Controlling A Slide In A RWD Car

[GravelBen]

Coyoteboy said:

Can i drag things in a tangential direction or should i start a new thread? My experience with RWD slides is as mentioned - release the steering and it seems to self correct to some extent, and that backing off too much or too little causes oversteer. However I now have an AWD and this seems to have a mixture of FWD and RWD characteristics (as you might expect) depending on the direction of the wind.
A couple of incidents spring to mind, one (following an ambulance with a family member in, at some pace) where it suffered understeer quite noticably (increasingly with easing off the throttle) until the throttle was planted - as the turbo spooled it seemed to drag its front end round and drive out of it, yet the second was during evasion of an accident where the rear broke away and application of the throttle held the rear out in a lovely slide but removing it snatched the back end back in a jiffy. What are the general thoughts on the control of such a car in these situations. Do they tend to behave like FWD on turn-in and RWD on exit?

I'll start a new thread if its wanted.

There was a discussion about it here:

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

And thought there was another AWD dynamics discussion somewhere on here too but can't find it just now.


Different 4wd cars can behave quite differently, what sort is yours? A good principal for most is 'when in doubt, power out'. IMO the biggest thing you have to be careful of when catching slides is getting the opposite lock off again quickly as it comes back, once they regain grip/traction they tend to fire off pretty rapidly in whatever direction the front wheels are pointing.

I often go with a lift/dab of brakes on turn-in to destabilise the car and help avoid understeer, then power through the corner making the most of the 4wd traction. The old Scandinavian flick is fun too, but the majority of the time you probably shouldn't be pushing hard enough on public roads to benefit from it.


PS this vid is a good demonstration of sliding an AWD, quite easy to see how the driver is playing with the balance of the car etc. Sounds too:

http://www.youtube.com/watch?v=7zYZ_zItA1Y

Edited by GravelBen on Wednesday 12th September 02:05

[Coyoteboy]

Its a celica GT4 - viscous 50:50 centre and torsen rear, touching on 300hp/280lbft when its not SORN'd lol. I try not to drive like I'd need to control a slide but these things happen from time to time, usually no deserted 2am roads with good visibility fortunately.

[GravelBen]

Coyoteboy said:

Its a celica GT4 - viscous 50:50 centre and torsen rear, touching on 300hp/280lbft when its not SORN'd lol. I try not to drive like I'd need to control a slide but these things happen from time to time, usually no deserted 2am roads with good visibility fortunately.

Hmmm never driven a GT4, most of my experience is in Subarus but 50:50 with rear lsd is pretty similar to most of them.

If you're really pushing on the key is setting the car up right for the corner, and generally remember that they're at their most stable under acceleration and least stable under lift-off or braking. Depending how close to the (real) limit you are understeer can usually be dealt with by a lift to tuck the nose in (or left-foot-brake if you've practised it enough), or clenching and firmly applying the pedal on the right. If you're already too fast for the corner accelerating may just increase the understeer, but if you can lift/brake to get it sideways then accelerate out once you're pointing the way you want to go you'll pull through it and look like a hero at the same time


disclaimer: the GT4 may well have a different balance to Subarus, and as yours has about double the power of my Legacy you may be able to make better use of the throttle to get around understeer than I can. (Can't really get mine sideways on sealed roads without being quite overcommitted to the corner, not so good if theres someone coming the other way so I tend to do it more on the loose stuff)

Edited by GravelBen on Wednesday 12th September 13:56

[Coyoteboy]

Hmm yeah, not sure about scooby weight distribution but the GT4 (ST185 in my case) is definitely something like 60:40 F/R and at ~1500kg (1464 measured on a weighbridge) its fairly slow and predictable in its motions when "out of shape". I'm not sure I could use throttle to get out of understeer, it does seem to just push onwards when you try that, I've never tried a left foot dab to help out, I might give it a go one day when i get to the track and pluck up the courage! The sure-footedness in the dry seems to provide a false sense of security to some extent, I could take medium sized roundabouts at the speed limit of the road, no problems, in the dry, but in the wet its definitely understeery. I think this is partially to do with the wider rear track I've given it, it turns in nice and fast but has increased understeer, but the usual solution is to add a stiffer rear ARB - in my mind this will only *reduce* rear grip, not increase overall cornering ability and is therefore pointless. Better to learn to set it up safely and correctly than try to correct using mechanical modifications?

[Coyoteboy]

Hmm yeah, not sure about scooby weight distribution but the GT4 (ST185 in my case) is definitely something like 60:40 F/R and at ~1500kg (1464 measured on a weighbridge) its fairly slow and predictable in its motions when "out of shape". I'm not sure I could use throttle to get out of understeer, it does seem to just push onwards when you try that, I've never tried a left foot dab to help out, I might give it a go one day when i get to the track and pluck up the courage! The sure-footedness in the dry seems to provide a false sense of security to some extent, I could take medium sized roundabouts at the speed limit of the road, no problems, in the dry, but in the wet its definitely understeery. I think this is partially to do with the wider rear track I've given it, it turns in nice and fast but has increased understeer, but the usual solution is to add a stiffer rear ARB - in my mind this will only *reduce* rear grip, not increase overall cornering ability and is therefore pointless. Better to learn to set it up safely and correctly than try to correct using mechanical modifications?

[chris7676]

WhoseGeneration said:

Which is why we should ALL meet up for a trackday or two.
So posters can demonstrate their various approaches.
...

The problem is on most trackday events they dont really welcome skidding, especially deliberately induced...

Lovesmedifflocks said:

I'd be up for that. I am yet to do a trackday in the mx5, i need to upgrade the brakes somewhat, they don't like fading everyday on the way home from work!
...

MX5 have normally very good brakes, must be something wrong with yours, fading on the road - they should be ok even for the track. Get them sorted rather than spending lots of money on upgrades. Regards

[Lovesmedifflocks]

Hmmm not really, I give them a solid 10-15mins caning, they don't fade straight away, they've been better than a lot of brakes I've had on previous cars. There are very few road cars that can cope with a track day, if you are pushing your late braking etc.

I'm gonna get some decent pads and change the fluid, that should sort it.

[pdd144c]

Everyone seem to be looking way too much into this, like someone said earlier the best bet is to find some wet grass and just experiment with your car until everything becomes natural. If you can control the car in those conditions everything else is easy... Once you've got the hang of it go and have some fun

[L14MNV]

Or do what this badass American cop does - http://www.youtube.com/watch?v=6tfnNaPqW2o&mod...

[Greensleeves]

Terry_Banchard said:

Hi

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.

Firstly, apologies for gatecrashing the Advanced Driver's board. I failed my IAM test three times for downchanging before junctions, bends and other hazards and (because this came instinctively and I found it bloody hard not to) never grasped the concept of arriving in far too high a gear and picking one at the last minute.

This was a goos post by Terry and, apart from the backbiting and bickering there have been some good posts about steering angles, slip angles, weight transfer, holding onto or letting go of a steering wheel, not getting in to the situation in the first place, ad infinitum.

All quite worthless in a situation where you are not travelling at 2mph (just in case there may be a diesel spillage) and find yourself knitting socks on a slippery roundabout. The fact is that there is only a certain amount of grip which you can use to alter direction or speed and if there isn't enough, you are going on the grass! End of story. Whether you go on the grass forwards, backwards or sideways, you may be able to control.

If there is enough grip, correct application of brakes, throttle and steering will allow you to use the space available, as it appeared that Terry did in his FWD.

Had he been in a rear wheel drive, to match engine speed to road speed would have neutralised the car and allowed him to steer round it. Backing off would have stepped the back end out. Accelerating would have stepped the back end out. A car that is travelling sideways will scrub speed so it's not a bad situation to be in because without touching the brakes and thus losing the steering, you are losing speed and changing direction at the same time. Things go belly up if you can't control the slide once you've started one.

There's no substitute for experience and I personally think that skid control should be part of a compulsory post pass curriculum.

(As an aside, in this situation, letting go of the steering wheel would have you on the grass irrelevant of whether there was sufficient grip to get round! )

[Lovesmedifflocks]

Hmmm that's still not true but hey, I guess being a drift instructor doesn't qualify me well enough...? Does anyone live in the North West? I'll take you out and show you how letting go of the steering wheel works, heck, try it in your own RWD car if you like! Arghhhhhh!!!!

[ten2two]

Controlling a rear wheel slide is the same as controlling any other wheel slide --- easy - remove the cause of the skid. skidding is cause by 1.braking 2.accelleration 3. steering and 4. speed. As an instructor on a nice oily skid pan I am showing drivers how to control and get out of skids nearly every day. and by the way dont let go of the wheel, one day it will go beyond centre and you won't know whats hit you.

[GreenV8S]

ten2two said:

Controlling a rear wheel slide is the same as controlling any other wheel slide --- easy - remove the cause of the skid.

That's OK at first glance, but as soon as you get into a situation where the car has built up some yaw momentum the problem gets a lot more complicated. Removing the cause is no longer enough, you now have to damp down the oscillations as well.

[advanceddriver]

ten2two said:

Controlling a rear wheel slide is the same as controlling any other wheel slide --- easy - remove the cause of the skid. skidding is cause by 1.braking 2.accelleration 3. steering and 4. speed. As an instructor on a nice oily skid pan I am showing drivers how to control and get out of skids nearly every day. and by the way dont let go of the wheel, one day it will go beyond centre and you won't know whats hit you.

On an oily skid pan everything happens in slow motion though, with no momentum effects. As GreenV8s points out once speed in involved it's quite different.

I'm not sure what you mean when you say it will go beyond centre? When the car starts to slide, if you release you grip on the wheel it will steer itself away from centre into the skid, but not too much like a panicing human will!

Any steering input is beyond centre or it's not steering?

Just to clarify this isn't letting go of the wheel completely and sitting cross armed until the slide has stopped. See the video I posted.

[ten2two]

The yaw momentum is caused by oversteering in the first intance.To be able to get out of it you need acres of tarmac which unfortunatley we don't always have. Even on a 'what you call a slow motion skid pan'tail wagging still occurs bebeause of slow reaction times and oversteering.

[GreenV8S]

ten2two said:

The yaw momentum is caused by oversteering in the first intance.

That's true, but my point is that removing the initial cause of the slide is only part of the solution. In the situation where the car has got significantly out of shape, regaining control requires damping down the yaw oscillation and there's much more to that than just removing the cause of the slide.

[Lovesmedifflocks]

This is partly what I was saying earlier, it isn't a case of correcting prolonged oversteer, but more that the car has got out of shape and consequently it will "bounce" from one way to the other. Extending the length of the initial oversteer and turning it into more of a drift gives time for the car to settle and for the driver to get things under control and correct the slide under his (or her!) own conditions.

[ph123]

We've been controlling this slide since 1st Sept ... !

[advanceddriver]

ten2two said:

The yaw momentum is caused by oversteering in the first intance.To be able to get out of it you need acres of tarmac which unfortunatley we don't always have. Even on a 'what you call a slow motion skid pan'tail wagging still occurs bebeause of slow reaction times and oversteering.

You don't need acres to oversteer a car. If you do it correctly all you need is the extra space a slightly sideways car takes up. This could be less than a metre. See every rally driver on a narrow road.

When you suddenly have far less grip than you thought. Then you need lots of space simply to wait for the speed to scrub off. See almost every rally crash!!

[Greensleeves]

Cat - pigeons, pigeons - cats.

I'll stand some flack here but what the hell is this oversteer you are talking about? Are you all incorrectly referring to the way the back end of a car steps out while the front still has grip? That's not oversteer, that's "getting the back end out!"

Oversteer is something completely different caused by incorrect or worn suspension geometry, wrongly angled springs or bump steer where the front of the car will turn more than intended by the driver. The opposite to understeer!

And don't refer to statements made by Tiffany Dell or Geremy Clarkson on Top Gear and the like because they're getting it wrong as well.

Get it right. Losing the back end is not oversteer!