Safe Speed Forums

Today, I was turning right onto a major (in relation to mine) NSL road with very poor visibility in both directions. The road surface was pretty wet, and once I had committed I was of course monitoring traffic in case I needed to make a quick getaway.

Almost immediately after committing I saw a lorry coming up, and so floored it. This immediately caused both my rear wheels to spin, with the result that I was barely accelerating. I therefore decided to pull in to a sideroad on the left almost straight away (treating it as a layby), let the lorry past and continued on my way - no one had to do anything drastic, touch brakes, sound horns, flash lights etc. In all probability if that side road had not been there the lorry could have stopped even if I'd decided to stop in the middle of the road, it didn't seem to be going all that quickly.

While the obvious cause of this was the wheelspin, I am interested in exploring why 1) I gave such a stupid input to the accelerator in the first place, and 2) why it took me over a second to identify that my wheels were spinning.

I believe the reason for 1) is that I had my foot on the accelerator and was actively looking for conflicting traffic having already formed the plan in my mind of hard acceleration and instinctively did so (I think this is the same reason that some motorcyclists are taught never to cover the front brake).

I think the reason for 2) was simply a lack of experience in this sort of skid... I'm only used to the sideways kind and would never normally expect the car to do this, even with such a harsh input, but the combination of surface, fairly cold tyres and weather led to less grip than I was expecting. I think camber and slope were relevant too.

Is your car a puller or pusher? If a pusher you need to be much more wary of overcooking as it casn try to put you the wrong way round!

I lurve my VSA for moments like this

Pusher* (although it is a volvo 740 estate with under 140hp...)- I am pretty confident I would have corrected it by instinct if it did try to pull me the wrong way round, however straightline skid is a bit harder because it's harder (at least for me) to know it's skidding in the first place as the only signs I'm aware of are rubbish acceleration, rising revs and the sound of wheelspin. The car is an automatic as well so the revs are harder to draw conclusions from.

I'm a bit skint atm, due to being the lowly student type, but I think I will go and practice some straightline wheelspining so I can react to this quicker; I'm not sure there's much more I could have done in terms of roadcraft and avoiding traffic confict situations, but the car control was frankly shit...

*There were three major reasons I bought this car: 1) Get proper experience of a RWD car on the road 2) Get proper experience of an automatic car full stop 3) Get a very cheap to insure car. I must admit to loving it, the suspension makes it understeer heavily usually, but you can scandinavian flick it into really perverse situations. Not to mention, it's possible to fit unimaginable piles of stuff in the boot.

To expand on why I would be confident about that: I've experienced total overcooking, but I've never experienced a genuinely straightline RWD skid, apart from one or two clutch dumps in my driving life, even on a skid pan. So I wasn't able to recognise the signs very quickly. I would, however, have recognised sideways movement fairly quickly, simply due to more exposure. In this car, until today the closest I've got to straight line wheelspin are a couple of neutral dumps, but as the transmission has a reputation I haven't done more than a couple.

I doubt that both of your real wheels span because a standard differential will send all the torque to the wheel with least grip.

I agree that recognising wheelspin quickly is an experience thing.

People get very similar, although sometimes worse, effects from traction control systems these days. Having recognised the low grip, TC cuts engine power. And sometimes cuts engine power way below the level that might be expected. People say scary things like 'dead in the water'.

In a manual transmission car, I'd use wheelspin as a signal to immediately snatch second gear in such situations. When the clutch goes down as part of the gear change process the cause of the skid is removed. In second gear the torque at the wheels is probably close to halved, making further wheelspin much less likely, and making the accelerator pedal less sensitive. And, hey, you're definitely going to need second very soon anyway - this means that taking the opportunity to snatch second wastes virtually no time.

(Alternative 'standard' strategies - come off the throttle to stop the wheelspin, then squeeze again, hoping for no wheelspin this time take time too, and THEN you ALSO have to change to second.)

_________________
Paul Smith
Our scrap speed cameras petition got over 28,000 sigs
The Safe Speed campaign demands a return to intelligent road safety

although in the turning situation with the lightly loaded wheel getting all the torque.. a typical full TC system would brake that wheel to force some onto the more loaded wheel.

what you really want is an active diff (fixed and even limited slip diffs can push a (powerful) RWD into understeer under acceleration).

Because it's an auto and your first reaction was that something in the driveline was slipping or the extra revs were due to kickdown?