Does all 4 tires need to match? otherwise you damage the transmission!

[Nik]

I've got three tires 255-50-19, one 275-45-19. and I have spare tire 255-55-19. so 4th one doesn't match with the rest three. I need to get same size asap right?

[ducati2242]

I dont believe it will make any difference at all . When you go round a corner one side wheel will go faster than the other as one side is travelling further.
If you have one wheel which is , lets say 10 mm , bigger then one wheel will go quicker than the other. Same thing but you dont stop going round corners.

[JCL]

Originally Posted by ducati2242

I dont believe it will make any difference at all . When you go round a corner one side wheel will go faster than the other as one side is travelling further.
If you have one wheel which is , lets say 10 mm , bigger then one wheel will go quicker than the other. Same thing but you dont stop going round corners.

It isn't a side to side problem, because the differential does handle that difference. That said, if it is too big a difference side to side, the DSC protests because it sees it as constant slip. The biggest problem is front to rear, because the transfer case ends up having to deal with the difference, and it is the transfer case that can fail as a result.

Originally Posted by BlackX54.4i

Does anyone know what are BMW's specs/adherence for matching tires? within 30% (Porsche) or 4/32nd's (Audi)?

Weasel is a BMW tech, and has previously posted here that he likes to see no more than 4 revolutions per mile difference. I would look for no more than 2% difference, not sure how that compares to the 4 revolutions per mile.

[CTSportX5]

Sounds made up.

[RickM5X3]

If you look at the OE spec tires for the X5 (and X3) with staggered wheels, you will find that the OE tires tend to have just a few revs difference between front and rear. Non-spec tires can sometimes have far greater rev differences.

So I'm guessing BMW takes efforts to seek minimal revolution differences, and revs per mile front vs. rear is a good data point when selecting tires. Tirerack.com has this info.

[JCL]

Originally Posted by CTSportX5

Sounds made up.

Which part? The DSC/ABS problems with mismatched tires, the transfer case problems with mismatched tires, the suggestion to keep it within 4 revolutions per mile, or the suggestion to keep it within 2%?

[Sundayjumper]

Originally Posted by amcink

Is this statement correct? I was told by the americas tires rep that all 4 tires need to match other wise you damage the transmission.

It depends on the car, the rep may have been slightly confused.

Early X5s will cope with a bit of a difference front/rear no problem as they have a planetary centre differential. xDrive models might be more fussy due to the clutch arrangement.

The Mazda6 that my wife used to drive started juddering like crazy when we fitted two new tyres. I took the new tyres off and fitted some part-worns of the same make/model/size as the other two on the car and it was fine again. It was a horrible car though. We only bought it because I'd driven nothing but BMWs for years and felt we should be more open minded. I won't be making that mistake again ! She now has an E46

[jst2878]

i would get the same tires or all four new ones. u dont want to strip the splines on the front diff

[ducati2242]

Originally Posted by jst2878

i would get the same tires or all four new ones. u dont want to strip the splines on the front diff

Strip the splines off the front diff . That sounds unlikely .

If I got a puncture that was irreparable and my tyres were 30% worn would I change all of them . I dont think I know any sane person that would.

[JCL]

Originally Posted by ducati2242

Strip the splines off the front diff . That sounds unlikely .

If I got a puncture that was irreparable and my tyres were 30% worn would I change all of them . I dont think I know any sane person that would.

The splines that are at risk are on the output shaft of the transfer case, where the front driveshaft connects.

If you changed one tire and then had repeat DSC problems, then yes, you would need to change all of them. If you didn't have DSC warning lights, then you could try it out, and see if the front driveshaft gave any problems.

This isn't anything to do with BMW, it is with all AWD/4WD vehicles with different tire circumferences, and the problems just show up in different failure modes.