Suggested tyre pressure please?

[WelshBeauty]

I've just put on four Bridgestone's - 185/55/R15, on my 2008 series I.

Guys what would you suggest for tyre pressures, FRONT and BACK please?
Particularly for best fuel performance.

Thanks everyone.

[aphybrid]

plate inside drivers door has info?

[WelshBeauty]

plate inside drivers door has info?

Should tyre pressures be specific to the car (see inside drivers door) or specific to the tyre?

[aphybrid]

tyre size and maintenance of specific to car, plus always potential insurance implications if changed,

[Lord Voltermore]

32 psi (2.2 bar) Front   30psi (2.1 bar) rear    , specific to your car on this size of tyre . The same pressure applies regardless of tyre brand  or whether its a summer tyre or all season tyre.   

I'd say these pressures are a good compromise between fuel economy and ride comfort.   

[WelshBeauty]

32 psi (2.2 bar) Front   30psi (2.1 bar) rear    , specific to your car on this size of tyre . The same pressure applies regardless of tyre brand  or whether its a summer tyre or all season tyre.   

I'd say these pressures are a good compromise between fuel economy and ride comfort.   

Am I correct to assume slack tyres bad for fuel economy, well-pumped hard tyres good for fuel economy?

[Jazzdriver]

Some owners inflate the front tyres to 34 PSI in order to reduce the tendency of the Jazz to wear out the edges of front tyres.

[Pine]

When I had my Mk1 I would add 2psi to the recommended pressures.  Never had a problem with tyre wear or road holding.

[Lord Voltermore]

Am I correct to assume slack tyres bad for fuel economy, well-pumped hard tyres good for fuel economy?

Yes. lower pressure increases the rolling resistance  of the tyre  (like trying to roll a squishy pillow). Higher pressure can lead to a harder ride and a tendency for the tread area to get more rounded  (like a cycle tyre)  which can reduce the area in contact with the road and concentrate tread wear along the centre of the tyre.

A couple of extra psi should be ok but I wouldnt go higher.
 But bear in mind that tyres  can lose 1 - 3 psi a month due to air permeating through the rubber naturally
 (not a leak as such) so check the pressure regularly.  Also note that tyre pressures increase as the tyres warm up as you drive.  So if you drive to a filling station and put 32psi in  , they may only be at 30 psi after they have cooled down overnight.. 
Also check the accuracy of the tyre pressure gauge you use  by comparing it with another gauge (or two)
Do both measurements at the same time  so you are comparing like with like.  If you drive home first or compare them next day  tyre temperature can affect the readings -   Gauges can be inaccurate by a few psi. You might think you have 32 psi but really only  have  30 psi  , or 34 psi.

[WelshBeauty]

Am I correct to assume slack tyres bad for fuel economy, well-pumped hard tyres good for fuel economy?

Yes. lower pressure increases the rolling resistance  of the tyre  (like trying to roll a squishy pillow). Higher pressure can lead to a harder ride and a tendency for the tread area to get more rounded  (like a cycle tyre)  which can reduce the area in contact with the road and concentrate tread wear along the centre of the tyre.

A couple of extra psi should be ok but I wouldnt go higher.
 But bear in mind that tyres  can lose 1 - 3 psi a month due to air permeating through the rubber naturally
 (not a leak as such) so check the pressure regularly.  Also note that tyre pressures increase as the tyres warm up as you drive.  So if you drive to a filling station and put 32psi in  , they may only be at 30 psi after they have cooled down overnight.. 
Also check the accuracy of the tyre pressure gauge you use  by comparing it with another gauge (or two)
Do both measurements at the same time  so you are comparing like with like.  If you drive home first or compare them next day  tyre temperature can affect the readings -   Gauges can be inaccurate by a few psi. You might think you have 32 psi but really only  have  30 psi  , or 34 psi.

Very thorough answer. Thank you indeed.

[embee]

Something which surprised me was how much effect the sun can have on the pressure you measure. 
I always check pressure before a long trip, usually first thing in the morning. I use a calibrated gauge reading to 0.1psi.
One morning this summer I was late in checking them and one side of the car had been facing the morning sun. Both tyres on that side were 0.3psi higher than I had previously set them at, the side in the shade were both at the previously set value. The tyres themselves didn't really feel any warmer to the touch but obviously were.  I left them alone having realised it was due to the sun.
That was early morning,  midday sun would probably have a bigger effect.