[Nickies]

I installed Michelin PS4S at 11K. I am now at 37K. I keep them at 38F - 45R (staggered set up) and cross axle every 3.5K.

The rotation has been done today. Front are 7/32 and rear 6/32. When is it time to consider new tires on RWD?

[Sportstick]

4/32nds or 6 years due to inherent rubber compound deterioration over time.

[Nickies]

Originally Posted by Sportstick

4/32nds warrants replacement.

I may have took exceptional care of them. I was told when I bought they would not go over 20 - 25K. So, I am surprised they are still in good shape.

I believe they are doing fine because I keep them at the recommended pressure from OEM specs and my driving is mostly freeway and very conservative.

[John in VA]

Proper inflation & judicious rotating (contrary to BMW's suggestion!) can result in longer wear.

[msej449]

Quite a lot of performance tires are designed to maintain the same warm, dry braking distance down to 4mm (5/32") but will then degrade rapidly. I generally think about replacing mine somewhere between 4mm-3mm (5/32"-4/32" or 1/8") even 'though the UK legal limit is much lower. The differences often are amplified in cold/wet conditions. For an example, see below.

[morphomeman]

OP: the tire pressures that you report (38F, 45R) are higher than those recommended by BMW. Any reason for that? Are those pressures recommended by Michelin? Just curious.
In any case, you now have 26K miles on the tires, which is not far outside the window of normal use.

[Shovelman]

Originally Posted by msej449

Quite a lot of performance tires are designed to maintain the same warm, dry braking distance down to 4mm (5/32") but will then degrade rapidly. I generally think about replacing mine somewhere between 4mm-3mm (5/32"-4/32" or 1/8") even 'though the UK legal limit is much lower. The differences often are amplified in cold/wet conditions. For an example, see below.

This graph is a little misleading, it uses a standard trick to exaggerate the effect. It starts at 20. Imagine how it would look if the left axis were at 0.

Also, it may have been cherrypicked from data for a wide variety of tire types.

[jzeiler4]

Originally Posted by morphomeman

OP: the tire pressures that you report (38F, 45R) are higher than those recommended by BMW.

Those are the pressures recommended by BMW for speeds above 100 MPH.

[freakystyly]

These cars are also more prone to wear on the inside rear / outside front edges due to camber (or lack thereof). Increasing the pressure makes them wear a little more evenly at the expense of overall grip. That wouldn't be an issue on the highway though.

[Kernel Kurtz]

Originally Posted by jzeiler4

Those are the pressures recommended by BMW for speeds above 100 MPH.

Recommended pressures are also for a maximum loaded vehicle. The door stickers don't make this clear, the owners manual does a better job. If you don't normally have 4 people and luggage in your car you should adjust appropriately.

I've posted this link before, but no harm in doing so again...

https://www.motortrend.com/features/...ssure-sticker/

[msej449]

Originally Posted by Shovelman

This graph is a little misleading, it uses a standard trick to exaggerate the effect. It starts at 20. Imagine how it would look if the left axis were at 0.

Also, it may have been cherrypicked from data for a wide variety of tire types.

It is for one specific tyre tested at the UK's government test track and published in a standard certifcation report. It's not a manufacturer's publicity document. I chose it because it illustrates a particular point about performance tires, so I'm not sure whether this would be classed as 'cherrypicked'. So in this case, I wouldn't say it's a 'trick' in the graphing of the data. If you read the graph you can see what is the key point - at 4mm (5/32") this tyre stops the car in 24m (79ft) but at 2mm (3/32") the stopping distance at the same speed is 30m (98ft) - and that's on dry tarmac at (if I recall correctly) only 50mph. The graph would look exactly the same with the origin at 0ft as it does at 20ft. Chopping-off the left side doesn't change the axial values, it just eliminates space where no tire will present data.

The graph underlines that leaving the tires on from the half-worn 4mm to the entirely legal ¾-worn 2mm point adds 19 feet to the dry, warm braking distance. Which is no small addition.

You read a lot of people on this and related forums saying that they'll run their tires down to the legal minimum over the summer because in the dry and warm, the tread depth doesn't matter. People will often use the terms 'slicks' but slick track tires will have a completely different design: road tires aren't designed to be used like racing slicks. And thus as you can see, tread depth does matter, very much. In part this will be because the compound chemistry of the belts that are formed into a single tread is different, with the outer belts getting the more exotic compound mix and the inner ones something less effective. This on the assumption that for a performance tire, the owner is likely to replace it well before the legal minimum tread depth is reached, so there's no point in investing in costly compounds for the inner tread belts.

Now, this isn't always the case - some manufacturers like Michelin, pride themselves on building certain tires that give a consistent stopping distance right through to the minimum legal tread depth. But these won't be performance tires, like the one in the graph. They'll be the sort fitted to mainstream, small-engined hatchbacks and sedans.

But I do understand the annoyance around people truncating substantial parts of graphs and histograms in competitive or similar graphics in order to amplify differences beyond the significant. You get a lot of this on tire reviews where on a scoring of, say 100, the differences between the worst and best are only 10 and between the top five is only 5 or 6 points. Making you wonder how the drivers can be so sensitive to such differences and whether the ordinary driver would feel them at all. Chopping-off the first 90 points makes it look like there are bigger differences than there really are.

And as you say, for some reason, many manufacturers seem to insult the intelligence of their US customers by over-simplifying things like tire pressures, as if you can't cope with anything more than a single generalised setting, which is patronising. My door sticker happily carries multiple values for a wide variety of scenarios across summer, winter and different wheel/tire sizes:

[Kernel Kurtz]

Originally Posted by msej449

And as you say, for some reason, many manufacturers seem to insult the intelligence of their US customers by over-simplifying things like tire pressures, as if you can't cope with anything more than a single generalised setting, which is patronising. My door sticker happily carries multiple values for a wide variety of scenarios across summer, winter and different wheel/tire sizes:

That is more like it. To be fair it is not the manufacturers, the door sticker format is mandated by NHTSA (and here in Canada by DOT, though we just blindly follow the US). I run 35 psi all around on my summer 245/35s, with normally just myself in the car, so looks just about right.

[Nickies]

Originally Posted by morphomeman

OP: the tire pressures that you report (38F, 45R) are higher than those recommended by BMW. Any reason for that? Are those pressures recommended by Michelin? Just curious.
In any case, you now have 26K miles on the tires, which is not far outside the window of normal use.

For me, I am always alone driving. They are the only pressures the car handles properly in any conditions ( mostly highway mountain roads). I tried lower settings and it floats like a boat. I am the original owner, no mods. All tires wear is even. I am surprised because I was told they would be gone at 20K.

[Shovelman]

Thanks msje for the informative response.
Tom

[nazali]

Originally Posted by Sportstick

4/32nds or 6 years due to inherent rubber compound deterioration over time.

^^^ is "technically correct" I mean the 6 years for sure and so is the mm's in real world about 3mm.

Personally the lower you keep your tires the less effective they are, Tires and the most important part of your car bar none.

I used to wait till I could feel the wear sensor. But yes 3mil is bare minimum

Also if you have AWD it is sensitive to differences in tire wear both front to back and on the axels

There is a spec