Handling characteristics

[Guest]

I have noticed the following:

If you go into a corner on a trailing throttle or nervously, the car takes a wider line (understeers).
If you go into a corner accelerating, the car tightens its line.
This is the opposite way round to most other cars, where more power equals more understeer (until under severe provocation the back lets go).
It took me a while to work this out. When it was new I tended to be a little more timid and had trouble predicting the line it would take.
I put this down to weight transference, i.e. when slowing the additional weight at the front causes the front to run wide.

If you drive round a corner the car is well balanced.[] Due to the larger tyres it requires a bit of throttle to get it round without losing speed.

The front bounces a bit when going down lumpy B/C roads. It is clear there is not much weight in the nose. (Reminds me of the mark 2 MR2 a little).
It is not a problem because the steering lets you know what is happening, but it requires concentration (or driiving slower, which is obviously not an option[])

It is hard to get the traction control to come on, especially in the dry.
Getting the car airborne does the job, as does driving over loose chippings or gravel. When airborne it seems well judged and saves the revs rising, but on chippings it seemed a little abrupt. I actually thought there was a fuel pickup problem, since I was low on fuel at the time, till I saw the light come on.

Clearly winter and snow in particular is going to be the main test.
Does the ABS work in reverse (didn' t in my last two cars)?

 

[Guest]

Jeremy Clarkson refers to it as the ' 911 method'
When I had the Porsche Driving Experience (full day with a Porsche instructor) the method was emphasised (and the results clearly dmonstrated on the skid pan - see my painful efforts at http://www.porschepictures.net/absoluteig/gallery.asp?categoryid=39):
hold the power going in and use the power coming out.

 

[Kevin Cooke]

Stuart,

In the C4S I have now done an instruction day with Don Palmer and 2 track days, Castle Combe and Goodwood, I can assure you that the C4S is not immune to the laws of phsyics, tyre design and slip angles and does indeed tighten its line when the throttle is eased whenever you are anywhere near the limit of grip, but the high levels of grip available disguise this at road speeds. Thats why I do track days.

Balancing the reduction in lock with the additional turn in as the throttle is eased to get the car into an apex is one of the most enjoyable parts of driving the car and I might one day be able to consistantly get it right rather than the odd fluke.

Regards

 

[Guest]

It would be irresponsible to try to find the limits on the road. Aside from the risk of damage, the tarmac is too variable in terms of grip levels and flatness.
I just thought I would mention what I had noticed in case it tied in with others observations.

I have some to the conclusion having had the car a couple of months, that now it is run in I need to have some sort of driving day somewhere with some space. I know Porsche do a half or whole day course, and there are various other available.

I am also contemplating taking the car on a track. I have not done one before, and am a little nervous about whether my driving is really up to it. Obviously I am competent to drive round, but what I mean is whether I can put in a respectable effort.
But it is non-competitive and I don' t really have anything to prove. Plus I have to start somewhere, so I am sure it will be fun. It is just a question of actually organising it and sorting out some insurance (since I didn' t know if I would take it on a track, I didn' t get cover with my policy).

My electric comfy seats don' t really offer enough lateral support, but I have the steering wheel to hang onto. If I like it I might see about getting a bucket seat for track days if swapping them over is easy, since I use the car every day also.

 

[Kevin Cooke]

Stuart,

Brilliant! It would be great to see another C4S on PCGB track days, there were 3 at Castle Combe and 2 at Goodwood including C4S XL.

Why not jump in at the deep end and come to Silverstone in July, 1 week after the BGP it should be as sticky as hell.

Or try the Bedford day as there is absolutely nothing to hit there apart from at 1 corner.

Every level of ability is absolutely welcome, the PCGB instructors on the day are good at getting you around the track safely.

The C4S is really quite good, clearly more grip than a 996 C2 or C4 due to bigger tyres and lower suspension and I' d say quicker than a 964RS and as quick as a 993RS assuming same level of driver competence in each.

See you soon

 

[Guest]

The C4S is really quite good, clearly more grip than a 996 C2 or C4 due to bigger tyres and lower suspension and I' d say quicker than a 964RS and as quick as a 993RS assuming same level of driver competence in each.

Hi Kevin,

Be very careful making comparisons like this. Virtually everything depends on the driver on track days. Two examples: First, at the end of the hangar straight at Silverstone a 996TT on sticky rubber was pulling only 10mph more than my 3.2 on road tyres. This doesn' t mean that my car is nearly as quick as a 996TT.

Second: The 964RS is a very, very quick track car. On the right size sticky rubber (235/255) and the right track (Oulton) you can reel in even a GT3 on sticky rubber driven by a very experienced track driver. Yet other 964RSs were easy to catch in my little car.

Comparisions from track days are very very tricky - but an enormous amount of fun [8D]

Richard

 

[Kevin Cooke]

Richard,

Agreed that' s why I mentioned ' the same level of competence from each driver' . My comments were made based on the observation of a number of PCGB track day regulars over the last 3 years firstly in comparison with my old Boxster S and now in the C4S.

Regards

 

[oldtimer]

I' ve been thinking about your posting and trying to understand the understeer when lifting off, but must be several factors at work that I dont account for.

The way I have been taught is slow in fast out, and take the speed off by braking in
a straight line before the turn, then quickly foot off brake, turn wheel, foot on accelerator the right amount (!!).Continue turn with variable accelerator, meaning you can only put more on if you take some steering off, and at exit of turn you have straight steering and the most (!) accelerator pressure.
The classic problem with entering a corner too fast and lifting off the accelerator
is that the back end rises and the rear goes ' light' so that it starts to slide round -
oversteer. This can be made worse by braking in the corner, and usually if
you have taken right foot off the accelerator and put it on the brakes while
in the turn then bingo!

What you described was not so much causing oversteer as ' removing understeer'
by applying pressure on the accelerator during the turn. This will work if the front tyres
are gripping and the car has already started to turn. The right amount of accelerator
pressure is critical, too much will provoke understeer, none/too little ought to promote oversteer as described in previous paragraph. ?However you get understeer on lift off ?

Maybe its a C4S thing , I drive a 996 C2 on 18 inch wheels and a 964RS on 17 inch wheels but well within their respective limits ( so far )

 

[Kevin Cooke]

Oldtimer,

A far my elegant explanation than mine but clearly we agree.

 

[Guest]

Oldtimer, I mentioned it because I too thought it was curious.
Normally more weight on the front equals a tighter turn in (you can brake as you turn the wheel to improve turn in) and lifting off lightens the back increasing the liklihood it will slide (since the back wheels take a tighter line). Adding power reduces the weight on the front and the nose pushes wide.

I have noticed the opposite on the public roads, round a number of bends and at some roundabouts. I admit that I do not think I am at the limit. Perhaps on smoother tarmac under more controlled conditions I can observe the true behaviour, which is why I am now keen to find somewhere with some more space. I could be that I am mistaken. I am only talking about the car moving a few inches, not lurid slides.

However, if I am right then I can only assume it has something to do with being 4 wheel drive, or the PSM braking the inside front to pull the car round when the throttle is applied. I may try switching the PSM off and see if I notice a difference.

I don' t have experience of 4 wheel drive, except on this car. I have only driven front drive hatches/saloons and rear drive coupes/saloons. I am at the moment trying to see if I can discern any difference. With 95% going to the rear most of the time, I drive it like a rear wheel drive car.

 

[Kevin Cooke]

Stuart,

I drive the same car as you but I find it difficult to recognise the traits you are describing. If it was an effect of the PSM then you would notice the PSM warning light flashing.

The point of my first mail regarding tyre slip angles and pure physics also makes it difficult for me to understand what your describing. Weight transfer has far less effect on under or oversteer than the amount of work you are asking a tyre to do based on the combination of steering lock and power applied which generates the slip angle. You can do a U turn at 10mph, try it at 100 mph. All sophisticated suspension does is keep as much of the surface area of the tyre in contact with the road as is possible in all circumstances. Remember tuck in oversteer in a Triumph.

The effect of weight tranfer during breaking and accelerating is of course important as you are loading up the tryes to enable them to work a efficiently as possible. Increasing the load progressively will always generate the most grip.

So lets get together on a track day and you can drive me around and show me what you mean and I can do ditto.

See you soon

 

[oldtimer]

OK Stuart and Kevin, I think I understand the lift-off understeer phenomenon. It is probably a feature of 4wd cars, where front wheels always have some power on when foot is on accelerator. This would make the car ' squat' at the front ie put load on the front wheels resulting in more grip for the turn. The car will feel like it is understeering/will understeer if you lift off as this effectively reduces front grip.
On rwd drive only cars, like my 996C2, accelerator pressure causes car to squat at rear and when timed right improves turn in, but lift off is more neutral, does not ' feel' like understeer.
So it is a C4 / C4S thing !

 

[Guest]

Most Porsches drive like that. That is why in racing it is difficult to maintain adequate speed around turns without understeering or oversteering. [8D]