2006 Cooper R50: Oil and Tire Pressure

[rphox2003]

I bought a 2006 Mini Cooper a few weeks back and am still getting used to it. A few questions:

1. I've got standard 15" tires and thought the ride a little hard. I checked the tire pressure and found the previous owner had them at 37 psi. I lowered the tires to 32 but was wondering why he would keep them so high.
2. I noticed today that the oil pressure gauge seem to be moving up and down more than usual. When driving the gauge would move up towards 5 bars and when idling it would drop down. Is this normal?

[The Nun]

Run flat tyres use and need the high pressure, depends what youve got fitted?

[rphox2003]

All four are 175/65 R15 84H. I have a spare tire underneath the rear of the car, so I doubt they're run-flats. How can I tell?

They're definitely not the original tires as the front pair are a different make than the rear pair. I wish I would have checked that when I bought the car.

[Caveman]

The tires won't be runflats as they're not available in 15" tires.