[chefwong]

BMW recommends 39/45psi for the M50
X5M it recommends 37/40psi


Just short of the X5M having 21" in the front, what's with the varying callout for the PSI with the 22"s.

Just dumped the summers and set it on 38/40 for now
Taking a bit of getting use to the tramlining coming back to these steamrollers from the super soft cushy winter shoes

No major potholeon the roads this season to be observed....I think last year, I ran 42 in the Rear. Trial and error on finding the sweet spot I suppose

[BlkGS]

Tires are a part of the effective spring rate of the system, higher pressure ein them, the spring rate goes up. They likely decided that the reduced air pressure combined with the smaller wheels and different shock tuning yielded some sort of advantage.

I've got mine set to what BMW recommended, no real complaints to make me want to change it.

[James_G0540i]

I run my 22"s on 34 front and 36 rear. We're in Summer atm, so I go a little lower as we get hot days, in Winter I might bump up the front to 35 and rear 37.

I also bump up the pressure by 3-4 PSI when I tow - which is closer to what the tyre wall label says.

I find the BMW recommendation too high, I've tried it and it gives a hard/harsh ride (too bouncy). I've spoken to a few mechanics and they tell me operating in the 35-38 range s fine and will also extend the life of the tyre a little. Running up in the 40s will shorten the tyre life.

[chefwong]

You must have roads of glass out there James. With fear of a sidewall bubbling, I can't see running the front at 34. Thx

[mushy_musashi]

Originally Posted by chefwong

You must have roads of glass out there James. With fear of a sidewall bubbling, I can't see running the front at 34. Thx

Im assuming his psi goes up to around 40/44 during driving simce he said he is on summer weather.

My door jamb says 41/45. When using the car in the morning, idrive recommends 40/44. I inflated my tire to 39/43 during a weekend morning. So far it goes up to 41/45 during normal driving when the tires heat up. This is still spring time weather. I might re-check it again and lower my starting psi when summer weather comes.

[Dandle]

I run mine at 2.6 bar front and 2.7 bar rear (both recommended at 2.4 bar in iDrive but I find that too soft).

[formerE36M3/4/5]

Isn't there a pretty big difference in recommended pressures on runflats vs non-runflats? I ordered mine with non-runflats.

[LDT]

I have 22" non runflat Pirelli P Zeros and inflate them to 38psi front, 40psi rear. Now at 8200 miles they are holding up well. The recommended pressures are too high IMO.

[James_G0540i]

Originally Posted by chefwong

You must have roads of glass out there James. With fear of a sidewall bubbling, I can't see running the front at 34. Thx

Our roads are OK but like most places there are some "3rd world" roads, but I tend to drive carefully and avoid large potholes.

As its Summer, I've seen my tyres at 34 go up to 37-38psi, its interesting how high temperature can make that sort of difference.

In Winter I do tend to go higher, but not much more, preferring to take the softer ride and more grip lower pressures offer.

I'd expect sidewall bubbling more with higher (over-inflated) pressures......

[poison]

The model of tire matters as well. My X6 has Conti Premium Contact 6's, and while they're 'good', and sufficient for normal driving, the sidewall is pretty soft. Coupled with the X6 mass, and I feel like turn in isn't as snappy as it could be. The app recommends 40 front and 44 rear. I recently boosted it to 46 all around, and it felt somewhat better.

When these wear out, I may try some more performance oriented tired. PS4's would probably transform the car.

[jad03060]

The higher the pressure, the higher the load rating…that load rating on the tire sidewall is at maximum pressure. Having less than at maximum pressure, the load rating is lower. Running them lower than recommended may allow excessive flex and heat buildup leading to increased wear, or failure.

You do not want to run them lower when at ambient (i.e., not after driving) than the label.

This may help with the explanation. Www.mr2-spyder.com

Now, most people do not run with the maximum load in their vehicle, so under those conditions, yes, you could have less than the label, but not if you then fill it up with stuff and people.

[Cityman]

Recommended pressures for my 22” Pirelli P Zero’s: 40 psi front, 47 rear.

[BruinMan]

I found this post and should help.

[jadatis]

On personscartyres only max allowed cold pressure is given of between 44 and 51 psi, and an ocacional XL 60 psi.
The reference-pressure, for wich the maxload is calculated for reference-speed of 160kmph/99mph, is 2.5 bar/ 36 psi Standard load, and 42 psi for XL/ reinforced /extraload.
US system 35 and 41 psi.

So you see a lot of those pressures recomended, not calculated anymore for GAWR's and max technical carspeed.
If it was calculated for max 99mph, outcome would then be much lower often, sometimes in the 26 psi/1.8 bar.

All to give less energy loss by tires. And if you use lower, you cant hold carmaker responcible.

So if you want to go lower, you have to determine pressure with acurate determined axleloads in your use.

I can make a cold pressure/axleloadcapacity list for your tire, with build in maximum reserve, at wich comfort and gripp is still acceptable.
For that I give 90% of calculated axleload-capacity for the pressure, for max 160kmph/99mph.
Calculated with my determined formula, that gives higher pressures then the official european for all kind of tires, I got hold of end 2007 and went running with.

Runflat or not is not important, I go from that information given on sidewal is right, responcibility of tire-maker.

Need maxload or loadindex, and XL// or SL.
The pressures I see you given and 21 inch makes me suspect you have XL.

[dnachmerp]

My dealer just replaced all 4 tires when i bought my cpo car and have 22 inch tires, and it's over inflated at 51 front and 58 rear with N2 air... WTH? you would think that they would get this right.... unbelievable...

[crabman]

Mine came with 55lbs all around. The max pressure for a PS4 is 50; on one of the tires that part of the label was right above the valve stem, but, who's looking I guess.

In any event mine is a 24 X5M, 22/21 PS4s, recommended on the door jamb is 35/39 cold for low speed driving. That jibes with the manual but the way I read it the door jamb is the one to pay attention to because it takes into account the installed tires.

[eelnoraa]

Originally Posted by crabman

Mine came with 55lbs all around. The max pressure for a PS4 is 50; on one of the tires that part of the label was right above the valve stem, but, who's looking I guess.

In any event mine is a 24 X5M, 22/21 PS4s, recommended on the door jamb is 35/39 cold for low speed driving. That jibes with the manual but the way I read it the door jamb is the one to pay attention to because it takes into account the installed tires.

I think 55psi is too high for tires with max pressure of 50. I would adjust so the max wont exceed 50, which is already very high

Typically, the lower the tire profile, the higher the pressure needs to be. And the higher the pressure, the less the tire deform under load, so more predictable handling. This maybe why X5m spec higher pressure. But then higher pressure also has less grip, more bumpy ride. So it is kind of a balance you have to find if you want to drift out side of factory spec

[crabman]

Your not wrong. I changed it at the lot to the recommended pressures. Under no circumstances should anyone be running their tires at a value above the tire manufacturers maximum inflation pressure.

Max tire pressure is the highest tire pressure to which a tire can be safely inflated, it is not a recommendation for operating pressures, by law it must be stamped or molded into the sidewall.

Recommended operating pressures in the US will always be on the tire information sticker which is usually located on the driver door jam. This number will never exceed the maximum tire pressure in any condition, high speed, loading, towing, etc

[jad03060]

As the seasons change and the average ambient temperature changes, keep in mind that the temperature does change your tire pressure (altitude does, too, but most people don’t change that enough to be a major issue). That’s one reason why they should be checked while cold…as you drive them, the temperature and pressure will rise at about 1#/10F. So, what might have been fine last winter, could be way too high in the middle of summer, thus the recommendation to check them at least once a month unless you live somewhere where the temperature is consistent all year long (not really that many places, plus, they do lose some over time, regardless).

Check and adjust them in your conditioned garage, then go outside and park, and the pressure could be way off from what it should be. The listed pressure is for the vehicle at ambient which could be quite different from where it was last parked and serviced, and, it could be different if parked in the sun on one side versus the other as the black tires will heat up just from that.

The TPMS display can be tweaked to show the internal tire temperature (at least in some MY with coding), and that can help get them where they should be.

[jadatis]

Once you determined the cold pressure for axleloadband max used speed, you can let it flow with ambiënt temperature.

There are 2 camps in this.
Camp 1: fill that cold pressure at any ambiënt temperature you drive in, be it 20 degr F or 110 degr F.
Only adyust for if you drive in other temperature then where you check it.
This is the largest camp.

Camp 2. Calculate back the cold measured pressure ( best definition is when temp of gascompound in tire is the same as outside the tire, so ambiënt, then compare it with determined needed cold pressure.

I am in camp 2 and not completely alone.
RIMEX and B-Allert write about the same.

Made a list to callculate by head acurate enaugh for the goal. In that search your determined pressure('s) and it gives howmany degr F it changes per 1 psi change. Then you only have to remember that.

I use 70 degr F as index temperature to calculate back to for easy calculating. But read 65, 68, 70 degr F.

Can also give list for Bar and degr C,

DegrC/psi/ cold 70-21/ degrF/1 psi
9 C/psi/ 18 psi/ 16 F/psi
8,5 C/psi/ 19 psi/ 15,5F/psi
8,5 C/psi/ 20 psi/ 15,5F/psi
8 C/psi/ 21 psi/ 15 F/psi
8 C/psi/ 22 psi/ 14,5F/psi
8 C/psi/ 23 psi/ 14 F/psi
7,5 C/psi/ 24 psi/ 13,5F/psi
7,5 C/psi/ 25 psi/ 13,5F/psi
7 C/psi/ 26 psi/ 13 F/psi
7 C/psi/ 27 psi/ 12,5F/psi
7 C/psi/ 28 psi/ 12,5F/psi
6,5 C/psi/ 29 psi/ 12 F/psi
6,5 C/psi/ 30 psi/ 12 F/psi
6,5 C/psi/ 31 psi/ 11,5F/psi
6,5 C/psi/ 32 psi/ 11,5F/psi
6 C/psi/ 33 psi/ 11 F/psi
6 C/psi/ 34 psi/ 11 F/psi
6 C/psi/ 35 psi/ 10,5F/psi
6 C/psi/ 36 psi/ 10,5F/psi
5,5 C/psi/ 37 psi/ 10 F/psi
5,5 C/psi/ 38 psi/ 10 F/psi
5,5 C/psi/ 39 psi/ 10 F/psi
5,5 C/psi/ 40 psi/ 9,5 F/psi
5,5 C/psi/ 41 psi/ 9,5 F/psi
5 C/psi/ 42 psi/ 9,5 F/psi
5 C/psi/ 43 psi/ 9 F/psi
5 C/psi/ 44 psi/ 9 F/psi
5 C/psi/ 45 psi/ 9 F/psi
5 C/psi/ 46 psi/ 8,5 F/psi
5 C/psi/ 47 psi/ 8,5 F/psi
4,5 C/psi/ 48 psi/ 8,5 F/psi
4,5 C/psi/ 49 psi/ 8,5 F/psi
⁸4,5 C/psi/ 50 psi/ 8 F/psi
4,5 C/psi/ 53 psi/ 8 F/psi
4,5 C/psi/ 54 psi/ 7,5 F/psi
4 C/psi/ 55 psi/ 7,5 F/psi
4 C/psi/ 58 psi/ 7,5 F/psi
4 C/psi/ 59 psi/ 7 F/psi
4 C/psi/ 63 psi/ 7 F/psi
3,5 C/psi/ 64 psi/ 6,5 F/psi
3,5 C/psi/ 70 psi/ 6,5 F/psi
3,5 C/psi/ 71 psi/ 6 F/psi
3,5 C/psi/ 75 psi/ 6 F/psi
3 C/psi/ 76 psi/ 6 F/psi
3 C/psi/ 77 psi/ 6 F/psi

[jad03060]

Bottom line, if you fill your tires when cold and the ambient is say near 0F, and you don’t check them again until the middle of summer when it’s 80F, they’ll be about 8# too high, and the opposite if you do it in the summer, baring any loss over time. IOW, you need to check and set your TP for the season. The recommendation is once per month, and if you do that, you should be close enough to the desired pressure unless the day you do that is way outside of the average days around it.

A very common issue is to set them in the summer, then come winter once it sits in the cold for the TP to show low, maybe enough to trigger the TPMS low tire warning, and for it to go out after you’ve driven some and the tires warm up, raising the pressure enough. The logic does not warn you if the TP is too high, but it triggers if it drops from the point where it was set enough. If you rely on tire rotation to announce TP problems, seasonal changes probably won’t tell you much, as all of the tires will rise or fall at the same rate, and that system is looking for differences BETWEEN tires versus looking at the actual pressure IN the tire. In that way, vehicles with TPMS are superior to those using tire rotation rates, but it costs more. Around the world, BMW seems to use both options. Note, the logic that shows a recommended TP is taking into account the actual tire’s temperature, which can indicate it is different from the label on the doorframe. IOW, if the TP is ‘correct’ at ambient, then you drive it raising the internal temperature by say 20F, the recommended pressure should be 2# higher than when they were at ambient. Once stopped, the tires will be cooling, so the ‘correct’ value will be changing, but that data may not be updated until you drive it again, so could put you in an incorrect situation…IOW, do it fast after a stop if you go this way so the tires haven’t had a chance to cool back down if you’re going to use the display’s pressure, versus the doorframe label.

For most people, just checking and adjusting them when cold monthly is more than enough unless you get into a special circumstance. It’s a good idea to check and adjust before a long trip.

[TXPearl]

I think we're overcomplicating this. The tire monitoring screen in idrive will tell you what the tire pressure should be based on the current temperature of the tires. It will adjust the recommended pressure as the tire changes temperature. Follow that and you should be OK (assuming you've got it properly spec'd with your tire/wheel combo and max speed parameters).