questions re winter tires setup

[tranquility]

Ok, so I finally switched back to my summers and noticed that both my rear winter tires (BMW's suggested winter pkg of Pirelli Sottozeros/style 290 wheels) are bald; the fronts are still good. Since all 4 winter tires and wheels are the same specs, I assume that I just need to buy 2 new tire replacements and do the tire fitting/rebalance on those 2 wheels. I plan on doing the following, pls advise if it makes sense or if there is a better way. If I left anything out, pls let me know. Thx!

1. since the rear tires wear faster than the fronts, I will put the new tires on the rear come next winter;
2. when the rears get worn again but are still newer than the fronts, just leave them as-is; if the rears are worn out more than the fronts, then do a swap (objective to ensure that the newer tires are placed in the rears);
3. if I need to do a swap, it is best to do a front to back swap (i.e. front right w/ rear right), not criss-cross (e.g. front right swap w/ rear left).

I also noticed that both my bald rear tires are concave(?) in that the middle part is noticeably sunk in: what does that mean?

[nicknaz]

Post a pic? Could be overinflation

[jparnes1]

You're thoughts on tire placement are sound. If you're tires are unidirectional then of course you must rotate only front to back.
That wear issue you describe is def an inflation problem.

[BMWZ4]

Hey Tranquility, how come all 4 tires are the same spec? Aren't your tires 225's in the front and 245's in the rear? (can't recall the exact sizes now, but you get my drift hopefully).
Dave

[Crazykoh]

It's because he's talking about his winter set. Lots of people who get dedicated winters get a square set.

[tranquility]

Yup, all 4 are the same so that means not unidirectional: in that case, what is the best tire swap method, front to rear or criss-cross as I've stated in my OP?

Here is a pic of the weird 'concave' shape, not sure why as I always have PSI@36/42 (F/R). As noted, my rears are deadly bald now lol:

[SgtGigglebox]

Originally Posted by tranquility

Yup, all 4 are the same so that means not unidirectional: in that case, what is the best tire swap method, front to rear or criss-cross as I've stated in my OP?

Here is a pic of the weird 'concave' shape, not sure why as I always have PSI@36/42 (F/R). As noted, my rears are deadly bald now lol:

That's the strangest tire wear pattern I've ever seen.

You haven't been driving entirely on railroad tracks, have you?

[tranquility]

Originally Posted by SgtGigglebox

That's the strangest tire wear pattern I've ever seen.

You haven't been driving entirely on railroad tracks, have you?

Strange because it's concentrated in the middle and made a concave shape? I'm puzzled also.

No, haven't been driving on rr tracks lol.

Also, not sure if relevant, but my winter rears worn out at 31K kms/19K miles.

[HerrK]

Originally Posted by tranquility

Here is a pic of the weird 'concave' shape, not sure why as I always have PSI@36/42 (F/R). As noted, my rears are deadly bald now lol:

Wow that is weird - I wonder if that concavity has anything to do with those PSI things. I understand that BMW recently submitted a patent for an ATPS (Automated Tire Pressure System). It will soon do away with the need to use and understand tire pressure. Kinda of like the DCT is going to do away with the MT.

[tranquility]

Originally Posted by HerrK

Wow that is weird - I wonder if that concavity has anything to do with those PSI things. I understand that BMW recently submitted a patent for an ATPS (Automated Tire Pressure System). It will soon do away with the need to use and understand tire pressure. Kinda of like the DCT is going to do away with the MT.

Are you trying to make a joke?


Anyway, is having this concave thing a symptom of under or over inflation?

This is the first time I've noticed it and it's my 3rd winter use for this set.

[SgtGigglebox]

Everything that I'm seeing online points to over-inflation, still digging though.

[nicknaz]

Who has access to your car? Another possibility is dsc off shenanigans....

[tranquility]

Originally Posted by SgtGigglebox

Everything that I'm seeing online points to over-inflation, still digging though.

I'm confused because I'm always using the suggested PSIs...and this is the first time in 3 winters that I've noticed this concave. However, mind you, the rears are totally bald now, so maybe that has something to do w/ it?

Originally Posted by nicknaz

Who has access to your car? Another possibility is dsc off shenanigans....

I'm the only driver, unless some aliens are using my Z as a joyride during the wee hours. I never have DSC off and don't drive that aggressively.

[Asbjorn]

Originally Posted by tranquility

I'm the only driver, unless some aliens are using my Z as a joyride during the wee hours. I never have DSC off and don't drive that aggressively.

Did you loose alot of weight recently?

[nicknaz]

Originally Posted by tranquility

I'm confused because I'm always using the suggested PSIs...and this is the first time in 3 winters that I've noticed this concave. However, mind you, the rears are totally bald now, so maybe that has something to do w/ it?




I'm the only driver, unless some aliens are using my Z as a joyride during the wee hours. I never have DSC off and don't drive that aggressively.

It is interesting because your pressures in the rear are 2psi under the owner's manual recommendation, which are 36 psi front and 44psi rear for that size of tire

However, the wear pattern in the pic, with the center more down more than the edge is consistent with overinflation.

Since you are using the OE recommended setup, perhaps you could go to a BMW center and get them to confirm the diagnosis of overinflation and write a letter to the manufacturer explaining that their recommendation resulted in premature tire wear

[CeEl]

Wonder if you had a warm winter and your tires became over inflated due to ambient temperature?

[Mick70]

Definitely the tire looks overinflated. Maybe you checked the tire pressure in very cold weather conditions but mostly used them in high temperatures?

Additionally, BMW appears to suggest too high tire pressures as this will result in low roll resistance, high mpg and low CO2/km (as reuiqred by US and EU authorities)...

Best regards

Mick

[tranquility]

Originally Posted by Asbjorn

Did you loose alot of weight recently?

LOL, no, I'm fit and trim.

Originally Posted by nicknaz

It is interesting because your pressures in the rear are 2psi under the owner's manual recommendation, which are 36 psi front and 44psi rear for that size of tire

However, the wear pattern in the pic, with the center more down more than the edge is consistent with overinflation.

Since you are using the OE recommended setup, perhaps you could go to a BMW center and get them to confirm the diagnosis of overinflation and write a letter to the manufacturer explaining that their recommendation resulted in premature tire wear

Just to make sure we're on the same page, I'm running 17” Alloy Wheels Pirelli Winter 210 Sottozero Run-flat 225/45R17 91H. The 36/42 PSI F/R is according to the driver's side sticker, which I have also been using for my original summer OEM RFTs and now my summer Michelin PSS.

I guess 31K kms/19K miles is too soon for bald rear winter tires? What would have been a better lifespan for these?

Originally Posted by CeEl

Wonder if you had a warm winter and your tires became over inflated due to ambient temperature?

That may be a factor. Overall, it was another warm winter. Still shocked that my rears could go so bald like that.

Originally Posted by Mick70

Definitely the tire looks overinflated. Maybe you checked the tire pressure in very cold weather conditions but mostly used them in high temperatures?

Additionally, BMW appears to suggest too high tire pressures as this will result in low roll resistance, high mpg and low CO2/km (as reuiqred by US and EU authorities)...

Best regards

Mick

Ok, I'll keep in mind to try a lower PSI...but for all 4 tires or just the rears? Any suggestions on PSI #s for my winters? Keep 36/42 for my Michelins?


Another thought is I put off switching back to summers for a few weeks and have been driving in warmer temps...not sure if that would speed up the wear on the tires? Still, it's a little extreme to find the rears completely bald.

[CeEl]

Although warm weather isn't ideal for winter tires, a couple of warmer than usual days won't hurt them like that. We have winter tires on all of our cars - except the Z4 - and none look like the one in your pic.

[CeEl]

Actually, why don't you stop at a tire store and just ask them for their opinion?

[wparente]

The door sticker tire pressure recommendations only apply to run flats. If you change to another tire like Michelin PSS or whatever you are on your own when it comes to tire pressure. That doesn't mean you can't use the door sticker as a start point but it only a place to start. You either have to get a tire temp sensor and use it or you adjust the pressure relative to how the tire is wearing until you get reasonably even wear across the tire. In general manufacture recommendations are high for the reasons stated in the post above.

[tranquility]

Originally Posted by CeEl

Actually, why don't you stop at a tire store and just ask them for their opinion?

I definitely will when I go in to replace those bald tires. Just wondering if anyone could shed some light on these crazy tires lol.

Ok, so the consensus appears to try for lower PSI. If the tire was conVEX, does that mean it would be under-inflated?

I always check pressure/pump tires when the tires are at rest for a long time...not sure as a poster stated above that I may have set the 'correct' pressure during such time, but when I actually drive out it is to a warmer environment, so that causes the over-inflating?