[gIzzE]

I don't know what you mean by oversized?

But yeah, had 20" wheels on the X5, 730d and the 5GT.

All wore in funny ways until I got them off run flats.


When running run flats to get wear as close as you have means you are pretty close to having the pressures right imho.
There is however, no way I would run that car with a lower pressure on the back than the front.

The 5GT used to get through rear tyres every 5-6k miles on run flats, once on proper tyres it did 14k miles before it was traded and still had around 3-4mm across the tyre. The cords came through on the inside on that car while there was 6mm in the middle and 7mm on the outside edge. Scary stuff.

[Tjalle]

gIzzE.

X3/X4 28i has much "smaller" tires - sorry, tyres- than my rear - so, relatively speaking mine are oversized. I don`t know the load capacities, but I believe my rears can take about 50% more than STD 28i tyres.

It is possibel that Run Flats will screw things - but I don`t think so. I will go according to Plan and see if I can get about even wear - I will know in two years.

Again - wear is not too bad or uneven. Camber is OK.

I believe that weight distribution is about 55% on front - then I can go lower on rears.
Anyway, I have some experience in handling evaluation and will rethink if encountering any problems.

[gIzzE]

Originally Posted by Tjalle

It is possibel that Run Flats will screw things - but I don`t think so. I will go according to Plan and see if I can get about even wear - I will know in two years.

Well, this topic has gone on ad infinitum for the last 12-13 years since BMW started with run flats.

Putting a lower pressure in the rear can make the back end a little twitchy, it just doesn't feel as planted. My 19s on the X3 felt like that when I got the all season P-Zeros put on, knew straight away it was too low pressure at the back, they had 32psi all round, upped the rear to 36psi and it felt like it should again.


I think your wear rate is good for run flats, and I think if you lower the pressures to 2.4 rear you will end up with some serious inner edge wear on them.

The problem with run flats is, if you go too low you end up running them on the very inside egde, as Peter posted earlier, this is the result of running on too low pressure on run flats...




We ran the 5GT on the lowish allowed pressure to try and help the ride, and that is exactly what happened to ours.

[Tjalle]

Thanks for warning.

I will proceed as planned, but be very observant.

I will report experience as of next fall- now is the time for some fun driving on ice

[pokerface]

Tjalle, get an alignment done.

I pulled off my 20"s (PZero RFT) yesterday and saw no uneven wear after two summers lowered.

In the interim you may be able to mitigate wear by mounting the left side tire to the rear side wheel to wear the other side of the tire.

[Tjalle]

pokerface, I saw no scary uneven wear on three tires - but on RR.

Thanks for tip, but I believe I have control of wear - will proceed as outlined above.
I can see no indication of "bad" camber. Uneven wear on RR I blame to too high tire pressure and Swedish secondary roads leaning to the right.

I would be very interested in your measurements of remaining thread after two seasons. Mileage?

Cost for 275/35-20" P Zero RFT is anything from SEK 3.000-4.000 (US$ 350-450).

[HighlandPete]

Originally Posted by Tjalle

Law of physics.

As seen by measurements, rear middle thread depths are less than outers=riding on central part= too high pressure.
I often drive vehicle with light load.

Front middle thread depth higher than outers= too low pressure.

Have you ever had oversized superwide 20" rear tyres?

You mention "superwide" what do you mean? Much wider sections than OEM?

Don't forget the wider the section, you may be amplifying centrifugal growth, that can wear the middle, even at low pressures.

I still see you have to increase the pressure to help eliminate shoulder wear.

HighlandPete

[Tjalle]

Pete: OEM tires for e.g. 28i is much "smaller" - same weight in rear. I estimate load capacity on my 20" 275/35 being about 50% higher. I - normally -drive with very light load in rear.

Unfortunately, living in Sweden, I can- legally - rarely go faster that 70-80 mph - there should be very limited centrifugal force at that speed. I believe pressure is main reason for somewhat higher wear in the middle on rears.

I will increase pressure in front tyres.

Only "excessive" shoulder wear in rear is RR outer - not inner. LR shoulders are "pefect".

Thanks for all interest and constructive input. I will proceed one year according to my plan, but if problem, I will go back and see if I might have neglected good advice.

[Polo08816]

Originally Posted by Tjalle

Lotus: No INFO on Tire Rack - nor Pirelli - homepages.

Obviously there is no problem with camber. I.e BMW has done its homework - camber does not change with loaded vehicle - so does not track= good stability/grip even on bumpy roads.

I have done further analysis: rears will last for total three years and front five.
I can moderate wear with my other car - and the throttle
This is better than expected for front and worse for rear- I can live with that.

I will reduce pressure rear to 2.3 and increase front to 2.9. 2.3 is a bit tricky - less room for bad roads- but since I can monitor pressure with TPMS - no sweat. Add pressure in rear if heavily loaded.

Wintertires will go with: 2.8 front and 2.4 rear except for when skiing (heavily loaded), when 2.8 also rear.

I don't know about the X3 specifically, but how the vehicle is loaded definitely affects the camber especially for a MacPherson strut suspension. I did this experiment this past Friday with my 2014 335i M Sport RWD. I took the alignment readings with the vehicle loaded (~500lbs) according to BMW prep instructions and then un-loaded the vehicle after I we had the alignment spot on for another reading.

http://f30.bimmerpost.com/forums/sho....php?t=1033446

[Tjalle]

Polo: everything is relative.

I can find nothing in my measurements of wear, indicating that I have significant change of camber - front nor rear.

[Lotus99]

Originally Posted by Tjalle

Presumably ?? new tires are 8.0 mm - anybody know? All in all 1200 km on tires.

Originally Posted by Lotus99

the manufacturers publish the new tread depth. I know Tire Rack shows it for each tire size

Originally Posted by Tjalle

Lotus: No INFO on Tire Rack - nor Pirelli - homepages.

It's right there on Tire Rack's specs page for the tire. It's the standard 10/32" tread depth:
.

[pokerface]

Originally Posted by Tjalle

pokerface, I saw no scary uneven wear on three tires - but on RR.

Thanks for tip, but I believe I have control of wear - will proceed as outlined above.
I can see no indication of "bad" camber. Uneven wear on RR I blame to too high tire pressure and Swedish secondary roads leaning to the right.

I would be very interested in your measurements of remaining thread after two seasons. Mileage?

Cost for 275/35-20" P Zero RFT is anything from SEK 3.000-4.000 (US$ 350-450).

Remaining tread depth wouldn't matter because it's relative to how much I've driven and how hard I drive it. Anyway, we only driven approx. 10,000 kms over two summers on these Pirellis... and as I've mentioned, the wear is very even all across and there's plenty left I think.

For what it's worth, I actually think decreasing tire pressures below recommended won't solve things but perhaps risk overheating the tire (leading to a blow out) and poorer handling. I actually bump my pressures up 2-3psi in the rear to get the rear to reduce understeer.

If you want to carry on the two year experiment of fiddling with tire pressures to balance out wear on that one tire, best of luck It looks like the consensus of the forum is that the best route is to pursue the alignment.

Anyway, to answer HighlandPete question, looking through Tirerack website, Pirelli P Zero RFT @ 275/35/20 have a stated load rating of 1874 lbs vs Pirelli P7 All Season RFT 245/50/18 @ 1764 lbs

[Tjalle]

Lotus: thanks for INFO - I did not find it - not used to visit Tire Rack.
10/32" is 7.94 mm - I take it Pirelli works in mm- should then be 8mm, which is what I assumed in my analysis.

Pokerface: thanks for your thoughts. I will test one year at time, and of course be very observant for any negative consequencies. I am very sensitive to steering precision and general handling - which to my mind is close to perfect after lowering and with 2.6 bars all around.

I will test the idea on my studded ContiIceContact 245/50-18 and have 2.8 front, 2.4 rear. Last winter I was running 2.6 all around. Thread is 11 mm - very little wear. Go to 2.8 rear when going for skiing in north of Sweden.