What can cause car to oversteer at very low speed/G force

d215yq

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Was driving to work today, going straight on over a roundabout with 4 other lanes at the usual 25mph and upon exiting for the first time ever the backend lost traction...I had to correct it with oversteer and luckily didn't hit anything else. This was all at 25mph, flat road, damp (rained heavily yesterday) but no standing water, 12C so now snow/ice possible. I think it was after I braked slightly which I understand would shift weight to front but as I say, at such speed/G force I wasn't expecting to worry about such "on edge" handling nuances.

I'm not a fast driver and there was no G felt at all, and on a mountain road even in the wet I would regularly rely on more grip than this (and still be overtaken by 80% of traffic!), and indeed have done recently with no problems whatsoever. The other cars in the other lanes were at a very similar speed so it wasn't like I was doing anything silly.

I've checked tyres (4.5mm all round, under 3 yrs old, correct pressure) and shock absorbers (no excessive bounce). Is this possibly something "loose" in the rear suspension that can cause this or another factor? There was no bang/noise/anything to suggest something has broken recently.

Thanks for the replies, it's genuinely the first time I've lost control of a car except for in snow since I was 18, and first in a RWD Merc.
 

Naraic

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As above...this happened to me years ago...diesel was the culprit.
 

LostKiwi

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Heavy rain will bring oil and diesel to the surface of the road. Almost certainly related.
 

John Laidlaw

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I’m with the guys almost certainly this, might have been a spill from a tank before you got there, I had similar many years ago in my 840ci which swopped ends rapidly!
 
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d215yq

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Thanks guys, I didn't know a spill would make such a difference at normal speeds. There was also no noise whatsoever from the skidding tyres, I only knew by the direction the car was going and then it suddenly came back on traction and had to steer back quickly. Well will be more careful in the damp in future.

So is my understandign correct that whilst some "looseness" in the rear suspension may not help when handling on the edge, it won't cause the sudden loss of traction at low speed in itself. Car has always passed the MOT but has creaks from rear occasionally when dry so fair to assume bushes aren't perfect, but as I say, they have always gripped well enough before so can I rule these out as cause?
 

LostKiwi

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I would say so. Especially as a one off.

As an example of how a spill and rain can affect grip MrsLK and I were travelling through France a number of years back in our Smart Roadster. Near Le Mans we saw some motor bikes ahead. The roads were pretty clear but it was the mother of all rainstorms. The car felt fine and had for at least the previous 5 miles of roundabouts and bends. We watched the bikes on the roundabout ahead and noticed they were being very cautious so followed suit. Nothing felt out of the ordinary. Approached the next roundabout and again they were very cautious. Again nothing felt out of the ordinary but we were cautious.
On the third roundabout the bikes were again very cautious but by now I was pretty sure everything was ok so on the exit gave it a little more throttle (as I would have normally) and we instantly went 90 degrees to the road. No hesitation at all it just went totally sideways in the blink of an eye. Gathered it up (f**k knows how!) and carried on down the road (getting severe earache in the left ear!) but as with your experience its never done it since in the same unexpected way.
 

BClassChris

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Just to throw a spanner in the works were you breaking at the time of loss of traction? If so I’d also consider a warped disk that has bitten more than the rest throwing you off though oil on the road can do just as much. Try it again on another piece of road in the dry and brake hard and firm if it pulls to one side it’s a brake balance issue if it’s straight and true it’s oil in the road


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Hope you have a great day
 

rorywquin

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I would suggest there may have been some spilt diesel, petrol or oil on the road surface, or even coolant. That with water can be quite lethal. If it didn't happen anywhere else as well, I'd bank on that.

Ian.
Yep - watch videos of Nurburgring when there is fluid on the track....
 

umblecumbuz

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When I spent my first winter in Malta, with temperatures still around 20degrees (sorry!), my nearest neighbour warned me to be careful on the roads, as it had rained the previous night, but was now completely dry.

'I know how to drive,' thought I.

Going down a long very slight slope with a T-junction onto a main road at the bottom, I gently touched the brakes to begin slowing down. Nothing happened. I applied them more firmly, and realised that the wheels were locked and I wasn't slowing. I eventually stopped against the bank on the far side of the main road. Nothing damaged.

My neighbour explained that with long hot dry summers, tyre and fuel residue settles into the tarmac, and the colder(!) weather brings ice-like conditions after the first rains.
 

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