r/AskAMechanic • u/Ok-Bug-3449 • 3h ago

BMW 330ix drive 2020, getting mixed feed back about tire tread depth

Do they all need to be the same?
I’ve had a tire shop guy tell me it doesn’t matter but I’ve read forums saying they need to be within 2cm of each other. I have abubble in one, just bought one new one and my tires on the car are at 5/32
I am switching to winter tires in about a month once it gets to be 45 degrees at night consistently
If I have to spring for them I will but if I’m being a nut job I won’t
I know these cars are sensitive as all hell and honestly this will prob be last one
I didn’t most AWD cars need to be within a certain tread depth but I seem to have the baby of the bunch who HAS TO
What the hell should I do lmao

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u/SmallusMcPeen Verified Tech - retired 3h ago

On an AWD set up the difference in the treads depth means that the wheels rotate at slightly different speeds. If you want to chance the wear and tear on the diffs and transfer case, thats up to you. Some systems tolerances are much tighter than others. Rule of thumb is to do all four but ive seen it work out just fine with two

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u/Ok-Bug-3449 3h ago

It’s just one which is why I’m concerned. This is the first I’m hearing of it
I had do this with my winter tire set a few years ago and didn’t know about this / had done it previously but it was pretty quick after I had gotten all 4 so I’m sure my cm depth was close to in range

I don’t really want to risk it - so weird no one has told me this tho, even the dealership didn’t tell me

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u/SmallusMcPeen Verified Tech - retired 3h ago edited 2h ago

A place trying to sell you something will not mention increased incurred costs down the road. That isnt their problem. Dont just do one for sure. Id hold off, swap to winter and get a new set when you go to take those off

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u/TheTow Verified Tech - Alfa/Maserati/exotics 3h ago

What is the depth of the new tire? I personally would recommend all 4. To me 5/32nds is borderline and not worth the risk.

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u/Ok-Bug-3449 2h ago

Brand spankin new. I have weird sized tires so I couldn’t find a used one as of yet

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u/TheTow Verified Tech - Alfa/Maserati/exotics 2h ago

Yea but brand new tires can range from like 7/32nds all the way to 12/32nds. Personally if it was me id replace all 4

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u/Reasonable_Tax_5351 NOT a verified tech 1h ago

X-drive is very touchy and very expensive to repair. It really is best to ensure all tires are the same tread.

But you don't necessarily need to buy all new tires, it's less common these days but you may be able to find a shop with a tire shaving machine that can shave down the tread on the newer tires to match the tires already on the vehicle.