Wheel swap/tyres and ALL the warnings!

[sukrw]

Hi guys,

Just thought I would run this by to see if anyone has had this before.

Yesterday, rear tyres were low so had new tyres fitted and also asked the fitter to swap the rear wheels with the front wheels so the new rubber on the front (I have my reasons).

When I then came to drive the car, started it up and ALL the warnings on the dash were going mad!

Active Cruise Control UnAvailable
Hill Assist UnAvailable
Tyre Pressure Monitoring System Failed
Stability Control UnAvailable

and probably even more...

Once I started to drive, some of them went off but ACC was still not available and TPMS was flashing crazy.

After some miles, I pulled over and tried to store the pressures in the system as I thought the fitter had missed swapping the front and rear pressures over. The car said it was unable to store the pressures.

This morning I checked all 4 pressures and only 1 (front right) was 3 psi too low - I pumped it up and then was able to store the pressures in the system and no warnings being displayed.

Just wondering if anyone else has come across this when swapping front and rear tyres over?

Also, the TPMS per wheel - is this in the valve or a "unit" stuck to the wheel (inside the tyre)?

Thanks guys ...

 

[Rob2k68]

TPMS is part of the ABS system, it 'knows' the circumference of the tyre based on distance travelled/speed and rotations of the wheel. Any variance due to tyre pressures or a difference in tread depth (new or swapping) wheels will trigger a low pressure warning.

 

[RichardT]

Beat me to it!
Little things can trigger the TPMS. It's really a warning to go out and check, rather than something related directly to tyre pressures.

 

[davc]

Had this a few times with the TPMS, the tyre fitters hadn't inflated the tyres to the same pressure, or to the correct pressure for that mater. When I had my fronts done the last time there was a 10psi difference between the left and right

I generally don't trust them anyway and always check and adjust when I get home as well as the tightness of the wheel nuts after 40-50 miles.

 

[Rob2k68]

Good tip above from Dave, nuts could be too loose but also if done up with an air tool then potentially too tight such that in the event of a puncture the wrench in the tool kit doesn't have enough leverage to undo them.

Recommend torque is 120Nm I believe.

 

[steeve]

I know you probably know this already but its recommended to have new tyres on the rear.

 

[Wibbly]

I know you probably know this already but its recommended to have new tyres on the rear.

Yes, I'm told this is on the basis that you want more grip on the back than front if you have to choose. This is because for most folk, the rear of a car letting go is far more difficult to control/recover from than the front doing the same...

 

[Rob2k68]

I 'heard' so could be wrong that if you have quartro that the front and rear tread depth should be no more than 1.5mm different to one another.

Anyone know if this is true or not and if true why ?

 

[sukrw]

I know you probably know this already but its recommended to have new tyres on the rear.

Exactly, this is what I understand to be the correct way to have tyres, but the tyres ive had fitted are very grippy in the wet so I wanted those on the front so I can slide the back out easier on corners in the wet; hence my "I have my reasons" in my post

Thanks guys for the replies and how the TPMS works and can be confused. A fountain of knowledge as always. Good to be a member here.

 

[Wibbly]

so I can slide the back out easier on corners in the wet

Sorry to be a killjoy, but on public roads???

 

[SteveMcB]

There are mixed views on which axel new tyres go on on a FWD car, admittedly most recommend rear but I prefer front as well. In snow or very wet conditions I want the driving wheels to have the deepest tread and if worst does come to worst I find oversteer much easier to control than understeer.

 

[Martinbanshee]

I 'heard' so could be wrong that if you have quartro that the front and rear tread depth should be no more than 1.5mm different to one another.

Anyone know if this is true or not and if true why ?

My Mk2 S-Tronic TT developed a weird clunk noise going into 6th gear and only at 35mph, after many months of failed repairs by Audi I personally discovered that a new set of rear tyres totally cured it, Audi were as baffled as me but the noise never came back.
It was suggested that the difference between front and back tyre depth was confusing the Haldex?!

I had the V6 S-Tronic with Quattro, still my favourite car.

 

[Rob2k68]

My Mk2 S-Tronic TT developed a weird clunk noise going into 6th gear and only at 35mph, after many months of failed repairs by Audi I personally discovered that a new set of rear tyres totally cured it, Audi were as baffled as me but the noise never came back.
It was suggested that the difference between front and back tyre depth was confusing the Haldex?!

I had the V6 S-Tronic with Quattro, still my favourite car.

Thanks Martin - one to be mindful of then!

 

[Gordo77]

Thanks Martin - one to be mindful of then!

Does that also mean it's quite important to have the tyre pressures accurate as well...?

 

[Rob2k68]

Does that also mean it's quite important to have the tyre pressures accurate as well...?

From memory the sticker on the door suggests that the fronts are around 3-4psi higher than the rears. I guess not sufficient enough to mess things up ??? Probably a good rule of thumb though mate.

 

[CHEZ]

Fwd cars actually grip using the rear tyres while cornering.
That is why it is important /more important to have good rear tyres.
A traffic cop once educated me this once in my youth, while handing me a producer in the back of a VAUXHALL senator. Ooo errr
This message has been rendered into my memory ever since as I escaped points and just an advisory....

 

[SteveMcB]

If the car is properly balanced though, ie an increase of power (not speed) to combat the cornering force and prevent weight transfer, front and rear grip should be equal. Overcook it and go into a corner whilst decelerating and most of the weight is on the front outer tyre. Admittedly this will cause the rear to be light and in extreme cases can induce oversteer but this can be corrected by steering/throttle. The alternative is the front slides into understeer which personally I don't like as you're invariably heading for the verge and there's always an element of 'lap of the gods' in that scenario.
In my experience a few mm of tread depth either way makes next to no difference in normal conditions, baldish tyres are actually better in the dry, but tread makes a big difference in snow or standing water, I accept there are different thoughts on this though.
PS the 24v senators with lsd were a hoot in the wet

 

[richinsoton]

I 'heard' so could be wrong that if you have quartro that the front and rear tread depth should be no more than 1.5mm different to one another.

Anyone know if this is true or not and if true why ?

It's due to driveline windup of 4x4 systems due to the differing rolling circumferences. I believe Calibra 4x4's used to suffer with it badly. Hence why BMW always like you to use 'star rated' tyres on x-drive as not all tyres even if they are the same size on the sidewall have the same rolling circumference.

A good example of what can happen in extremus - http://www.rubicon-trail.com/4WD101/driveline-bind.html

https://en.wikipedia.org/wiki/Driveline_windup