Understeer on a Quattro Help

[mickyh7]

courty said:

During spring 2018 (beast from the east) I met a q7 in a lane.
The q7 wasn't able to slow down..the look of horror on her face when she realised 2.2 tons plus summer tyres (adding 4wd doesn't change anything)=difficult to slow down on snow.
Thankfully I was in a fwd car with winter tyres and was able to stop, select reverse and back up to a place wide enough for her to pass as the q7 kept on it's titanic course.
No, I am not exaggerating.

It sounds like you are from here!
How much time did you have to do all of these manoeuvres whilst this 2.2 Ton car was bearing down on you?
Imagine if you have had 4WD and not FWD with Winter Tyres?
You could have 'Looped the Loop' and not have needed to stop for the 'Fairer Sex' !
Just interested like!

[drmike37]

A lot of these snow crashes happen at such low speeds that it feels a bit like the Austin powers steamroller scene!

And, yes, with 4x4 and winter tyres you can do anything. Almost.

[courty]

[/quote]
It sounds like you are from here!
How much time did you have to do all of these manoeuvres whilst this 2.2 Ton car was bearing down on you?
Imagine if you have had 4WD and not FWD with Winter Tyres?
You could have 'Looped the Loop' and not have needed to stop for the 'Fairer Sex' !
Just interested like!
[/quote]

Tbf I had just entered the narrow part of the lane at about 15mph.
I had my mother in the car, and her neighbour was coming up the lane, so I was ready to stop and reverse back to the wider section. How long does it take to stop from 15mph and start backing up? I don't know..5 seconds. In all that time the neighbour in the q7 was clinging to the steering wheel and slithering on. What I do know is that if I had just stopped and not had time to reverse, we would have collided, it was a close run thing. I guess she was doing about 15mph too.
On the one hand it's the difference winter tyres make, on the other it is about expectations. She expected her 4wd, "safemobile" to be good in the snow. Obviously it set off ok, so far so good, but slowing/stopping the brute was not according to expectations.
Same with aquaplanning, I have seen a couple of big 4wd SUV Mercs stuffed into the armco on motorways in rain. The drivers feel safe in their heavy machine, but in reality, very wide, low profile tyres are prone to losing grip on wet motorways.

Edited by courty on Monday 30th November 19:30

[Wollemi]

Haltamer said:

mickyh7 said:

I'm thinking also the temperature has just dropped so my Michelins have stopped working!

This is about the only reason I consider Winter Tyres living in the south:- Below 10c Summer UHP starts going iffy; Michelins seem to do a bit better at lower temperatures but even PS4s are far past their best below ~4c. (Ask me how I know! )

Modern UHP tyres are not meant for low temperatures, especially if the road surface is damp or greasy. I found Michelin PS4S can become Quite unnerving at 8.5°
The PS4 that you have are probably a little more forgiving but really at this time of year you should consider a set of winter tyres.

[Sticks.]

Wollemi said:

Modern UHP tyres are not meant for low temperatures, especially if the road surface is damp or greasy. I found Michelin PS4S can become Quite unnerving at 8.5°
The PS4 that you have are probably a little more forgiving but really at this time of year you should consider a set of winter tyres.

I found that with the MPSS' but not with any of the sets of F1 Asy's I've had.

[RobM77]

mickyh7 said:

Ok never had a 4x4 car before.
PS4 standards all round newish.
Had understeer going a little fast into a damp greasy corner.
On a normal front wheel drive or rear wheel drive car I can deal with this but on a Quattro, what's the best course of action.
Keep going, let the electronics sort it out or come off the accelerator.
S Tronic box
I know, slow down, but this was a mistake.
Thanks

Do the same thing you would in a FWD or RWD car. Understeer between turn-in and apex is mostly a matter of balance and steering technique. Sure, the inherent balance of a 4WD car will be different, the setup often is too, and you're often lumbered with narrow front tyres due to packaging constraints, but all that doesn't mean the same tools and tricks to achieve balance and remove understeer don't work in 4WD just as they do with FWD and RWD.

[BusaMK]

I suggest reading up on Quattro and how it works; you need to give the system some power for it to work properly. It won’t help you much on corner entry. Depending on the Audi (an RS with dynamic diff especially) you’ll get some rotation if you’re very aggressive with the power after the first small amount of understeer, but you’ll obviously be grateful for some space. The best way to get Quattro working is to use it on corner exit.

[osdecar]

mickyh7 said:

....
It was only the front that went., which suprised me.
....

Seems to be common belief that the end where the engine sends its power is going to be the one that breaks grip first, and this is very far from true.

Understeer/oversteer behaviour is a consequence of centrifugal force distribution vs grip distribution. The centrifugal force distribution is a function of the mass distribution of the car, and the velocity. While the grip distribution is a function of the vertical weight on each wheel and the grip coefficient of every tyre. None of these factors are related with the power distribution, therefore you can perfectly have a FWD oversteering and RWD understeering. and also the same car doing one or the other depending on what do with the controls.

While you're driving, you cannot change the mass distribution of the car and you cannot change the grip coefficient of the tyre. However, you can still affect the velocity and the weight over each wheel.

This might sound a bit too complicated or scientific, but basically means, that you can accelerate/decelerate to transfer some weight to the front tyres or the rear tyres. And you can also move the steering wheel to ask more or less from the tyres.

But, bear in mind, this transfer of weight means that if you add more grip to the front end by lifting the throttle, you are removing grip from the rear axle at the same rate, so it's a tricky balancing act.


There are several advices already about what to do and what not to do when you get to that situation, but I thought that explaining the basics of why you have to do that it would help you much more to understand and decide what to do.

[Sammarine]

I have a saying for Audi owners. They are too fat to fight.