[sylonien]

Hi,

been driving my BMW for almost 2 years and only just thought of this question.
How does the TPMS work? Does it need battery?

I recently had my two front tyres replaced, forgot to look for it to see what it looks like and would they have thrown it away? (I know might be bit of a stupid question). No idea on the subject.

It has warned me of low tyre pressure ages ago but since I've kept checking it and reset it so don't really have the warning anymore, which makes me worried whether its still working or the sensor still present?

Another thing, in the iDrive setting, under Units etc. There is a option for pressure Bar or PSI, which I never knew what it was for but I just watched a youtube video demo'ing the 6 series TPMS which displayed the pressure on each for corners on the display. How come mine doesn't do that, yet it has the option to set the units?

So confused!!!

[xenon]

On your car the TPS simply uses the ABS wheel sensors to measure rotational speed. If a tyre deflates the diameter decreases and it rotates faster than the other wheel on the same axle and TPS detects this. Hence there are no actual pressure transducers or batteries to be thrown away, and no units either as it's just relative. On the 5 and 6 series they use actual transducers in the wheel and therefore the actual pressure can be shown on the i-Drive.

[sylonien]

Aaaaaah! I seeee now. Thanks! Got worried about the whole thing.

Is it accurate that way or should I just check tyre pressure like every 2 weeks? I usually check whenever I hit 500miles or about 2-3weeks depending which one comes first.

Can the actual pressure monitoring systems be added to my iDrive?

And out of curiosity, do those units need battery etc?

[Springer]

I had the full system on my last Grand Cherokee. What a nightmare. Valves are ridiculously fragile. A tyre change could quite easily break them then it's another £80 on top for a new valve. I found then quite overrated and far prefer the BMW system!

I found it far more of a gimmick than a useful piece of kit.

Springer

[sylonien]

Come to think of it, I think I do prefer this system. Just in I'm stupid enough not to realise a puncture. But I will still stick to checking it manually frequently. Does seem to loose bit of air fairly, but not crazily quick over time. Normal I guess?

Like I said, 2.7bar rear, after 2 weeks around 500 miles it went down to 2.5~ ish, but that's just on one side. But surely that's not a slow puncture?

[AlwynMike]

Your tyre pressures should not change much at all - assuming that you have checked them at similar air temperatures and before you use the car.

0.2 bar in 500 miles I would say is a cause for further investigation.
It may be just a leaking valve (take the cap off and put a blob of spit over the valve - if it blows a bubble, that's the problem)
Worst case is a nail or similar still in the tyre, still mostly sealing, but waiting to come out at the most inconvenient time!!

The TPMS system won't alarm until the tyre pressure is significantly low - maybe around 60% of the pressure it was reset to. It's not accurate, as there are too many variables - temperature, reset, tyre size to name a few.

Mike

[sylonien]

Aha so by the time the warning comes, it means it's already seriously out? I will keep an eye out for it in the future.

Hm I can't remember whether it's the exactly same condition in terms of temperature. But I do always drive it off my drive and park it on the same spot, facing the same way each time to make sure its' similarly weighted. Not sure if parked on a slope would affect it so I try and do it when it's on level ground.

I might do that test tomorrow with the bubble.

Does seem to be the rear left that's loosing more or sooner. Just had MOT, surely they would of noticed if there's a nail or damaged?

And going down soooo slowly for 2 weeks?

[sylonien]

on the subject of tire pressure.
What should be the correct pressure?

I mainly drive with 2 people in the car including myself.
According to the sticker it's 2.5bar / 36.2PSI front and 2.7bar / 39PSI rear.
That is for RFT tires I assume 225/40/18 and 255/35/18 rear.

But I've got none RFT at the front now so I wonder if its' the same that applies?

I just downloaded a US copy of the manual and there's states lower pressure for the same condition? Saying it should be 33PSI front and 35PSI rear! Quite a bit lower?!?

[B33M3R]

Apparently, from Nov '12 all new EU supplied vehicles must have TPMS installed by law. I believe it also has to be the valve sensor based system, not just the ABS monitored rolling radius one. If so, expect lots more expense come new tyre time when the fitters snap them on removal 'accidentally' of course, then charge you about £60 for a new one plus re-coding to the car!

Still, a very good safety feature though....

[xenon]

I've seen some that are not connected to the valve in any way, they're just stuck on to the internal surface of the wheel, with a lithium battery that lasts about 5 years. There is no reason why a tyre-change monkey would need to go near it.

[doughboy]

Originally Posted by sylonien

Come to think of it, I think I do prefer this system. Just in I'm stupid enough not to realise a puncture. But I will still stick to checking it manually frequently. Does seem to loose bit of air fairly, but not crazily quick over time. Normal I guess?

Like I said, 2.7bar rear, after 2 weeks around 500 miles it went down to 2.5~ ish, but that's just on one side. But surely that's not a slow puncture?

Seems odd, could be a leaky valve. Make sure you always measure them cold in the morning. Often if you fill them at a garage your tyres, and thus the air inside, are warm so the pressure reading will be artificially high, then when you measure them cold the pressure seems to have dropped when its just cooled down.

0.2 bar would easily be the difference between hot and cold, maybe a lot more.

I only check mine every few months and they NEVER change TBH.

The last set of tyres, I never put any air in from the day they were fitted to the day I had them changed. Maybe dropped 0.1bar in 10 months, but I wouldn't bother getting the pump out for 0.1bar.

[sylonien]

What!?

Really? Well I use my own compressor to check so the condition should be the same except the temperature which I don't remember if they were the same but I didn't drive it before hand. Always check it before I drive, won't do it like after a drive.

Went out and checked and there doesn't seem to be any bubbles coming out from the valves when I checked using some water.

Anyone got any idea about the right tyre pressure?

[parapaul]

Pressures will be on the card in the drivers side door pillar.

[sylonien]

I know, just wondered if there is a difference depending on run flats or not? Since I've got RFT rear and standard fronts.