Powering out of overtsteer in a FWD car...

[Dizeee]

I am having an interesting debate on another forum regarding something that happened to me last week. The crux of it is that - they are stating that if you oversteer in a front wheel drive car, you should apply throttle as well as steer into the skid in order to break out of it. This goes against everything I have ben taught surrounding skids and resolutions. As far as I am concerned, no matter what drive the vehicle has, when you enter an oversteer skid you should remove the cause (de clutch or release throttle) and steer into the slide, followed by gently applying throttle when the car regains traction.

Here is my initial post, and I am interested in any replies you may have...


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Today me and my wife were down in Dorset and driving back from a funeral to the wake to Corfe Mullen and eventually to Swanage. (We drove down this morning and returned this evening). Needless to say, it has been pi$$ing it down all day, and I managed to achieve my best MPG ever today on my way down as the spray and conditions were so bad. (I am hoping this coupled with where we were going builds an idea of how I "wasn't" driving ;-) ).



http://i47.photobucket.com/albums/f155/jamesdennis556/Temporary%20Files/Diag.jpg



Anyway, at a roundabout whereby I take the 2nd exit, positioned at 2 o'clock (worth noting a regular route for us), I had scrubbed off a load of speed having reached the roundabout from a NSL DC. It was particularly wet and know the RAB has an ever so slightly degenerated surface at points around it. But in general it is your normal, concrete RAB in god condition.

Anyway, I remember slowing right down and coming off the brakes as I entered the RAB, taking a 2nd and literally start to walk it around the RAB. (Red arrows portray my intended direction). We were going in the region of 15mph, certainly no more than 20mph and it is fair to say although my memory is partial, that I may have slightly straightened the line (Blue large dots). Thats about it. There was nothing special about the circumstances at all. Start to turn in, reach the required angle and balance the car around the bend at a constant speed. Almost at the point I stop turning the wheel to the right, (green cross) the back lets go (small blue dots ). In the following 1 second these were my thought processes:

Oh, bit slippy here...

Shit, really slippy...

Into a rear wheel skid now...

Erm... still turning round.

Shit, this is a big one...

Oh dear....

And there I was facing the car that was behind me on the RAB, who laughed at me, then drove off. It was all very slow, nothing at all was hit and I was aware there was only one car far enough behind me to to worry, so all in all we werent that bothered. But I just couldnt believe it had happened.

I was in complete shock. The main reason being, I just could not fathom how this happened at all. The wife actually laughed as well, much to my amazement, as she usually can't deal with involuntary car movements. She said she felt very safe and how bizarre it was considering how slow we were going. I still to this moment don't get it at all, and made a mental note there and then that on our way back we were visiting that RAB again and inspecting it. FWIW the second my arse went light I turned in the opposite direction, and followed the usual rules.

We returned later and drove round it. It was still wet and my wife said she saw a bit of petrol on the road. I didn't see any however so I am inclined not to think that was the cause. What we did both see and feel however is alot of mud / possible horse excrament on the outer half of the point we span. It was not highly visible but you could see the surface grimed and slightly brown. The point felt slippy as I drive around it but not as slippy as oil / petrol / ice etc, more like surface debris slip.

So I am left with 2 possible reasons that I can think of:

They are:

1) Debris caused the rear wheels to break traction during the turn in / bend and prevented the rear wheels from gaining grip during the correction procedure.

OR

2) Having initiated the rear wheel skid and start to turn in, I was late or sudden on releasing the throttle during correction which "could" have inadvertently contributed the spin by way of lift off oversteer, feeding it etc.

[Harsh]

have you checked the condition of your tyres and their pressures?

my old Mk2 astra used to oversteer if you lifted off the throttle on roundabouts.
mostly for fun i might add, i used to just opposite lock and apply throttle smoothly to pull the car out of it.

personally i wouldn't be snapping the throttle open or closed in any kind of skid,

progressive on or off works much better.

it does rather sound like something was on the road though, just glad you weren't going any faster and you guys didn't have a big accident.

[Dizeee]

Tyres are all good and pumped correctlt on the rear. I have not changed then for a while however, but have changed the fronts. Some recommend swapping front tyres to the back, but I haven't done this.

[Marcellus]

Diz - when I bought the ST I was given a "Training session" on the Prodrive test track....

Which included skid pan...........basically apply power and some opposite lock......but then lift just before you get the back in line again otherwise you'll fishtail out the other way..... with practice you can dance along in a straight line...

ANother way to think of it is always keep the front wheels pointing where you want to go..

Possibly some cause of confusion is that if very high powered FWD cars this will work... but I don't think it always works with lower powered cars as they can't get enough power down!!!

[Dan H]

I've been thinking about this, and in my (not very good writing style!) opinion, I think it'll work.

I reckon if you get some power back on (wheels pointing in the right direction) you effectively drag the rear of the car along inline with the front rather than letting it do it's own thing, and it should then straighten up.

Lift off oversteer is good fun when you're expecting it, i.e. deliberately provoked. Not quite so good when, like in your situation, it catches you unaware.

I'm happy to take you out in your car to practice :D

Glad it was all at low speeds and nothing got dinked :)

[Dizeee]

I agree. I have often lifted off mid roundabout/bend and had the back end out to give Lisa a giggle but only in the dry, as I feel that in the wet there is too much scope for error.

What happened in this scenario remineded me exactly of what it feels like on ice - so much slip for so long as such a low speed...

[chevy-stu]

I've never recently driven a powerful FWD car in anger enough for it to let go, but can't imagine how the back could let go before the front in a situation like this.

Surely if there was oil or mud on the roundabout (as seems likely, by the low speeds involved) surely the car would just oversteer before the back spun round on you ?

I remember a petrol station near where I live that was on a sort of roundabout, and always has diesel or other slippery oil on one half, and due to the slide off-camber was so easy to slide the car round at ridiculously low speeds, until they resurfaced it.

[Maxx]

My first post, so please be gentle.

A few points.

* Oversteer only happens if you have less grip (for your requirement) at the rear of the car than the front.
* Your requirement for grip is not the same throughout a corner, you generally need more front end grip on turn-in, equal grip on early entry and slightly more rear grip as you get fully into the corner.
* The ratio of grip is not constant, when you accelerate it goes rearward, when you lift off it goes forward, when you brake it goes further forward still. This is irrepective of FWD/RWD/4WD.
* If, by these actions, you move grip forward, you therefore take grip away from the rear.
* Grip (traction) needs to be shared between cornering and acceleration on the driven wheels, the more you use for acceleration, the less you have available for cornering.


In the example above I am almost certain the reason for the oversteer was lifting off mid-roundabout. Moving more grip forward and taking it from the rear. It is possible to correct the oversteer with steering alone but you need to recognise the overtsteer very early and be pretty quick with the correction. In FWD or RWD you can add a little power and this will help correct the oversteer (in conjunction with the steering correction). In RWD this assumes you have not created the oversteer by excess power through the rear tyres and have created wheelspin. This works because adding a little power will move weight (grip) to the rear of the car.

If you add too much power in RWD you will create wheelspin, if you are in oversteer already this is hard to "catch" so your power application needs to be fairly mild.

In FWD, because the rear (skidding) tyres do not receive power you can add lots of power, adding weight and grip to the rear and negating oversteer. This also "pulls" the car out of oversteer. If you really get sideways you can prevent a spin by putting maximum power through the front tyres, causing them to lose traction and wheelspin thus they are skidding at the same or greater rate than the rear, so for a moment the car travels sideways, grip eventually return to the rear (as the car is gradually slowing) and the car gets pulled out of the oversteer.

If you are driving through a fairly shallow bend and hit a patch of slippy road surface the worse thing you can do is lift off the gas but this is the natural reaction of almost every driver and is the main cause of spins. If you keep your throttle foot where it is and correct with the steering you won't spin.

Sorry it's a bit of a long explantion but thought it worth doing.

Maxx

[Harsh]

Wow great post!

Maxx, thats not a bad way to start on PN!

find myself agreeing with the weight transfer reasoning, certainly in front wheel drive cars, which is why left foot braking was so prevalent in rallying back in the day in group N cars.
seeing FWD cars behave like RWD was a joy and even know i love a bit of 'car dancing' as i call it.

Maxx, tell us a bit more about yourself sir

[chilled]

Ha ha, was going to contribute my first handling post, but Maxx has pretty much hit the nail on the head:
traction circle, weight transfer and momentum.

lifting off transfers weight to the front, reducing weight and therefore grip to the rear, causing oversteer.

applying fwd throttle sends the weight to the rear, increasing rear grip. And simultaneously reduces front end grip so evens up the F/R grip balance.

Watch Tiff drifting the Focus ST and Golf GTi around Rockingham on 5th gear, it's a perfect example of how you can power out of FWD oversteer. We'll ignore that the drift is started using the handbrake :D

[Dizeee]

V well written post.

The science behind it is absolute, it's inarguable.


The RAB and spin (which I still cant quite fathom unless there was grease present / or a malleable surface of sorts) was taken at around 15mph don't forget... We (my passenger can vouch) tip toed round it as it was wet in a FWD car.

What puzzles me is not the loss of grip or even why (it was wet and I have had rear tyre issues) but, it was:

1) The instant loss of control

2) The momentum of control loss

3) The continuation of momentum/direction following loss of control which was

possibly in hindsight over corrected.



But, thats a maybe. Diesel on the road is another.

I'm the first to hold my hands up following an error, but the sheer circumstance of this was and still is an unknown factor.

If I knew what I had done wrong I may not have posted up... but, as always, always worth a second opinion :)

[Dizeee]

Just re read the above, worth adding, the slide at that speed was akin if not worse to my experience of a pre-prepared slick skid pan (which when I was on was able to control nicely :) )


Hence my suggestin of grease or surface disruption... not an excuse but a valid theory :)

[Maxx]

Dizee,

Very common reason is actually Diesel or Petrol spill. I was at the NEC one year and a lorry must have just spilt some diesel on a small roundabout, 3 or 4 cars went off/spun in quick succesion.

There is also a Youtube clip from a VLN race at the Nurburgring where a car had dumped it's power steering fluid on a corner and pretty much every car ended up in the barrier/crashing, maybe dozen cars or more, will try and find it and post the link.

Harsh,

Thanks. I posted a bit more info on the Introduce yourself thread.

Maxx

[stuart.jones]

Can't really make any suggestions on why you suffered the oversteer at that point, as we all know there are so many variables to a situation like this that even if you'd gone back round there and then you may not have had the same result.

But during an oversteer moment in a FWD car the easiest way to save it is definitely to add power, engine power level is not a factor it works on all FWD cars, quite simply when you lifted off you got engine braking trying to slow the front wheels while nothing was trying to slow the rear wheels, this meant that the rear forces looked for an outlet and as you were turning it transfered the inertia sideways and into oversteer, while putting in the clutch pedal may have stopped the oversteer occuring (no engine braking) it wouldn't help you to recover the slide, adding power means the front starts to travel faster than the rear and pulls the rear back into line, this technique is even uneffected by what surface you are on, this is a technique I regularly teach people in fwd rally cars on gravel and so far (touch wood) it has never failed to keep us out of the trees.

regards, Stu.

[ChrisC]

in regards to the previous mention the the original advice on the previous forum that you should always remove power when in a slide. My experience and understanding is that if you have a mid or rear engined car with rear wheel drive then this is exactly what not to do.

Also If you have somthing like a chaterham which may have a live axle, then you can actually use the rear ends torque steer to get you facing the way you want. Recently had a good bit of practice doing this in a kart on a frozen track, its actually very effective.

I once ended up backwards in a ditch after doing a spin because of oil on the road before a turn. The contributing factor to this was not have a limited slip diff as the it was a country road and when I under then oversteered wide the left side rear was on the mud and all the power was feed there which didnt allow me to pull out of the drift with any control and they I fish tailed into a 360 spin at which point the best plan is to apply the brake hard and let go of the wheel. Its at this point I relaised that ABS doesnt work when going backwards.

[Dizeee]

This post keeps popping up. And it is an interesting one.

To this day I keep recalling this moment, hand on heart, I was caught out, and am STILL surprised that it happened. It's the only time I had an "off" but it happened, and I can't argue with that.

I have learnt from the replies. I must admit that the idea of powering through a FWD slide at the time was something I was unaware of, in my head I kept it basic and thought along the lines of "rear end out, off power and steer". In the same amount of time as it took to think this, I was facing backwards.

Without looking to defend any error on my part, I have driven worse conditions before at higher speeed and having returned to the roundabout with Lisa seconds later (who was present throughout) we both agreed there seemed like a layer of surface oil was there. I perhaps should of scanned the road surface better at the time, I don't know.

I know I wasn't pushing as we were en route to a funeral. Just one of those things I guess.

I have thought about it since with the advice given, and putting power down. In hindsight given the slow speed we were travelling, I am not sure this would have come to mind as I would have been in the wrong gear to give any effective input to the course of the car (probably 2nd gear at v low revs).

[Roadcraft]

Hi All.

As Dizeee said, a very interesting topic, and having read most of the replies, some cracking advice given, the trouble is, Skid Control isn’t that simple, Dizeee had been taught the age old "power off and turn in" system, this is what is taught in most Police driving schools and a lot of the Skid control centers, and is what I taught before spending a week in Sweden with the Cedergens being shown the correct way of doing it, and to a degree this would normally work. the first thing is, how far to we turn in, quarter a turn or full lock, the way I always coach this is, steer with your eyes, look where you want the vehicle to go, and you will naturally with out thinking will steer the wheel so that the front wheels are pointing in that direction, this is the same for Understeer and Oversteer, this will reduce the effect of over correction, which is often when most drivers crash with oversteer, never normally on the initial skid, almost always with an over correction. Okay, what about the power, this was lets be honest the main question, well, it depends on what type of oversteer, if its a Power oversteer (traditional rear wheel drive car skid) so to much power being applied at mid corner, then defiantly the traditional power off/remove the energy sauce, but with Lift off or Roll oversteer (often the main reason a Front wheel drive car Oversteer) I would recommend steer the front wheels in the direction you want the car to go in and then Power back on, the way to think about it is, the car is a solid platform, and we have lost traction to the rear, so a good and often effective way of regaining the traction is to apply weight, so thinking about the car like a seesaw, if we add power the weight transfer will send most of the weight to the rear, pushing the rear wheels harder into the ground, allowing the tread to bite into the surface and allowing friction to play its part giving us traction back again, we can afford to lose weight from the front as the front wheels have already established the grip. The same go's for Understeer, I would always suggest Clutch in, as this will send most of the weight to the front of the seesaw, but with out the Clutch drag/Engine braking adding to the loss of traction.

Just my thought on this really interesting subject, hope it helps :thumb:.
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Ian

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