Knocking on full lock

[Macdaddy]

Now the dreary weather has set in, the grounds constantly wet and slippy with leaves i seem to have noticed that on full lock when manoeuvring I'm getting knocking sounds mostly in reverse and every maybe every two seconds or so.

I've always noticed the horrible almost grinding sounds on full lock in previous quattro/haldex cars in the past however don't remember the RS4 being like this before.

It has the sports diff and i'm wondering if thats at fault or perhaps a DRC type issue? Going to book it in with Audi however whats the initial thought, is this normal ?

[geoffdunk]

Is it knocking or scrubbing?

[johnnydog]

On both my B7 and B8, when reversing off my drive and turning on near full lock, I get a scrubbing / chattering from the front tyres - as if the tyres are attempting to 'skip' sideways. Ive always put it down to the width of the tyres and their profile, rather than a fault with the car. Especially as both models do the same...

[geoffdunk]

I had this on my B6 S4 and a regular refresh of front diff oil helped, its know as diff scrub. My current RS4 is doing it and it didn't do it all summer but has started now its colder and wetter, its under a year old too.

The larger the wheels the worse it gets, I have 20" wheels, my old B6 S4 had 18's

My friend's 64 plate Boxter has 21" wheels and that's even worse, that almost hops across the road when on full lock and reversing, its a known problem with them due to the extreme geometry they run, I can only assume the RS4 is similar.

[Afsimba]

^this my B7 and B8 now does it think it's worse again when tyres wear down especially crappy pirellis

[Macdaddy]

Thanks for the replies,

Yes it feels as though the wheels may be skipping across the tarmac but with a knock sound so may well be normal now the pirelli's are probably down to around 3mm.

I have the 20" wheels too so sounds like that and tyres that are almost done may be the reason.

[C2 VXT]

I had the same issue. Audi checked it out and said it was due to the circa 3mm tyre tread depth. To be honest I thought they were trying it on, but a full set of MPSS later, the noise had gone. Audi were right after all.

[RIV]

5:04 pm
I had the same issue. Audi checked it out and said it was due to the circa 3mm tyre tread depth. To be honest I thought they were trying it on, but a full set of MPSS later, the noise had gone. Audi were right after all.

Had the same happen on my B7 and the wife's A45, just down to tyre wear

[Ian_C]

They all do it. All modern cars have a positive castor angle. So as you turn the steering wheel onto full lock, you are actually raising the front ride height of the car. All four wheels are also trying to turn at different speeds on full lock. Say you are full lock left, your front right hand tyre will be turning the fastest out of all the four wheels because it is traveling the greatest distance (the outside of the four circles the tyres would draw out). However, this tyre is also running on its inside edge, so it doesn't have the grip of a tyre sitting flat on the tarmac.

Not an issue with just one axle driven. But with three-differential torsen quattro, all the wheels are engaged togother.

These many factors mean that the fronts on full lock running on their edges under / over rotate as the differentials try to keep up! Typically the front outside tyre under rotating iirc