[MarkH13]

Had a particularly scary moment over the weekend... Joining a motorway from the slip road, I saw a gap and tried to accelerate into it from about 40mph.

I was in Drive/Sport mode, and didn't floor the accelerator, but the back end snapped out right, and then left, before coming back into line

Conditions were very wet, but I thought I'd allowed for that with limited throttle input, and in the (obviously misguided) idea that Traction Control would prevent such a loss of control.

My question is, shouldn't TCS cut power before such a loss of control - or am I expecting too much from it? Or is it possible that there is a fault with it?

Many thanks.

[Sasquartch]

Traction control is reactive, it can't possibly know in advance if a wheel is going to spin up.

Possibly there was diesel or something else on the road and combined with rain meant the conditions were particularly slippery

The fact it came back into line probably indicates the traction and stability systems are working just fine :-)

[Wills2]

The DSC can only react, although depending on the inputs from various sensors it's ready to react and in certain circumstances it will intervene if it thinks things are going to go wrong (by monitoring yaw/steering angle and throttle position)

However I've had situations where the grip just disappears (oil/ice) and there really isn't a lot that the car can do to stop the initial slide.

[Tengocity]

Originally Posted by Sasquartch

The fact it came back into line probably indicates the traction and stability systems are working just fine :-)

Don't be saying that, it's always the driver who saves it! That's what I tell myself every time anyway.

[MarkH13]

Originally Posted by Tengocity

Don't be saying that, it's always the driver who saves it! That's what I tell myself every time anyway.

That's exactly what I said too, but fully aware that it probably was nothing to do with me!

[MarkH13]

Originally Posted by Sasquartch

Traction control is reactive, it can't possibly know in advance if a wheel is going to spin up.

Possibly there was diesel or something else on the road and combined with rain meant the conditions were particularly slippery

The fact it came back into line probably indicates the traction and stability systems are working just fine :-)

I'd never really thought about it, but I assumed that the sensors would pick up wheel-spin quickly (in thousandths of a second), and cut power instantly... Obviously not!

[James-335dx]

I think in Sport it is dialled back a bit to let you have a little more fun round the bendy bits. Then it steps in if it thinks you've gotten too cocky.

[Techno 9000]

Originally Posted by MarkH13

Had a particularly scary moment ....tried to accelerate from about 40mph.

I was in Drive/Sport mode, and didn't floor the accelerator, but the back end snapped out right, and then left, before coming back into line

Conditions were very wet......

Two queries
Did you hit standing water, even on one side?
How much tread depth do you have?

I'm thinking aquaplaning could have caused a large loss of traction.

[Londoner]

Suspect the answer lies in your description "very wet" conditions. The B58 is a monster with our RWD setup, got to be so careful applying power on anything other than dry roads.

[Watsey]

I've had a couple of proper tank-slappers; 45 degrees left then 45 degrees right. It does lift the pulse rate somewhat when you're about to t-bone a Merc in the inside lane one second, and then heading straight for the armco the next second !

My suspicion was that there was diesel on the road at the exit of a roundabout on a dual carriageway.

[PX3]

Out of curiosity, what tyres are you running with?

[Alscoob]

Originally Posted by Londoner

Suspect the answer lies in your description "very wet" conditions. The B58 is a monster with our RWD setup, got to be so careful applying power on anything other than dry roads.

Agreed ^^

5 ways roundabout heading north on the A11, exit roundabout, car straight accelerate briskly on the uphill section... it'll spin the rears a lot even in a very slightly moist road. So in the extreme wet... be careful..

[bishbosh]

Can depend on many things, RFT winter tyres at a couple degrees on a cold wet day for example are not the best for getting the power down. Compared to warmed up summers on a dry road.

I've had my car's back end out on one or two occasions.

[MarkH13]

Originally Posted by Techno 9000

Two queries
Did you hit standing water, even on one side?
How much tread depth do you have?

I'm thinking aquaplaning could have caused a large loss of traction.

Good tread all round, but it was wet, so aqua planing is definitely a possibility...

The other factor is that I was on an uphill gradient, which would have made traction worse (less downward force on the tyres, more force required to accelerate the car!)

[MarkH13]

Originally Posted by Londoner

Suspect the answer lies in your description "very wet" conditions. The B58 is a monster with our RWD setup, got to be so careful applying power on anything other than dry roads.

Indeed!

Although I played around with it yesterday in very wet conditions, and traction was surprisingly good... I guess there's a lot of factors come into play, and you never know how bad it's going to be until you lose it!

[MarkH13]

Originally Posted by bishbosh

Can depend on many things, RFT winter tyres at a couple degrees on a cold wet day for example are not the best for getting the power down. Compared to warmed up summers on a dry road.

I've had my car's back end out on one or two occasions.

Makes sense - I'm running standard Bridgestone RFTs, which aren't renowned for their grip, and it was cold...

The other factor, as I mentioned above, is that I was on an upward incline, which would have reduced traction further.

[MarkH13]

Originally Posted by PX3

Out of curiosity, what tyres are you running with?

Bridgestone RFTs... I'm sure that didn't help!

[RobUK]

Originally Posted by Alscoob

Agreed ^^

5 ways roundabout heading north on the A11, exit roundabout, car straight accelerate briskly on the uphill section... it'll spin the rears a lot even in a very slightly moist road. So in the extreme wet... be careful..

Hear hear. In the wet I'm always mindful of the fact it doesn't take much for the B58 to get bored and decide to be lary, much to the amusement of people around you in low torque/skinny tyre'd cars. Diesel on the road is also a consideration because in the wet it's downright lethal and difficult to spot.

[PX3]

Originally Posted by MarkH13

Bridgestone RFTs... I'm sure that didn't help!

When I first purchased my 420d (so not even a 4.0i) it had around 3k miles on the clock and one day my rear end kicked out when I was changing lanes in a 40 zone. It scared the life out of me as I wasn't expecting it during such a simple lane change! The same route I have been doing for years.
Yes there could have been something on the road, but since then I have absolutely no faith in the Bridgestone S001 RF tyres. They are such a skittish tyre any way, so if they can't handle minor imperfections in the road, then how can we trust them in the wet!

[Alscoob]

Originally Posted by RobUK

Diesel on the road is also a consideration because in the wet it's downright lethal and difficult to spot.

You can't smell it in a car either but you can do if you're on a bike, but it's a nasty bugger in either case!

[Wills2]

Always best to go one gear up in the wet to lessen the effects of torque especially when you've effectively got one wheel drive with an open differential and hard RFT.

I always used to try and go sooner and one gear higher in the wet on slip roads in the F80 M3 but that car felt awful in the wet truly awful.

[PX3]

Originally Posted by Wills2

Always best to go one gear up in the wet to lessen the effects of torque especially when you've effectively got one wheel drive with an open differential and hard RFT.

I always used to try and go sooner and one gear higher in the wet on slip roads in the F80 M3 but that car felt awful in the wet truly awful.

So change to Eco Pro mode and we should be ok.