TYRE FRICTION ON OILY ROAD SURFACE 1

[harrisj]

Anyone have any numerical data for the coefficient of friction of tyres on roads contaminated by diesel spillage?

I am looking at worst-case conditions for normal road tyres with reasonable tread pattern travelling over damp roads on which diesel has been spilled recently.

I would guess somewhere around 0.25 but if anyone has real numbers it would save a lot of experimentation and/or research.

thanks - John

 

[GregLocock]

Having seen a few cars get heavily sideways on spilled diesel I'd say the true answer is less than that - normal drivers don't exceed 0.25 g yet they have trouble on diesel.

I don't think there would be much difference between worst case wet diesel and ice.



Cheers

Greg Locock

 

[evelrod]

Since we are not dealing in hard data---I survived ice rather well for years, but there was this one very nasty experience with diesel fuel/freeway onramp/motorcycle tires---I think the number could be MUCH lower. A matter of perception? Perhaps. At least in the winter you expect ice!

Rod

 

[NormPeterson]

Buried in Marks' Standard Handbook for Mechanical Engineers (7th Ed) is a quoted range between 0.06 and 0.17 "for soft, slippery roads". Marks provides no further information or description, but personal experience driving through somebody else's puddle of hot spilled engine oil at ~10 mph agrees with the middle of that range.

Norm

 

[patprimmer]

I tried to stay away from this one as I cannot add any quantifiable advice or data, but I will complete the gang of 3 re driving experience anecdotes.

In 40 years of licensed driving on public roads, of which the vast majority was in a sub tropical climate, so ice was never a factor, I have only once ever encountered a situation I know for a fact was a combination of water and diesel spillage. This resulted in my only ever crash from total loss of control of the vehicle.

The incident happened at daybreak, with a heavy dew, on a tight blind hairpin corner on a mountainside. The corner had a lot of reverse camber and the hill was steep and I was going downhill. Mid corner, my car suddenly ploughed straight ahead. At first I was surprised by the sudden and total loss of steering, despite pumping the wheel with no result, I ended up about 3/4 across the centre line before I got a steering response. Another car was coming the other way, and he was cutting the corner to the extent that he was totally on the wrong side of the road. On seeing me, he reacted by turning toward his correct side, which I mostly occupied. Luckily he didn't have time to get very far back, and we crashed passenger side front to passenger side front with about a foot or less overlap. This was enough to push a guard back onto a tyre on each car, and the tyre back onto the chassis, making them underivable, but they ended up far enough apart to allow a single line of traffic through between them.

We set up some traffic control to avoid further incidence. I was controlling the traffic going down hill, from a point where I could see where I lost control.

During this time, despite being slowed to walking pace, every car that hit the slippery spot skidded straight ahead a few foot before regaining control.

While there, an Australia Post van and a school bus came by. Both spilt some diesel fuel from their tank filler at the exact same point. I presume that they both took the same route each work day, so the spilling was a constant event.

I walked to the site of the spill, and literally slipped over as the surface was to slippery to maintain balance.

When the tow truck arrived, he said he recovered several cars from this spot most days. The side of the road was so littered with broken glass and lens plastic, that you could not see the ground through it.

Once the tow trucks and the police arrived, I noticed one small speed advisory sign which was totally hidden behind a tree branch. I asked the tow truck driver and the police why no one bought out a saw to remove the branch. I got no reply, and I suspect no action.

Bottom line re co-efficient of friction, almost zero, re Roads and Traffic Authority attitude to real road safety initiatives, almost zero, re NSW police attitude to real road safety, almost zero, re tow truck driver's attitude, the obscured sign and treacherous road surface was his main source of a lucrative income.



Regards
pat pprimmer@acay.com.au
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[NormPeterson]

Maybe this is a bit tangential, but pat's incident brings up a rather important point - that when grip gets really poor other influences such as grade, road camber, and wind exert relatively much greater effect than is normally the case. If all you have is 0.10 to work with, a 5% downgrade throws away half of it.

Norm