It depends upon what X car you are talking about. What have you got?
The honest answer is that it depends.....
Upon what tyres you have
Upon which xDrive car you have (some are worse than others)
Upon what tread depth differences exist
Upon staggered or non-staggered
Upon your risk appetite
Upon whether or not you have a warranty with BMW
There are many instances where use of non ‘*’ marked tyres (approved by BMW) have led to transmission failures. There are also instances (though significantly fewer) where this has happened with ‘*’ marked tyres - though I suspect that may be down to manufacturing variances in materials.
Changing a full set at the same time and using ‘*’ marked tyres reduces the likelihood of a problem occurring on BMWs equipped with staggered wheel sets. It is not so important on cars equipped with ‘square’ wheel sets. Changing the set as a full set maintains balanced tread depth on all corners - but is obviously expensive.
BMW are not alone with this. VAG, Merc and others have the same concerns and their own tyre standards (Merc are ‘MO’ marked).
IMHO you should use the correct rubber as your first choice. Some tyre combinations without ‘*’ marks do work absolutely fine, others don’t and there is no definite ‘do this to avoid that’ approach that guarantees no issues. All I can offer is that on the balance of evidence on here it seems using the correct rubber is a high priority.
My X6 is under warranty even though 8 years old so I need to keep within the rules laid down as part of that. I would continue to fit the proper tyres even out of warranty. They may be more expensive (£1k a set) but the alternative in the event of a failure is much worse.
And......
