Tire Tread Miss Matching
 

Warning, I got a split in my left rear tire and it was in the sidewall. No way to repair it, so it had to be replaced. I was advised by Discount Tires not to miss match the tire brand and tread. They said the x drive has sensors and it will make the trans go crazy trying to figure out what is needed for traction. I replaced both back tires. Now when I go around curves, corners, and sudden lane change with some speed my X3 starts fishtailing getting really squirally. It's really scary. It's because the tread in the front is different and half of the tread is worn. Now I have to replace the front tires as well. So much for trying to get off cheap. Don't try what I did, you will be sorrrry.:thumbup:

1. different tires should not be on one car, because they have different characteristics so your car will either under or oversteer especially on wet or snowy conditions. thats why its stupid to put winter tires on one axle and keep AS or summer on the other.
2. if overal diameter difference is big enough it may cause damage to AWD system and all the electronics that keep you straight will be going apeshit because they will be thinking that you're spinning out as tires rotate at different speeds and thats what ABS sensors look for.

thats why i'm buying whole new summer set b/c my rear are almost worn to the bars and front are half way there, but my rear end is whining like crazy because of few mm difference.
what i would do in your case is get new tire like your current one and shave it to have same thread depth as rest, Tire Rack can do it

The X3 is sensitive to mismatched tires. There have been multiple reports of the transfer case failing prematurely due to different tread depths and brands on different axles. Another sign is like you noted, a negative effect on handling and unneeded DSC intervention.

Tire tread mismatching
 

Is there a recommended difference in tread depth between tires on an axle or between front and back tires that you should not exceed? I have a tire I must replace due to sidewall puncture, and the other tire on the axle is the original with 46K miles.

Thanks

I would use 2% as a guideline. Translated to tread depth, if there is a difference of 50% I would replace all.

Tire Tread Miss Matching
 

Thanks for the info . So if my Pirelli Scorpion STR brand new has tread depth 10/32, you are suggesting that any tire with tread depth less than 5/32 should be replaced, correct?

I wouldn't go that far. Tires are worn out when they have 2/32" left, so 50% worn is 6/32". But if they are the original tires at 47,000 miles and it was my vehicle I would replace all of them. That is a downside of an awd vehicle.

You have just as much of a problem front/rear as you do side to side. Side to side is hard on the diff, but front/rear differences are hard on the transfer case, and that is where issues have shown up with X3s with mismatched tires.

Tire tread mismatching
 

Thanks for the info. Did you get your info from BMW? I had tried reaching BMW engineers through BMW North America. I was told only the dealers have access to the engineer resources. Following that path, the engineer source said that as long as the other three tires are above spec, there would be no negative impact on the xdrive components ( transfer case, differentials) if you add a new tire at full tread depth. However, the handling may not be as good as it wood be if all tires were closer in tread depth.

I have heard 3% from BMW, but I don't know if that was for specific models or all awd variants.

I have heard of other X3 and X5 owners having problems with 2% calculated difference, with constant warning lights as the system fought to keep wheel speed constant front/rear. With my own vehicle, I would go to 2% maximum. If I had any warning lights I would change out the rest of the tires, or get the new ones shaved down to a similar tread depth.

If by 'above spec' the engineer you heard from meant that one tire at minimum tread depth plus very little, compared to the other tires being new, would not result in potential problems, then I wouldn't believe him.

Thanks for the info. I have doubts too. You mentioned warning lights. Is it always the case that if there is a problem there will be warning lights, or can you have a situation where you get no feedback from the car and eventually suffer failure to the differential or transfer case?