The BMW owners manual says 51 psi in the rear if 4 passengers but the max pressure on the tyre side wall issued by Bridgestone says 50 psi
The tyres are BMW specific for my car and are Bridgestone Potenza RE050A Rft.
51 psi seems very high and even though Bridgestone have made a BMW specific tyre it seems the two companies don't talk to each other and it's all pretty confusing for the end user.
Even if just 2 people in the car BMW recommended 48 psi in the rear Bridgestone.
I would imagine 1 PSI either way will make little difference, honestly. Besides, they're only supposed to be used for getting to somewhere to get a proper tyre fitted again.
Hilarious, watching people drive around on them for weeks.
Just Googled it and apparently due to the massively stiffer sidewalls on a run flat, a much higher pressure is needed to help the centre part of the tyre contact with the road.
I would go with Bridgestone figure and seems the sensible decision however I have a question.
Bridgestone recommend one figure and it's 42 psi. But this doesn't take into account the specific car it's used on.
For example the pressure in our 318d recommends 36 psi in the rear for the same tyre our 330d recommends 51 psi. I agree a few psi won't make much difference but 15 psi will. The pressures quoted are for the same 255/30zr19 Bridgestone RE050A Rft.
That does seem strange, both definitely rear pressures? It makes sense for the front as you would expect the 330 engine to be much heavier than the 318 hence the higher pressure needed but the rear??? Hang on though surely they're different size tyres which would go some way to explain?
Andy I was quoting rear pressures for both the 318d and 330d with a 255/30ZR19 so the only variable I can see is the 330d overall vehicle weight is 250kg more but 15 psi for the same tyre seems a bug difference imo.
Problem is the bigger the tyres the more they cost too!
I think most of the issue is wear at different psi s. Sadly you'll find out in a few thousand miles, but I think your right it's a very confusing set of advice.