JCL,

I'm talking about pressure gap between hot and ambient temperatures.... It seems that different tire have different gaps, like Michelin has 3-4 gap, VR's 2-3...
Now i'm interested in Bridgestone, how big is the gap?

I know what you are saying, but measuring a hot tire and concluding that it is now overinflated is just plain wrong. You don't know the spec for hot inflation, just cold inflation. Every tire will increase in pressure when driven.

The reason that manufacturers don't publish hot inflation pressures is that they are so variable. How high is the ambient temperature? How hard are you driving it? How far have you driven it?

And that is what you are seeing with your measurement of different tires. There is so much variation from the ambient, driving style, distance, etc, that the make of tire is just not relevant.

Yep.

And also if, Michelins pressure Gap is 3-4, so driving temperature of tire will be 35-36 psi what is much more from ambient, i would assume that there could exessive center line wear on that temperature difference.... However I dont experience it on my Diamaris. Scratching head...:dunno: Who knows, I might be wrong, just wanted to help. However some people reported that their sweet tire pressure spot is 33..35 psi, but they did not report any exessive tire wear.

JCL is right - you always go by cold pressure. Besides driving conditions, you don't know the design of the tire, including how much flex it has, the thickness of the cross section, etc...

the heat is generated by the energy losses that occur when the tire flexes. it's best to keep the tire at the cold pressure.

center wear could also be an attribute of the tire itself, whether manufacturing variation, design of the construction, use of multi-compound tread, etc...

only real way -
- get your alignment checked and within spec. To help decrease premature wear, you could try to zero your toe (or at least make it like 1/8-1/4 toe in rear)
- check your suspension links/bushings. the wheels/tires may change geometry too drastically when accelerating/braking which will cause funny tire wear
- change the type of tire: looks like you've been doing this, but tire wear (especially in center and intermediate ribs) could be contributed to the tire design/construction and the pressure footprint it lays on the ground when loaded. Some manufacturers may focus on reduced shoulder wear, which is often more pronounced (with more customer complaints) than center.

Everyone, thank you for your inputs.

Anerbe,
- Alignment have been checked and within specs per my original post. The posted numbers were actually a recheck (no actual adjustments made) when I bought these current Michelin and they were spot on from my last adjustments during the previous Pirelli purchase. As posted, toe are near zero, with a smidge toe-in.
- Suspension links/bushings would be on my list of things to check next. But I thought links/bushing would cause funny cuppings or irregular inner or outer wear?
- I guessed I would still have to try out another brand on my next set. But having to replace these tires every 20k is starting to get expensive :(

You guys have got me worried and thinking again, that maybe I should back off from 35f & 37r to 32f & r, as per BMW recommendations. Having said that, tyre wear thus far is acceptable and I believe even across the face of the tyre. This set of Yokohama Advan ST's (19") has travelled approx 17,000km (10,200miles). I am not an overly aggressive driver any more, having said that I do like to open the throttle a tad on weekend 1 hour runs up and over the mountains nearby (don't we all??).
Discussed over again and again, see these recent threads:Negative Camber and Tire pressure sweet spot

Following pics indicate the 2 centre grooves on each tyre with plenty of meat left on them.

Anybody else have close up pics of tread wear of 'x' brand tyres and at 'y' distance??

This may sound simple, but check the air with another gauge. I had a problem with another car with the air pressure. I always buy a new gauge with each car. It ended up being the brand new gauge was bad, and giving me bad readings. I replace it with a better gauge and the problem went away.

Good point, but that was the first thing that I did. Tried it with 4 different gauges...all within 1psi of one another.

I had the center wear issue in my two cars and after discussed with several tire dealers got another view on this.
With the tire profile as low as 40 or 35, you need to have extreme pressures in tires so that the tire keeps it's shape. The dealers even say that if the tire is under inflated, it causes that in speed, the centrifugal force pulls the center up and causes abnormal wear.
Yes, sounds grazy :)
But I have tried keep the pressure around manufacturer specs and that doesn't help, so why not try as tire professionls say/advice.

So, during summer I changed brand new tires in my other car and the pressure for 255/50-19 tire is 44 PSI (3.0 bar). So let's see next summer what's the result, now I have winter tires already.