Audi A3 quattro - Loss of grip - paulc924

Had a little incident the other day which frightened the wife but puzzled me. I turned off a main road recently and onto a country side road which had a covering of snow which had been compacted where traffic had been. From this I assumed that the road was not blocked and before setting off selected first gear with no throttle and let out the clutch because of a slight downward gradient. The intention was to let the car "walk" itself down the slope using engine braking. This is something I have done many times over the years. Imagine my horror when the car begin to pick up speed and I was losing not only grip but steering control. What was a surprise is that the engine revs (without touching the throttle) rose to over 3000 rpm as if the wheels had grip but there was no engine braking and total loss of steering. The momentum gained, and in an effort to slow the engine down I applied light braking with still no throttle and the clutch still out. I applied a little more braking and thankfully came to a stop after going into a bank of soft snow. The road have levelled out and we continued our journey after checking that there was no damage. I have never had this before and I don't want to expeience it again. This is the first car I have had with ESP and if it is the cause of my incident I don't like it. The hand book does say to turn it off in loose-surface coditions. O.K. if you remember to do it but possibly lethal if you don't. This can't be right. Regards.

Audi A3 quattro - Loss of grip - gordonbennet

That must have put the wind up both of you, sounds like the snow had compacted down to form that nasty almost black ice type surface in the wheel tracks.

I too would have expected the car to hold itself back via engine braking in those circumstances, especially with an AWD version.

Have had some peculiar experiences with electronics over the years, in my early years on transporters i drove some really worn out tackle with steeper lorry decks than you find now, and being aluminium had become polished to a lethal smoothness by thousands of wheels passing up and down them...had instances on icy decks where ABS equipped vehicles would be out of control and actually gathering speed with the brakes releasing by themselves whilst attempting to come down slowly whilst older cars without ABS had no such problems.

The common theme between my experiences and yours is really slow speed, i don't think the systems on these vehicles can cope with slow speeds and allow the brakes (maybe when in gear in your Audi) to release when they shouldn't if the system gets confused, which is probably what happened, but i too would be concerned that the engine would race away, unless it was the fact the tyres regained grip and your speed had increased to the equivalent of 3000 rpm.

Different system entirely to a proper Hill Descent Control as fitted to some too-complicated-by-half off road type 4x4's.

Hence the advice (if you have three hours to spare to read the handbook cover to cover) to switch off ASR/TC/ESP or whatever fancy name they give this trickery, the thing is when is the normal driver supposed to turn the system off.

Easy enough decision when normal TC cuts the power should it detect wheelspin when you're trying to climb a hill, different kettle of fish when its the opposite scenario and the car is careering off down a slippery slope aided and abetted it would appear by what sounds like a poor stability control system...i would have expected better froma quattro version, but no doubt the car is shod with elastic bands on huge wheels to make things much better..:-).

Well done for not panicking and bringing the drama to a safe ending, could have been somewhat different to that for any of us.

Edited by gordonbennet on 22/01/2015 at 18:47

Audi A3 quattro - Loss of grip - paulc924

Thank you for your reply GB. Wife's still a bit shaken and I still am really puzzled. I have been driving in all conditions for a long time and weighed the situation up before attempting with confidence. The car's response was totally alien and one I would not wish to repeat. The bank of snow that arrested us was at the side of the road with a steep drop of to left. It could have been much worse. Won't try anything like it again in this car. Best Regards.

Audi A3 quattro - Loss of grip - bathtub tom

>>engine revs (without touching the throttle) rose to over 3000 rpm

That would suggest to me that there had to be some throttle input.

Are you certain you didn't inadvertently press the throttle instead of the brake?

Audi A3 quattro - Loss of grip - gordonbennet

Been thinking about this one, probably all rubbish.

It's an AWD, and i expect drive to the wheels will be cut (braked) as and when the electronics decide such input is needed if the vehicle 'senses' loss of grip of one or more wheels depending on various inputs, and most times the system will be triggered when the throttle is being pressed but already at some speed, performance enhancing stability system.

My thoughts from a position of total ignorance now so bare with me

going down that slippery slope on a trailing throttle in first gear the ESP system suddenly woke up and tried to play catch up....due to loss of grip of one or possibly two wheels whilst two or more others retain grip, now the system is working backwards and gets its knickers in a twist, did it increase the revs to ''catch up'' with the one or two wheels now turning in an attempt to stabilise all four as it would be designed to do?...as i said before it's not a specific Hill Descent design and i have no doubt that never in their data inputting scenarios did they envisage this combination of trailing throttle with the system suddenly detecting speed from the odd wheel or two when the system may not have been awake due to the crawl speed.

Another theory now, if one wheel started to slip, would the differential effectively multiply the speed the ESP system thought the car was suddenly travelling at and increased the revs, could the differential effect exacerbate what happened and increase the revs more than expected just by grip dragging the engine up to speed?

Not explained that at all well, hope someone's following me...imagine you have a driven axle jacked up and unbraked, you turn one wheel and unless its in gear the other wheel turns the opposite way, did that happen to the Audi during this event, add AWD into the equation without a locking centre diff and it gets more complicated (we assume normal diffs here not limited slip), could such an event mulitply the speed the engine <would> be turning at to still be direct linked to the speed at least one of the diffs are now at?

This is only me musing aloud, does anyone have any thoughts along these lines? even if its just to confirm that i'm an idiot.

Audi A3 quattro - Loss of grip - paulc924

Edited by paulc924 on 23/01/2015 at 12:49

Audi A3 quattro - Loss of grip - paulc924

>>engine revs (without touching the throttle) rose to over 3000 rpm

That would suggest to me that there had to be some throttle input.

Are you certain you didn't inadvertently press the throttle instead of the brake?

Absolutely.

 

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