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Old 01-09-2010, 04:05 PM
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Tire Pressure & Miscellaneous Thoughts – 2010 x35D

Just a post on tire pressure and some miscellaneous thoughts that I’ve been accumulating in the 6 weeks since picking up my X5. This forum has been great in helping me to understand the nuances of owning a diesel BMW.

Tire Pressure
The TPM system indicates that the tire pressures are fine, but last night I decided to check the pressures with my trusty manual gauge. I have 18 inch wheels and do not have third row seating so the recommended pressures for regular driving are 32 psi for the front and 35 psi for the rear. The X5 had been parked for a few hours in the garage.

I measured the right front tire and was surprised that the gauge read 35 psi. I thought perhaps the factory or dealer inflated tires to 35 psi front and 41 psi rear, the recommended pressure for driving over 100 mph? I proceeded to check the right rear and it also indicated 35 psi. At this point, I thought back to the BMW factory tour that I was fortunate enough to take about a month ago. From what I remember, there was one conveyor belt with mounted tires and rims leading to the production line. From a process perspective, perhaps BMW filled all 18 inch X5 tires to 35 psi to simplify the assembly process.

I then proceeded to check the left front and my gauge read 32 psi. I thought that perhaps I had a slightly leaky valve stem? When the left rear also read 32 psi, I concluded that perhaps the factory had installed two of the wheels on the incorrect hubs.

Since front and rear tire sizes are the same and the tires are not unidirectional, I guess it is not that big of a deal. I will just increase the left side pressures to 35 psi and monitor (manually of course). Somehow, I am not surprised to see that the dealer marked off the “check air pressure” box on the delivery paperwork.

Other Miscellaneous Thoughts
1) If you ever get the opportunity, take the factory tour. It’s an amazing experience and you get close enough to the welding robots to be showered with a few stray sparks. Be sure to wear closed toe shoes. When I was next to the conveyor belt that fed wheels to the production line, a set of wheels for a 10-year Edition X5 passed by. Unfortunately, there were too many BMW associates between me and the emergency exit to a make a run for it. Better yet, take the factory tour and a class at the Performance Driving Center. Greer, SC is now my vacation destination of choice.

2) I noticed that the front driveshaft is only a slightly larger diameter than the rear half shafts and much a much smaller diameter than the rear driveshaft. Given that the torque split is 40/60, I was surprised at how thin the front driveshaft is.

3) My wheels are cast with “BORBET AL, UNITED STATES” on the inside face. It appears that Borbet acquired a US wheel company back in 2008.

City of Auburn | Press Releases

4) I was surprised that even without adaptive drive and third row seating that BMW measures ride height/suspension travel at all four corners. Perhaps suspension compression is a factor in activating DSC? I have seen a post on lowering links and I suppose I’ll need a set if I lower the X5. That said, the stock suspension seems decent enough and I am a little concerned that in the aftermarket, there seems to be one spring rate for all E70s despite weight differentials between the petrol I6, diesel and V8 models.

I attached some pictures as well. I think the undersides of a BMW are as beautiful as the exterior and interior.

Picture 1 - Diesel engine on display at the Zentrum
Picture 2- Front prop shaft
Picture 3 - Rear half shaft
Picture 4 - Rear suspension
Picture 5 - Rear prop shaft and rear differential
Picture 6 - Rear suspension travel gauge
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Old 01-09-2010, 05:27 PM
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tire pressures vary all the time... especially with dropping temperatures... I think they say it drops every 10F in temp changes. With that in mind, just check it once in a while and make sure they're within a couple psi of the recommendation and don't sweat the exact numbers.
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Old 01-09-2010, 07:01 PM
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Quote:
Originally Posted by rh71 View Post
tire pressures vary all the time... especially with dropping temperatures... I think they say it drops every 10F in temp changes. With that in mind, just check it once in a while and make sure they're within a couple psi of the recommendation and don't sweat the exact numbers.

Depending on the temperature, the Sun can also make a difference -- I have seen a 2-3 PSI difference between the left and the right side, when the sun is positioned such that one side is in the Sun, and the other is shaded.
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Old 01-09-2010, 09:50 PM
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I have 19" wheels and the pressure should be 35 psi rear, 32 psi front. You should check your tire pressure when they're cold and do it every couple of weeks.

Craig
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