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Here is information that I received from Michelin. The first response was when i was making sure the tire sizes would work for my application, and the second response was earlier this year when i was trying to figure out what went wrong from someone more technical. They are somewhat contradictory in that the first one says the RPM specs are exact, and the second one says they aren't even measurements but rather they are what the European Tire and Rim requires them to be based on their dimensions. The second point in the second response agrees with my reasoning why these tires might actually be different because of the belt package, but then wouldn't that mean that the European Tire and Rim data is worthless?
In the end I think I need to pick one of three choices:
1. 225/40R19 with 255/35R19 PSS which is what they are using on brand new xdrives from the factory.
2. 235/35R19 with 265/30R19 PSS and have them run on a hunter machine with transaver to double check before i use them.
3. 235/35R19 with 265/30R19 Continental DW which many people have had on xdrive.
Response 1:
Yes, the posted data on rev per mile on our web-page would be exact. However, each tire manufacture will have different overall diameters for the same sizes. These tolerances have to be within certain governmental guidelines.. However, the variation between manufacture tires would be very similar. We would recommend that you check with your local BMW dealer for tolerance guidelines for the BMW X-Drive.
Consumer Care Department
Certified Michelin Product Expert
Response 2:
To address some of the questions below.
1. The RPM specs listed for our tires are not actual measurements. Rather they represent the center of the ETRTO (European Tire and Rim) design window. The actual RPM measurements may deviate slightly from the center of the window, but are within the ETRTO tolerances.
2. RPM is not substantially impacted by rim width, alignment settings, tire pressure, or even wear (believe it or not). It is a function of the belt package.
3. I would recommend staying with the factory OE tire sizes.
TCAR/MKT/PCM (Product Marketing)
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