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I did pitch in on other threads about this, TLDR is I am looking to get a nicer set of wheels for my G05 M50D.

Currently I have 742M on which I'm not so crazy about and I am considering changing to 747M - which will match all the cerium grey accents on the body of the car and I like them enough to switch.

However I've seen the X5M wheels 809 and 818M that look very nice and even the 785 from X7.

So main difference is the rim width and the offset when comparing just the rims. In addition to that if it's a complete set then the tire size differs between the models.

My understanding is (and please correct me if I am wrong) that the offset (ET) is how deep is the mounting interface from (outer face?/inner face?) of the rim. Which could them potentially affect the clearence that wheel/rim has inside the wheel arch (or whatever its called) depending on the width of the rim i.e. 9.5J vs 10.5J ?

On top of that another thing to consider is the tire's side wall height that can mess up xdrive and speed/odometer readings.

So if I don't go for wheels specific to my model, it would be best to get alloys only and match the tire height to one that is on the model specific set while the width would be more forgiving ?

So if X7 alloys are:
Front: 9,5J x 22" ET 32 mm
Rear: 10,5J x 22" ET 43 mm

with tire fitted on them being:
Front: 275/40 R22 107Y
Rear: 315/35 R22 111Y

They should take these size of tire which is fitted on 747M wheels that has only different offset compared to X7 wheelset?
Front: 275/35 R22 104V
Rear: 315/30 R22 107V

Or am I missing some other important value ?

[spike5150]

You can look up the specs of the tires you want to use and that will tell you their recommended rim width range.

Here is a link to an easy calculator for comparing sizes. The overall diameter consistency is what matters to xDrive (front and rear should be as close as possible). within reason you could used larger or smaller diameter, but this will mess up your speedometer accuracy.

https://tiresize.com/calculator/