Checking - is it true that if you replace 1 or more tires that all must be within 3/32” of diameter or the sensors / drivetrain could be damaged???

IF it says it in the manual, then yes. I have had to abide by this for nearly every car ive had for the past two decades. It does make tires more expensive if you happen to damage one while they are new. Some will disagree and some dealers may even say no problem but ultimately the relationship between the diffs and speed of the tires is not consistent and that can mess with anything from traction control to abs or old school tire pressure sensors that were not in the tires. IT can apparently speed the wear of the coupling between the parts. This is more important on AWD vs part time and or 4wd.

This is actually very interesting topic. In theory that's true.
In practice... MB themselves are using different diamater wheels... only with 4Matic (in W206).
In RWD cars wheels on front and rear axle are identical. In case of 4Matic however, you get 225/45R18 in the front and 245/40R18 in the wheel. You can check the diameters - rear wheels are a bit smaller.
What is even more interesting, if you go with 19" wheels sizes are again different. 225/40R19 in the front and 255/35R19 in the rear. Actually this is closer diameter match than in case of 18".
What's the conclusion? I don't know Just pointing this out. Personally i'm trying to go "by the book" and if needed replacing tyres in pairs.

Thanks for the research! Agreed. We had 2 right side tires blow after a a vicious pothole got them both. I was uncomfortable with one side @ 5/32 and the other at 10/32, but with staggered tires, there is no choice. In 3 months, the computer has not thrown any codes. I did a good read-through in the manual and found NO instruction regarding replacing all tires if one will be 3/32 different. It’s beginning to sound like a tire industry warning…

LOL - I giggle when I see this topic. I can promise you...if you replace all four tires on an E, the fronts will wear out far faster than the rears (assuming alignment is correct). You will 100% deviate from this measurement standard. Our GLS also does it.

I have this behavior on -

• C300
• C240
• E350
• E63S
• GLS550
• GLS580

Very good point!!! Thanks for pointing this out.

FOLLOW UP - I asked the MB mechanic - his reply was a clear NO. For the C300, the 4Matic drive system is comprised of clutch units and any tire diameter difference within reason is fine. Other cars such as Audi - do not attempt it!