Checking Tyre Pressure

[Schwepps]

dear astroboy and schwepps....

Now I am really confused.....since I got my car, I have never checked my tyre pressure but I do sent it for alignment every 8-10k. I am using the idrive function and since it says the tyre is ok, i dont bother checking
If i do check it, and I have to pump some air, then do I need to reset anything in the idrive ?

Ebby, the first thing to understand is that we do not have a direct Tyre Pressure Monitoring System (TPMS) in our units. We only have a Run flat Indicator (RFI), which uses the data from the ABS to warn if one wheel is rotating at a different rate from the others. So it's an indirect measurement of tyre health. The RFI will alarm if you have a major air loss, but it will NOT alarm if you lose air gradually from all 4 tyres, or even from one slow loss puncture, as I have found in the past.

Astroboy's bravado is meant to be funny, but is confusing to the uninitiated. Frankly, I think humour is inappropriate on a subject as important to safety as tyre care.

It's best to check your air pressures regularly, and a BMW Advanced Driving Instructor was quoted in today's CBT supplement as saying one should check once a fortnight. After you pump your tyres, you have to reset the RFI in your OBC, or iDrive if you have one. This recalibrates the module that uses the ABS data. You don't need to be on level ground to do the reset, only about 10 meters of clear road to move the car forward smoothly. Hope this helps!

 

[astroboy]

Fact 1: Oxygen molecule is small, so it will seep through the tyre wall and gap. So tyre loss pressure over time and at the same rate for all 4 tyres which RFI will not pick up because the spin rate for all 4 tyres remain.

Fact 2: Run Flat tyre has thick side wall to retain its shape when pressure loss, so its impossible to detect visually for pressure loss, even the RFI can't tell if one tyre lost 5 psi. Only pressure gauge can tell.

So next question is what pressure is suggested for our rides?? I know there's a tyre pressure guide on the driver's side B-pillar but did u follow?

Okay, more confusing or "mafan" stuffs... not all petrol kiosk's tyre refill gauge are calibrated the same, always stick to the same pump for consistency or best use a personal air pressure gauge. (I don't have.. )

Want to know more? what is the ideal tyre temperature to preform a refill? When tyre is heated up after a drive, the pressure is inflated by a good few psi.. do y'all take this into consideration?

 

[Schwepps]

Agree with your fact 1 & 2, although it's not only oxygen that permeates, and it's mostly through the valves. Yes, I pump to the recommended pressures on the B-pillar sticker - 36/40 psi. Keeping them pumped hard ensures the lowest wear rate.

Your last para is wrong. Tyres should be pumped when as cool as possible, ie, straight out of the house. If you inflate tyres when they're warm, they'll cool to below recommended pressures. Warmed tyre temp varies a lot depending on ambient temp and the air pressure in the tyre. When I was driving my RFT on zero pressure after that last puncture, that tyre was not just hot, it was burning hot...untouchable.

 

[astroboy]

.. and when pump air, all loads like passengers and stuffs in your boot must be out of the car because these added weights will over rate the tyre air pressure... true? no?

Sometimes I wonder the B-pillar sticker guide was it meant for heated tyres because 36/40 psi seems to be on the high side and if I'm not wrong, there's a warning on the tyre wall that says MAX: 45psi. So when u pump to 40 psi when cool, once heated with load, you are near the max tolerable limit of the tyre.. isn't that dangerous?!

A more comfortable (as in peace of mind) tyre pressure range for me is 28psi to 35psi. Occasionally my MPV is running 39psi due to the load especially during holidays.

Unless RFT need to run harder in pressure.. but pump hard does not warrant slow wear, in fact it accelerate wear in the central tread. Better FC is confirm though. No wonder u can do low 11s in the per L/100km reading, which is pretty similar to my 4-potter.. or am I under pressure? as in under inflate?!

 

[Schwepps]

All no, especially your first para. Only your last sentence is a yes. 28/35 is the range for normal tyres, but not RFTs, which need to be at higher pressure. Your wear rate will be higher than mine for sure.

 

[astroboy]

All no, especially your first para. Only your last sentence is a yes. 28/35 is the range for normal tyres, but not RFTs, which need to be at higher pressure. Your wear rate will be higher than mine for sure.

Opsie.. time to visit the pump, regardless..

So do I go 36/40? Mine is 225/45R17 all round, unlike the staggered 325i :15:... and mostly single occupant.. Or better check my label again..

Actually another reason that turn me away from pump air at the kiosk is due to the high car jack rate in our neighbourhood... maybe its time to invest into a "personal pump".. :wink:

 

[Schwepps]

So do I go 36/40? Mine is 225/45R17 all round, unlike the staggered 325i :15:... and mostly single occupant.. Or better check my label again..

Your label will show that the heavier the load (5 adults + luggage), the higher the cool pressure should be. While you're there, check the sidewall markings of your tyres. If you're on real Bridgestones or Continentals, the max pressure should be 51psi. If yours are really only 45psi, it means you were fitted with ciplaks...or normal tyres.

 

[racheltoh]

I let the doctor fix my baby...He will be admitted to hospital *MPS AUTO* this Wed..etquah & ben...let me know if u r coming too this Wed..around noon. We eat lunch together..

Schwepps: basically what Manji told me is that i didnt check my tyre pressure regularly, thus cause the alignment to run. Then with my bad driving skill, ie: braking unnecessary ??made it worst. Anyway with this hot topic being discussed, i choose to let it fixed before changing the tyres 3 months later lo... And naively, Manji told me my front and back tyres are not of the same size boohoohoo.."i said, the bmw ppl (referring to forum) say ar...can rotate one wor" **so malu**

 

[bsoosay]

Hi there everybody,

Thank you all for the wealth of information provided. While its great to be reading all this information, yet a beginner like myself can easily get confused.

I pumped my tyres on Sunday. I'm using 225/45/R17 V91 (that's what is says on my tyres). The front tyre pressure is 230 kpa and the rear is 280kpa. After pumping my rear tyres, I used a tyre pressure gauge and checked one of my rear tyres and it showed me 260kpa. I doubled checked and saw that I was pumping 280kpa, but the tyre pressure gauge showed me 260kpa. What am I doing wrong here?

 

[Schwepps]

Rachel, I think you misunderstood him - having wrong tyre pressures won't make the alignment run. What he may have said is having low pressures will cause uneven wear, on the inner and outer edges of the tyres.

You're driving a 325i with staggered wheels, which means the front and back tyres are different sizes. What did you do? Move one or both fronts to the back and vice versa? If that's so, who's the nut who did that for you? You surely can't have done it yourself.

 

[Schwepps]

bsoosay, firstly make sure you're using a decent gauge such as a PCL, and not a cheap plasticky one. Secondly, petrol stations hardly or never calibrate their air pumps, so don't rely on the reading from the pump. The 280kpa showing on the pump will probably be less as wear and tear sets in.

 

[racheltoh]

My car is in MPS auto now. They took out the tyres ..

See..so rusty

Then the front tyres ...aged badly. See the wrinkles..

Luckily the rims still ok.

Decided to change new legs. So going for Non-RFT.
Climenta: that's the reason for the "burn"

 

[born crazee]

Hi all,

Suffered a similiar fate recently. A screw in the rear. You guys are right about checking the pressure periodically. Checked mine last weekend and found the screw. The idrive warning didn't show up at all.



See pics:http://shangsbmwe90.blogspot.com/

 

[astroboy]

Rachel, those wrinkles are normal if u drive her hard, all my tyres have those wrinkles even my 1.3L MPV.. Those are screech mark when you push her in the corner. Normal uncle auntie tyres no such mark. That means your tyres still soft and grippy.

I may have said many wrong things in the past but am pretty sure about this..

Damn! Must check my tyre pressure, butt dyno says my tyres runs a little soft now, no more jump jump over the yellow slow down marker on the road ever since I did my last BSRI service at IA...

 

[Schwepps]

Rachel, those wrinkles are normal if u drive her hard, all my tyres have those wrinkles even my 1.3L MPV.. Those are screech mark when you push her in the corner. Normal uncle auntie tyres no such mark. That means your tyres still soft and grippy.(

Got such thing meh? Then I'm a confirmed uncle lah.

 

[astroboy]

Got such thing meh? Then I'm a confirmed uncle lah.

Pheew.... thought u gonna say I wrong again..

Pass me your FOB and after a couple of U-turns, I can create the same wrinkles on your tyres.. :wink: ... and best do it with the DSC off.. I long time didn't off it lio, after that Pizza Hut incident...

 

[Schwepps]

Too many times say you're wrong no good mah. So I take one on the chin loh. What's a friend for, right?

 

[astroboy]

Darn... so I wrong again.. Maybe Rachel has been doing powerslides.. Those wrinkles normally appear at the tyre shoulder, due to cornering.. serious! No believe me?

Quoted from http://www.design911.co.uk/blog/index.php/2008/11/12/diagnosing-problems-from-tire-wear/

Diagnosing problems from tire wear.

Here’s a generic fault-finding table for most types of tire wear:

Shoulder Wear

Both Shoulders wearing faster than the centre of the tread

* Under-inflation
* Repeated high-speed cornering
* Improper matching of rims and tires
* Tires haven’t been rotated recently

Centre Wear

The centre of the tread is wearing faster than the shoulders

* Over-inflation
* Improper matching of rims and tires
* Tires haven’t been rotated recently

One-sided wear (Rachel's front right tyre suffer from this and it didn't mention air pressure.. )

One side of the tire wearing unusually fast

* Improper wheel alignment (especially camber)
* Tires haven’t been rotated recently (Forget about this because staggered setup with asymmetric tyre not posible )

Spot wear

A part (or a few parts) of the circumference of the tread are wearing faster than other parts.

* Faulty suspension, rotating parts or brake parts
* Dynamic imbalance of tire/rim assembly
* Excessive runout of tire and rim assembly
* Sudden braking and rapid starting
* Under inflation

Diagonal wear

A part (or a few parts) of the tread are wearing diagonally faster than other parts.

* Faulty suspension, rotating parts or brake parts
* Improper wheel alignment
* Dynamic imbalance of tire/rim assembly
* Tires haven’t been rotated recently
* Under inflation

Feather-edged wear

The blocks or ribs of the tread are wearing in a feather-edge pattern

* Improper wheel alignment (faulty toe-in)
* Bent axle beam


Meanwhile, found this alignment print out for an E39, before and after, notice the red means out and green means within... see how aggressive is the rear camber.. Mine is only -1.10

Before:

After:

... and these are E46Fanatic's reading he got from SC when he did the job there for RM360..

Rear Axle:
Camber -1:38
Toe + 0.09
Total Toe +0.18
Geometrical driving axis 0.00

Front Axle:
Castor 20deg: +7.13
Cross Castor: +0:01
Toe out on turns: -2:01
Cross Toe out on turns: +0.02
Camber: -0:54
Cross Camber + 0:10
Individual Toe : 0:05
Total Toe: +0.11

Tyre Pressures:
Rear 2.4
Front 2.2

Tyre Depth:
8mm (all 4)

These figures were taken back in March09, I wonder how's his tyre wear with those aggressive rear camber..

Again, as I mentioned earlier, these are only recommended settings but individual drive style may demand personalized settings to ensure equal tyre wear.

 

[racheltoh]

the wrinkles r inside...cant see it unless you remove the tyre.

 

[astroboy]

Hmnn... I still think u did powerslide.....

Old tyres will have many hair line cracks, I see yours very good.. :top:

Hair line cracks..

Aged tyres means old many year old tyre but yours I believe no earlier than 2006 la. Check the 4 digit manufacturing code and see the year, u'll know. 2006 tyres still safe to use la... but avoid them if u are buying them today.