StratfordShark

Up till now I've adhered to the pressures on sticker inside fuel filler cap - 2.5 bar front, 3.0 bar rear.

Just been reading through the tech specs book for my year provided by Andrew Olson for download. In the tech specs it confirms that 16 inch tires should be inflated as per the filler cap sticker. But it says that 17 inch should be 2.5 bar (36 psi) all round.

Now a PO of my S4 replaced the original wheels with 17inch Cup wheels. He bought the Porsche wheels with RDK sensors, and I know the system is pretty sensitive.

So are the tech specs correct that I should have 36psi all round? With that pressure at rear I'm pretty sure it will trip the RDK (which was set for the original 16 inch wheels), so seems like if I am to run correct pressures I'll have to disable the RDK which is a shame, as it's a useful system.

Anyone here have an RDK-equipped car which has also changed to 17 inch wheels? Any other comments on this Catch 22?

Thanks

Jim M.

PET does list two different sensors both 2.5 and 3.0 bar, so at minimum, I think you would need to replace the sensors in the rear wheels to the 2.5 bar units. Also I believe the brackets that mount the pickup's are different for 16" vs 17" wheels (couldn't find the brackets in PET). The added 1/2" space may prevent the unit from reading the pressure anyway. Is your system operational? Have you ever gotten a low pressure warning with the 17" wheels or does it just test normally when you first start the car?

To verify I would lower the pressure in one of the tires beyond what the limits are and make sure you get a digital dash warning that the tire is low.

WallyP

I would expect the 17" wheels to have the correct 2.5 bar sensors.

StratfordShark

The RDK system is fully operational.

That's interesting about different sensors, and Wally's point that the 17 inch rears should have 2.5 bar sensors. I'd assumed it was some kind of programming in RDK system which determined the trip pressures, rather than characteristic of sensor itself.

Used to get warnings from front offside when I had slow leak which has been fixed (bead sealing).

Come to think of it, I've only had a rear warning when the tire lost a lot of pressure after picking up a nail!

The PO (I've owned for just over a year) left some handwritten notes in the driver's manual, to the effect that the front sensors would give warning at 2.35 Bar, and the rears at 2.85 Bar. I'm not certain if he made these notes for the old 16 inch or new 17 inch wheels, or if the notes were made by the PO who fitted the 17 inchers, or the next owner who sold car to me!

So I need to reduce rears to 2.5, and see what the system makes of that.

Thanks for advice.

StratfordShark

Wally was correct. The rear sensors have correct 2.5 bar threshold. Must have worn tyres a bit running them at 3.0 bar!