Tyre Pressures 235/35/19

[BOWS3]

Hi all, put 8x19" on my S3 to replace 8.5x18". Gone from pzero nero on the 18s to sp sport9000. Dunlops are 235/35/19. What pressures should be in these.
The reason I'm asking is the car now feels very unstable at high speed. Only since I've changed the wheels. There's currently 45psi in them (hot).
Hope you can help.

Chris.

[johneroberts]

38 psi is about right
cheers
jr

[peterb]

No particular experience or knowledge, but 45psi sounds rather high for a relatively light car. The 255/35/19s on the RS6 are specified at 40psi (cold).

I would imagine that you're running on a fairly small contact patch.

What pressure where the original 18s running at?

If there's no solid advice from anywhere else, I would try dropping them by about 5psi, and see what it's like then.

[BOWS3]

Thanks for the info guys. The 18s used to run 36psi. I called Dunlop and they would not commit to even giving me a guide pressure. Spoke to Kim @ QST , he says he uses 36psi all round with 19s on an S3.
Think I'll probably try either 36 or 38 as john says.
I bought the wheels from Elite, and a phone call to them was very unnerving. He told me 34 F and 38 R. When I asked him where he had this info from he said they just take manufacturers reccomendations and add a couple of pounds. I asked him why they came inflated to 45psi and he said that was probably the pressure needed to push the beads out and that they expect the customer to put the correct pressures in.

Chris.