Tyre pressure and Knocking/rubbing noise

[Rick Hick]

I have a '21 plate c220d mag line premium night edition with 19" alloys running on Pirelli P Zero run Flats. On full lock I am getting like a rubbing/ Knocking sound like the tyre is struggling to stay on the rim. When the car was delivered the tyre pressures were set at 31psi and were showing this on the mercedes me app. I've seen on the fuel flap that the pressures should be 36psi. Firstly, should the tyre pressures be increased to what is on the fuel flap or do rum flats require lower pressures and if the pressures are wrong, could this be causing the sounds I'm hearing from the front tyre? Thanks.

 

[brandwooddixon]

Run flats don't require a lower pressure than non-run flats.
The stated MB pressures are more to do with economy than anything else, but if in doubt use them.
Run flats and higher pressures tend to give a harder ride.
Some people drop the tyre pressures for comfort, but as the tyre profile drops in size I regard higher pressures as a necessary evil both to protect the tyre and the wheel rim on bad road surfaces.
At manoeuvring speeds you may experience some tyre scrubbing on tarmac with full lock, but you shouldn't get any knocking.
I take it that the wheels and tyres are as listed in the manual.
Other than that it sounds like its a new car, so if you have any issues then the supplying dealer would be the first port of call.

 

[Rick Hick]

Thanks for your reply. I actually picked the car back up yesterday from the dealership that I bought it from and they have said that the noise it is making IS down to the run flats scrubbing, especially if its really cold. I think that this is probably why I have only just started hearing it as I bought the car in summer and we have only recently been experiencing very cold spells. I've never driven on these tyres before so it's not something I've encountered before. Appreciate the input though. thank you.