Why change tyre every 20k? That's every YEAR for typical SG mileage. Do you know that tyres that are 50% worn give better performance because the shorter/worn thread blocks flex less? I'd be glad to buy your used tyres...
Tyres can easily go 40k on SG roads. Going back to the agent will get you factory settings -- good in a way. If you are the slow poke easy going driver, the factory specs are going to give you a car that drives straight and stable at speed.
Agree with Meek that there are good alignment shops out there. Going to one outside means you can tell him what you want. I had a 3rd party alignment shop dial out some toe-in on the front wheels and reduced the rear camber of my Z4. It is so much more responsive to steering inputs now. The downside is that the car feels a little nervous at high speed. And yes, the old alignment rear toe was way off spec, causing the car to drag its rear wheels around. After the realignment, I'm getting 9.6km/l on my Z4 (N52B25), almost 1km/l improvement.
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For my F10 it was not purely an alignment issue but also a steering issue, so I left it to MA to deal with the problem since it was under warranty. I am quite anal when it comes to how my car drives, otherwise I wouldn't buy a BMW. What is a BMW when it can't drive straight? Even my old beat up Impreza and my parent's old E class that hasn't got a tyre alignment in years drives straight as an arrow -- I can go hands free for several seconds on the expressway.
The 3rd party alignment shop said it's a common/known problem with F10 and cannot be resolved by an alignment. It seems to be an electronic steering related issue, that's why MA had to reset my steering position sensor numerous times and fit shorter upper A arms to my front suspension to increase the camber on one side to counter that effect.
F series cars with electronic power steering (actually the Z4, E90 LCI and X1 LCI also has EPS) has a mechanism to return the steering to center. I am not an expert here. Maybe one day I will ask Rodney how it works, but I am guessing there should be a motor of sorts to enable active steering return. If the center point of the steering is calibrated wrong then the steering return mechanism will cause the steering wheel to return off-center, indirectly causing the car to drive to one side.
I have sold my F10 since and won't discuss that further. When I test drove my Z4 I made sure it drives straight as an arrow before I bought it and I'm frickin glad it DOES.