Controlling A Slide In A RWD Car

[Terry_Banchard]

Hi

This is my first post so I apologise if my knowledge of this subject is not up to other members!

Recently I had a skid in a fwd hire car. I drove onto a roundabout and the front of the car started to understeer. I reduced steering angle and backed off the throttle to bring some weight over the front of the car which then led to the back stepping out. I gently accelerated to put some weight over the rear wheels, as well as adding some corrective lock. The car then straightened up and I exited the roundabout without hitting anything. To be honest this manoeuvre, though instinctive, was more luck than judgement on my part. I subsequently found out other people had the same issue on the roundabout which I believe was due to a diesel spill. I appreciate I should not of got into this situation in the first place but I do not think I was driving very quickly for the conditions (dry, warm sunny day, good visibility etc).

What would of been the course of action if the car had been RWD? Should I have accelerated to bring some weight over the rear wheels when the rear end started to slide? I presume I should apply the accelerator to maintain the same speed and spread the car's weight over both axles - is this correct?

I have often wondered what happens if I decelerate or accelerate when the back of a rwd car steps out accidentally.

Can anyone recommend any publications or videos to assist a beginner such as myself on car control at the limit? I have bought a couple of books on race car driving (I'm not a racer btw) but I have never found anything yet that says if x happens your options are y or z for these reasons - maybe I'm over simplifying the subject? I have read a lot of differing opinions though, which cloud the subject for a numpty like me.

When funds allow I will undertake some tuition on the above. My first port of call will be a skidpan!


Thanks

Terry

[mph999]

Terry_Banchard said:

Hi

This is my first post so I apologise if my knowledge of this subject is not up to other members!

Recently I had a skid in a fwd hire car. I drove onto a roundabout and the front of the car started to understeer. I reduced steering angle and backed off the throttle to bring some weight over the front of the car which then led to the back stepping out. I gently accelerated to put some weight over the rear wheels, as well as adding some corrective lock. The car then straightened up and I exited the roundabout without hitting anything. To be honest this manoeuvre, though instinctive, was more luck than judgement on my part. I subsequently found out other people had the same issue on the roundabout which I believe was due to a diesel spill. I appreciate I should not of got into this situation in the first place but I do not think I was driving very quickly for the conditions (dry, warm sunny day, good visibility etc).

What would of been the course of action if the car had been RWD? Should I have accelerated to bring some weight over the rear wheels when the rear end started to slide? I presume I should apply the accelerator to maintain the same speed and spread the car's weight over both axles - is this correct?

I have often wondered what happens if I decelerate or accelerate when the back of a rwd car steps out accidentally.

Can anyone recommend any publications or videos to assist a beginner such as myself on car control at the limit? I have bought a couple of books on race car driving (I'm not a racer btw) but I have never found anything yet that says if x happens your options are y or z for these reasons - maybe I'm over simplifying the subject? I have read a lot of differing opinions though, which cloud the subject for a numpty like me.

When funds allow I will undertake some tuition on the above. My first port of call will be a skidpan!


Thanks

Terry

R_U_Local has a few articles around that cover these issues, have a search for them.

Diesel spill, not really your fault then, nothing you can do really in anticipation, apart from being aware that you usually find out on roundabouts.

For RWD, similar, steer into the skid and that should recover, if you add power as well, you'll "powerslide" which may take you off the road, if there is limited space. If you have abs, another option would be to stand on the brakes, and steer into the skid, the abs will allow the steering to have effect and the brakes will slow you.

I speant some of last weekend at a "emergency car control" event through ClubDriving. In the safety of Bruntingthope I was able to have a good play. Although I have FWD (Mini ) I was playing with "Lift off" oversteer, and without adding power it seemed to get the car back in a smaller space than re-aplying power.

I stand to be corrected on any of the above, and I'm sure those with much more experience will be along in a minute.

Martin

Ps. clubdriving.co.uk will be running a future Bruntingthorpe event before the end of the year.

[chris_tivver]

General rule is to remove the input that cause the skid.

So if you had been using too much throttle (for the actual conditions including the diesel spill, not what you expected) then you would back off. If it was steering input then you reduce steering angle

[WeirdNeville]

1) Remove the cause of the skid
2) Steer into the direction of the skid

This advice works for both skids induced by over-enthusiastic acceleration or braking, and provided you have enough tarmac can be used to counter skids caused by coarse steering too.

If a RWD car starts to oversteer, i.e. the rear wheels skid or slide, then you should back off of the throttle first to reduce the speed of the wheels, then to steer into the skid to point the front wheels into the direction of the vehicles motion.

You have a choice between two "correct" ways to bring a FWD car back under control should a front wheel skid begin to devolop:
1) Release the accelerator and apply full lock in the direction you wanted to turn. This results in the car bleeding off speed until the front wheels "bite" again an whips you in the direction you wanted to go, but you're a passenger until they do and you may well run out of tarmac
2) Release the accelerator, straighten the steering until the front wheels are in traction again and then turn to get around the bend. This method relys on you being able to tell when the fronts are back in traction - not easy - and then not skid again when re-applying the steering, also not easy.

The 'problem' for me with a FWD skid is that you're a passenger until the car decides to grip again. If you don't have enough tarmac then you don't have a hope. However, as you found with FWD cars the instinctive response is the one most likely to get you out of trouble rather than burying you deeper in it.

However, if it really was a diesel spill then it is quite possible that the RWD car would have behaved in the same manner as the FWD car, i.e. Front wheels lose traction and you understeer. In which case doing what you did is the way to deal with it. It's when the back wheels go through the diesel too, and you have no traction all around that it gets interesting!

Many RWD cars have a reputation for being difficult to control or even dangerous because the rear end begins to swing and spin you right round, whereas FWD cars will plough straight on in a front or driven wheels skid. I can't recommmend a skid pan day enough, because these are skills you need to practice in a safe environment and you can't really learn what to do intuitively by reading about it.

Thinking back to your suggestion of using the throttle to re-balance the car I hope you can see now that it's not the best solution. You already have the rear wheels spinning, turning faster than the tarmac and also sliding sideways which is how you know there's a skid developing. Planting the throttle will simply accelerate the wheels further, with no hope of more traction and it also won't re-distribute any weight as this only happens with the wheels in traction. All that will happen is you will encourage the slide to beyond the point of no return. I've done this once on the public road and it was no fun at all.

Incidentally, re-dressing the balance of a car is something that only really matters when you're close to the limits of traction and this occurs only in a bend (in road driving). To negotiate a steady raduis bend smoothly you need a nice constant throttle to keep the distribution of weight even and consistent. Plant the throttle in a rwd car and the weight going to the back tends to promote oversteer or skids. Plant the throttle in a FWD car and the shift of weight to the rear tends to promote understeer. Lift off oversteer occurs when you remove weight from the rear wheels by lifting off the throttle (usually abruptly) in either a RWD car or some of the livelier FWD cars, usually hot hatches which have a nose heavy distribution anyway. I've had a couple of experiences when pressing on around a bend when I've had to fight the instinct to lift off the throttle, because I've known that if I did I'd be investigating hedgerow fauna rather quickly!

Edited by WeirdNeville on Saturday 1st September 22:59

Edited by WeirdNeville on Saturday 1st September 22:59

Edited by WeirdNeville on Saturday 1st September 23:00

[WhoseGeneration]

FWD, the handbrake can be your friend but get on a skidpan to learn how.
One reason I like the IAM (Roadcraft) way of applying the handbrake in normal usage.
"Button in" becomes intuitive.

ETA.
Yup, "flyoff" handbrake makes it opposite I know.

Edited by WhoseGeneration on Saturday 1st September 23:21

[Terry_Banchard]

Hi

Thanks for everybody's comments. I will re-read R U Local's articles and I will go on a skid pan course asap.

Thanks

[turbo tim]

Welcome to PH

This thread might be of use.

[R_U_LOCAL]

Terry_Banchard said:

Hi

Thanks for everybody's comments. I will re-read R U Local's articles and I will go on a skid pan course asap.

Thanks

Try this one...

http://www.pistonheads.com/gassing/topic.asp?h=0&a...

[GreenV8S]

WeirdNeville said:

Plant the throttle in a rwd car and the weight going to the back tends to promote oversteer or skids.

That's not strictly correct, and is one of the reasons that RWD handling is so complex.

The weight transfer under acceleration tends to promote understeer. The grip 'used up' (out of the grip budget of the rear tyres) to produce this acceleration tends to promote oversteer. These two effects oppose each other. For small amounts of acceleration (relative to the available grip) the weight transfer has a greater effect and the car will tend to understeer. The effects are non-linear though and at higher levels of acceleration the car will tend to oversteer. This results in an understeer 'hump' under gentle acceleration. The size of the hump depends on the car setup but also on the level of grip available. In slippery conditions it may be almost non-existent.

This understeer hump can be used to your benefit if you're familiar with the car - gentle acceleration puts the car in the most stable attitude possible and can prevent oversteer which might have occurred on a neutral throttle. The same understeer hump can be a problem if you're trying to turn in to a corner though, and may require either backing off the power or increasing the power far enough to get out of the understeer region. This is a dangerous approach though since it relies on you having enough power available (and in grippy conditions it may take a *lot* of power) and also means that the car will be moving out of understeer towards heavy oversteer which may need quick reactions to remove the excess power.

On the other side of the coin, under engine braking the weight transfer and grip used BOTH promote oversteer, which is why engine braking is such a on powerful RWD cars.

[ph123]

IMHO the sooner on the skid pan the better.
You'll certainly have more 'driving' to do with with rwd over fwd in that sort of situation.
With rwd, you'll get the same unnerving slide at the front, and the rear slide will be bigger and very sensitve to your throttle input.
Trickey.

[Kieran]

Terry, firstly it’s great that you have decided to learn from the event, how many others would just carry on regardless. In my opinion there really is no substitute for actual experience in a controlled environment. I speak from personal and painful experience, in my very early driving career I had my first scary skid in a Peugeot 309 GTI , yes it was indeed a few years back. At that time I had just passed one of the established civilian advanced driving tests with badge proudly displayed. I could have quoted you Roadcraft verbatim back then and I must have read every book on car control theory available, if there had been a degree in under/over steer theory I would have been an honours student. However none of it prepared me in the slightest to deal with an unresponsive steering wheel, the sound of skidding tyres and a rapidly looming verge. Fortunately the only bruising was my ego but it was an invaluable lesson. I then spent the next year searching out the best coaches and facilities to put the theory into practice.

Knowledge of the ‘why’ is important however reacting appropriately in a skid ideally requires an automated response (the jargon is an unconscious competency) by regular practice. If I am in a situation where the tires are loosing traction then if I have to think about my next actions then it’s usually too late. So the best advice is invest in some decent coaching and get out there and feel it through the seat of your pants. It’s a bit like skiing or snowboarding if you’re into that, you can read the book & watch the DVD but there is no substitute for the real thing. There are a multitude of decent coaches and facilities to match your budget, my personal recommendations would be Cadence Driver Development or Don Palmer but there are many others.

All the best with the ‘research’, enjoy the learning.

Edited by Kieran on Sunday 2nd September 21:37

[advanceddriver]

In a RWD drive car you would apply the power to initiate the slide, then apply some corrective lock (initial over-correction can be avoided by letting the wheel slide though your hands and the front caster will point the wheels in about the right direction).

Once you are at the balance point you can increase speed and slip angle and then see how many laps of the roundabout you can do. Easy.

If as I suspect you prefer to stop the slide rather than enjoy it, then it depends. RWD cars can lift off oversteer (quite considerably as the engine provides a reverse torque, like gently applying just the rear brakes). So you find alot of accidents with RWD cars where the in-experienced user feels a slight slide, lifts off totaly and steers too much into the slide, leading to a larger slide the other way and an impact with some street furniture!

In that situation applying some power to weight up the rear and a little corrective lock would have been much better. Nothing beats some practice though.....find a wet field!

[Terry_Banchard]

Thanks Everybody!

I have spent the morning working hard (or googling skid pan)

Thanks

[Schnell]

advanceddriver said:

In a RWD drive car you would apply the power to initiate the slide, then apply some corrective lock (initial over-correction can be avoided by letting the wheel slide though your hands and the front caster will point the wheels in about the right direction).

Once you are at the balance point you can increase speed and slip angle and then see how many laps of the roundabout you can do. Easy.

If as I suspect you prefer to stop the slide rather than enjoy it, then it depends. RWD cars can lift off oversteer (quite considerably as the engine provides a reverse torque, like gently applying just the rear brakes). So you find alot of accidents with RWD cars where the in-experienced user feels a slight slide, lifts off totaly and steers too much into the slide, leading to a larger slide the other way and an impact with some street furniture!

In that situation applying some power to weight up the rear and a little corrective lock would have been much better. Nothing beats some practice though.....find a wet field!

I'm going to risk putting my neck on the line here in the off chance that I have mistaken you, but; Do you actually know what you're talking about, or are your eyes sore from all that time spent on the Playstation?

[Chunks]

I agree fully Kieran, it's good to know the theory, but for it to be of any use on the road it needs to be instinctive, especially the counter intuitive aspects of car control. I would echo what has been said earlier in the thread about controlling a rwd car in a slide.

I actually think that a session on a skid pan with both a rwd car and a fwd car should be included somewhere along the process of learning to drive, it appears to me to be an almost totally ignored aspect of driving, which given our climate and the number of diesel vehicles on our roads strikes me as a little absurd.

[advanceddriver]

Schnell said:

advanceddriver said:

In a RWD drive car you would apply the power to initiate the slide, then apply some corrective lock (initial over-correction can be avoided by letting the wheel slide though your hands and the front caster will point the wheels in about the right direction).

Once you are at the balance point you can increase speed and slip angle and then see how many laps of the roundabout you can do. Easy.

If as I suspect you prefer to stop the slide rather than enjoy it, then it depends. RWD cars can lift off oversteer (quite considerably as the engine provides a reverse torque, like gently applying just the rear brakes). So you find alot of accidents with RWD cars where the in-experienced user feels a slight slide, lifts off totaly and steers too much into the slide, leading to a larger slide the other way and an impact with some street furniture!

In that situation applying some power to weight up the rear and a little corrective lock would have been much better. Nothing beats some practice though.....find a wet field!

I'm going to risk putting my neck on the line here in the off chance that I have mistaken you, but; Do you actually know what you're talking about, or are your eyes sore from all that time spent on the Playstation?

I don't own a playstation but I do own a RWD car.

Which bit of my reply are you struggling with?

[Schnell]

advanceddriver said:

Schnell said:

advanceddriver said:

In a RWD drive car you would apply the power to initiate the slide, then apply some corrective lock (initial over-correction can be avoided by letting the wheel slide though your hands and the front caster will point the wheels in about the right direction).

Once you are at the balance point you can increase speed and slip angle and then see how many laps of the roundabout you can do. Easy.

If as I suspect you prefer to stop the slide rather than enjoy it, then it depends. RWD cars can lift off oversteer (quite considerably as the engine provides a reverse torque, like gently applying just the rear brakes). So you find alot of accidents with RWD cars where the in-experienced user feels a slight slide, lifts off totaly and steers too much into the slide, leading to a larger slide the other way and an impact with some street furniture!

In that situation applying some power to weight up the rear and a little corrective lock would have been much better. Nothing beats some practice though.....find a wet field!

I'm going to risk putting my neck on the line here in the off chance that I have mistaken you, but; Do you actually know what you're talking about, or are your eyes sore from all that time spent on the Playstation?

I don't own a playstation but I do own a RWD car.

Which bit of my reply are you struggling with?

All of it.

HTH

[advanceddriver]

Maybe you should become an Advanced Driver, then you would understand. Until then you might just have to accept I am more betterer.

Edited by advanceddriver on Monday 3rd September 15:48

[Schnell]

advanceddriver said:

Maybe you should become and Advanced Driver, then you would understand. Until then you might just have to accept I am better.

Maybe you need to get back to school whereby you may learn to construct a sentence properly and learn some respect at the same time? I understand the holidays are over...

[advanceddriver]

Fixed it for you