QuestionI run Michelin 235/50 ZR18 on a BMW 7 class. Inflation charts from the manufacturer say 51 psi Max. I want to know what is the preferred pressure. Does this mean we should run at max PSI always? I like the feel better at 40, though I lose some response, it seems to gain traction and I sometimes am OK that it gives up the racecar feel via the steering wheel. Is it safe to run at 40? I expect a little more sidewall flex, and I understand I'll get some extra wear on the outsides.
AnswerMark,
The manufacturer's chart that you referred to was the TIRE manufacturer's chart - right? And as you indicated it said the MAX inflation pressure is 51 psi. But since the tire doesn't know what vehicle it is going on, how can the max pressure be appropriate for your vehicle?
On your vehicle will be a placard that lists the original tire size and the proper pressure for that size.
My book says that BMW 7 series never came with 235/50R18's. It says that there were some versions that came with 245/50R18, which may mean the tire on your vehicle is too small. If true, then this puts you at increased risk of tire failure.
If this is true then you need to use 2 psi more than what the placard lists.
If placard lists that tire size, then you have your answer.
But if the placard lists a different size altogether, then post back with the size and pressure and I'll calculate what would be appropriate.
