Tire Pressure

[Havy]

I had several e-mail and phone conversation with Pirelli, Michelin and other tyre manufacturer as well as BMW Munich. After an odyssey of arguments forth and back and going deep into the tire world all are advising to use the recommended pressure which is stated in the door sticker. Just make sure that you check the pressure when the tires are cold.

[gjohnsen]

I have 3.0bar /43 PSI both front and rear on 21" tires. I can testify that the car runs smother with higher pressure in the tires. Tires are Michelin PS4S.

I believe the suspension is to soft in normal mode. In comfort mode its even softer. I always set the suspension to sport mode going over speed bumps. Otherwise its way to wallowy.

Why the car runs softer and smoother with higher pressure is beyond my knowledge. Maybe because of the spesial suspension setup on the F06/F12?

[Opie55]

My experience/feel is different. My car came from the factory with 20s", but the dealer swapped them for 19"s when I thought it was too harsh. But the door jamb sticker is still for the 20s, which require higher pressure. So when I go to the tire store they always over inflate the tires. I feel like I'm driving on four stones until I get home and adjust them downward.

[ezmaass]

As an update to this thread, I'll say I've now tested this theory with the RFTs in two extreme directions. Indeed, if you start inflating into the 40's (~42psi), the ride becomes harsher again, similar to when it drops too low (low 30's).

I've found that around 38 PSI up front and around 40 PSI in the rear is a sweet spot on my 19" Goodyear A/S RFTs. Don't get me wrong - they're still incredibly TERRIBLE tires, and this is but a bandaid that makes them feel slightly more acceptable.

I believe what's happening here:

- The RFT technology is designed to keep the sidewall stiff when the tire loses pressure. When the tire's pressure is low (e.g. 30 - 32 PSI), hitting a pothole allows the sidewall to flex more and eventually hits the point of NO flex. Whatever material is in the tire to keep the sidewall stiff must take the impact. If feels terrible.

- When the tire is too heavily inflated, as expected, it becomes much too firm. It doesn't necessarily feel as bad as under-inflated, but it's stiff and harsh.

In my testing/experience, the sweet spot is still roughly as stated here. Again, it's still nowhere near acceptable - the RFTs are terrible. This adjustment, however, has just helped make it a little LESS terrible in the time being.

I'm debating whether I replace them with non-RFTs. If I decide to keep the 650 long term, this will be a must. I'm just debating whether I keep the 650 or move on to something else.