the same time []
When I used to track the non-LSD S2 I lost the back end twice on damp surfaces and both times I caught it but overcorrected the other way which resulted in a further 100 yards of tankslapping before finally coming to a halt after a 180 degree sspin. Embaressingly I have a video of one of these times [:-]
I have only seriously lost the back end of the LSD equipped Turbo once in the damp and this was travelling around the first corner Copse at Silverstone in 4th gear. I thought a big moment was about to happen but a slight lift with some opposite lock and the car collected it all up with no fuss.
All three of these times have been on track when pushing on a bit. I may be an old fuddy duddy but I simply don't understand how a 944 can be lost so easily on the road. The example of a 20mph slide from a kerbed wheel is quite scarey to think of if you imagine a car coming the other way at the same time [
]
sawood12
New member
The best way to visuallise the effects of polar moment of inertia is image that in one hand you have a dumbell with 5kg's on it and the other hand you have a barbell with 5kg's on it. Now if you try to rotate them you'll find the dumbell with move quickly with very little effort whereas the barbell will need alot more force to rotate, it will rotate with much slower accellaration and will be much harder to bring to a halt.
A mid engined car is a dumbell and a 944 is a barbell. The effect of this assuming you have two cars of equal weight but one is a mid engined car and the other a 944 going round a given bend at the same speed under the same conditions. The forces on both cars are the same. If the mid-engined car breaks it will break much more quickly than the 944. If (and I mean if) you are fast enough to catch the mid engined car it will be easier to bring back into line. With the 944 when the car breaks it will break in a much more progressive manner but as soon as it breaks it will begin to gather up momentum and so the longer it takes you to regain control the more difficult it will be to do so.
That is why F1 cars are so difficult to drive - they have such a low polar moment of inertia if the vast majority of us normal people just jumped into one we wouldn't be quick enough to deal with it's twitchiness. It is also why there are alot of Lotus Elises written off - very light car + mid engined = very twitchy car.
Ideally you want a mix of both (for safer road use at least) - a mid engined car to get a good polar moment of inertia and therefore good handling (quick change of direction) but the more progressive nature of the 944 configuration. A classic engineering problem.
A mid engined car is a dumbell and a 944 is a barbell. The effect of this assuming you have two cars of equal weight but one is a mid engined car and the other a 944 going round a given bend at the same speed under the same conditions. The forces on both cars are the same. If the mid-engined car breaks it will break much more quickly than the 944. If (and I mean if) you are fast enough to catch the mid engined car it will be easier to bring back into line. With the 944 when the car breaks it will break in a much more progressive manner but as soon as it breaks it will begin to gather up momentum and so the longer it takes you to regain control the more difficult it will be to do so.
That is why F1 cars are so difficult to drive - they have such a low polar moment of inertia if the vast majority of us normal people just jumped into one we wouldn't be quick enough to deal with it's twitchiness. It is also why there are alot of Lotus Elises written off - very light car + mid engined = very twitchy car.
Ideally you want a mix of both (for safer road use at least) - a mid engined car to get a good polar moment of inertia and therefore good handling (quick change of direction) but the more progressive nature of the 944 configuration. A classic engineering problem.
mik_ok
New member
Nice summary Scott.
I believe an LSD adds a level of consistancy also. A hefty dollop of power in a car with an LSD will cause more torque than both rears can cope with, and you will get oversteer.
Without an LSD, the above scenario usually results in the inner wheel spinning, and no oversteer.
Occaisionally both wheels will hook up however and give you (relatively) snappy oversteer. Not sure if this is a spinning inner wheel that finds grip and forces the outer to break away quite suddenly (?).
I've had the rear end of the S2 out in the wet on a number of occaisions (all power oversteer). Several times when that was exactly what I was intending to do. A few when not. More often than not the unintended slides have been quite snappy.
As I've said before, the one option I would like over my S2's current spec is an LSD.
I believe an LSD adds a level of consistancy also. A hefty dollop of power in a car with an LSD will cause more torque than both rears can cope with, and you will get oversteer.
Without an LSD, the above scenario usually results in the inner wheel spinning, and no oversteer.
Occaisionally both wheels will hook up however and give you (relatively) snappy oversteer. Not sure if this is a spinning inner wheel that finds grip and forces the outer to break away quite suddenly (?).
I've had the rear end of the S2 out in the wet on a number of occaisions (all power oversteer). Several times when that was exactly what I was intending to do. A few when not. More often than not the unintended slides have been quite snappy.
As I've said before, the one option I would like over my S2's current spec is an LSD.
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