RS3 TC light question

[Ernst]

My first post on here (I am normally on the RS6 forum).

My wife has an RS3. Around a month ago she had the car serviced. They replaced the rear tyres and ever since the car has felt slightly twitchy and the TC light flashes regularly. For example when changing lane on a motorway at 50-70 mph or cornering at normal speeds. It does not feel right.

Anyway, our local Audi dealer has the car back now. They are claiming that the front tyres are worn and the difference in grip/circumference between the fronts and rears is the cause.

I am not convinced, especially as the fronts are (depending on who you listen to) 3.5 mm-5 mm. They will only check the geometry once the new tyres are on.

I am not convinced. I have had several RS Audi's and never had this problem.

So my question is has anyone else had a similar issue? I have told Audi they can replace the tyres but if the problem has not gone away I am not paying as the current tyres still have several months life left in them.

[Wavey Dynamicist]

The different circumference issue may be valid.. Different tyres will actually give different overall wheel diameters.. I don't know how sensetive the calibration is to these kinda things, but if your rear wheels are spinning at a significantly different speed to the fronts, the software may detect it as wheelspin.. Not good long term on these systems.

I think the easiest and most obvious thing to look at though is what brand and model are the front tyres vs the rear? If they've put on the budget of the budgets (as audi had done to the previous owner of my car) then the rear tyres may genuinely be loosing traction!

[klauster]

I would not be relying on Audi to change the tyres in the first place, take it to a reputable tyre company, have them start with the basics such as what pressures are in the front and back, I find between 37-39 seem to work best. You then need a four wheel alignment doing, its usually free to check if its out, it only costs if it needs adjustment.

[HYFR]

Wow you paid audi for tyres! There is your first mistake!

Even kwik fit are better!

I took my R8 wheel to kwik fit as had a leaking valve, they tightened it up and sorted it foc

Audi would have charged me for a brand new TPMS sensor and 2hrs labour

[Ernst]

If I had wanted to know where to source cheap tyres then the title of my thread would have been just this.

Thank you anyway for your insightful and helpful reply.

[HYFR]

You are welcome

[PetrolDave]

The TC is triggered by differences in rotational speed of the wheels as sensed by the ABS sensors, so if the front tyres are worn enough for the radius to be different enough from the rear tyres (a different make of tyre may exaggerate the difference) then it's entirely possible for the TC to be triggered.

So I wouldn't rule out the dealers explanation...

[Dave_Hedgehog]

The TC is triggered by differences in rotational speed of the wheels as sensed by the ABS sensors, so if the front tyres are worn enough for the radius to be different enough from the rear tyres (a different make of tyre may exaggerate the difference) then it's entirely possible for the TC to be triggered.

So I wouldn't rule out the dealers explanation...

Whilst i do not dispute this everything i have ever read has indicated haldex is not tyre diameter sensitive, if i remember correctly it allows up to a 5% difference (+/- 3%)

I have 7mm on my fronts and 2.5mm on my rears and have no TC light activity at all, and there is a 0.7% difference front to back before you start because of the different tyre sizes

you also no longer need new tyres all round to do the geometry you also should not pay the fortune audi will charge you to do it, look around for someone with a hunter all wheel alignment system, its much more accurate and faster than the older ways of checking a cars geo and should only cost around £75

http://www.youtube.com/watch?v=CGTHN3G_DR8

check the tyre pressures as well, i have never known an audi dealership to get them right, i have often come away with a default pressure for a normal car lol

i also dumped the conti tyres as they are terrible, MPSS's are vastly better imo

[PetrolDave]

The TC is triggered by differences in rotational speed of the wheels as sensed by the ABS sensors, so if the front tyres are worn enough for the radius to be different enough from the rear tyres (a different make of tyre may exaggerate the difference) then it's entirely possible for the TC to be triggered.

So I wouldn't rule out the dealers explanation...

Whilst i do not dispute this everything i have ever read has indicated haldex is not tyre diameter sensitive, if i remember correctly it allows up to a 5% difference (+/- 3%)

Diameter differences triggering the TC is nothing to do with Haldex, the same thing can happen on a Torsen equipped car, or even a vehicle with a Salisbury (or any other kind of) centre diff. If the ABS sensors say that the rotational speed between wheels is great enough then the TC will kick in - what I (we?) don't know is what rotational speed difference is needed for that to happen, so I (we) can't calculate what that means in terms of difference in wheel diameter. And there's always the possibility that the ABS software has an in-built factor for the normal diameter difference between front and rear wheels.

TC is a piece of complex software, and I (we) just don't have enough knowledge of the detailed parameters used in the RS3 to say whether it is or is not being triggered in this case. So it has to be a possibility, and we cannot say that the dealers explanation is wrong - because it MIGHT be right.

But it might not be...

[Dave_Hedgehog]

The TC is triggered by differences in rotational speed of the wheels as sensed by the ABS sensors, so if the front tyres are worn enough for the radius to be different enough from the rear tyres (a different make of tyre may exaggerate the difference) then it's entirely possible for the TC to be triggered.

So I wouldn't rule out the dealers explanation...

Whilst i do not dispute this everything i have ever read has indicated haldex is not tyre diameter sensitive, if i remember correctly it allows up to a 5% difference (+/- 3%)

Diameter differences triggering the TC is nothing to do with Haldex, the same thing can happen on a Torsen equipped car, or even a vehicle with a Salisbury centre diff.

hmmm sainsbury diff

[PetrolDave]

hmmm sainsbury diff

http://ollr.createaforum.com/technical- ... tep-guide/

[Dave_Hedgehog]

hmmm sainsbury diff

http://ollr.createaforum.com/technical- ... tep-guide/

lots of bits of metal and then ZZZZZZZZZZzzzzzzzzzzzzzzz

[PetrolDave]

lots of bits of metal and then ZZZZZZZZZZzzzzzzzzzzzzzzz

Some real engineering for a change, not just this software stuff

I've spent the last 2 weeks writing LabVIEW test software so it made a real change today to work on a laser powerful enough to blind you instantly - that's when engineering becomes interesting

[Dave_Hedgehog]

lots of bits of metal and then ZZZZZZZZZZzzzzzzzzzzzzzzz

Some real engineering for a change, not just this software stuff

I've spent the last 2 weeks writing LabVIEW test software so it made a real change today to work on a laser powerful enough to blind you instantly - that's when engineering becomes interesting

i actually do get the attraction of computer free mechanical cars, modern cars are just to bloody competent and to damn easy to drive, the M235i i drove recently was well setup and utterly boring, like playing a computer game, the A45 AMG is the same


what did you melt with the laser when no one was looking

[PetrolDave]

what did you melt with the laser when no one was looking

My boss might be reading this ... but there was a funny hot plastic smell