Tyre Pressure Monitoring Systems

[Dave Liquorice]

Must be fun keeping that rotating joint pressure tight, I'm also having a trouble thinking out workable route... Sure you aren't mixing it up cooling water for the brakes, like some buses in China have?

Most "air brake" systems are vacuum operated, you need vacuum to pull the brakes off. Loss of vacuum is what causes those long skid marks you see from heavies on motorways. The vacuum from the tractor fails (interconnect hose disconnects or a joint develops a leak) and the trailer brakes come on, hard...

[Andy Burns]

I've seen 4 psi difference, doesn't need hours either ...

[ARWadsworth]

[Man at B&Q]

Can you give a link to more details of that?

MBQ

[dennis]

They have had systems like that on, some, military vehicles for decades. They are used to change the pressures to suit the terrain on the fly.

[McKevvy]

Why not use a normal tyre preure gauge instead of trusting technology?

McK.

[Roger Mills]

I do - but that only works when the stationary! I would like a warning if the tyre starts to deflate during a journey. Past experience shows that a tyre can be damaged beyond repair by running soft *before* it is detectable by my calibrated seat-of-the-pants!

[Steve Walker]

IIRC, you can just use (P1 x V1) / T1 = (P2 x V2) / T2

Assuming V1 = V2 (it'll be close enough)

And remembering to use absolute temperatures (Kelvin or Rankin)

You can work it out from there.

SteveW

[Steve Walker]

In my case, it wasn't a flat, but it *was* dark and absolutely pee-ing it down, plus we were on the A34 just South of Oxford, heading home to Manchester.

We were coming back from a holiday in France, along with our trailer (newly built, with brand new suspension/hub units, with pre-fitted, sealed bearings), when one of the bearings seized. The entire wheel, hub, bearings and stub axle disappeared into a farmers field and the trailer tilted over.

We managed to leave the trailer *just* off the carriageway, with a torch propped up illuminating a reflector. We made it to an all night garage and phoned for assistance. God were we lucky, our call was at 23:45 and our cover was due to expire at midnight!

SteveW

[Steve Walker]

I'm suprised that they use batteries. Modern sensors and transmitters should easily be able to do this while running off a capacitor and a charging circuit working off the vibrations of the wheel.

SteveW

[Steve Walker]

It's certainly do-able. Some heavy load transporters can adjust tyre pressures down to spread the load on softer ground and back up for tarmac.

Are you sure about that. I'm pretty sure that they are applied by the pressure of compressed air and that there is a backup system where loss of air from the system releases springs to apply to brakes automatically.

SteveW

[John Williamson]

Correct. *Some* artic trailers have an air tank which is charged from the system when the handbrake is released, and provides the application pressure instead of a spring, so that the brakes can be released for manoeuvring in the depot.

The only vehicle I've driven with vacuum brakes was a 1940 vintage breakdown truck.

Some very small artic units based on things like Transit vans have a vacuum brake on the trailer, but they are a maximum of 3.5 tonnnes gross weight.

[Huge]

Hummers (proper military ones) and some kinds of Unimog can do this.

[Man at B&Q]

It can take years and $M to get any new electronics qualified for automotive use.

MBQ

[Steve Walker]

Indeed and I should have put that.

SteveW

[Steve Walker]

Three times for me (excluding when I've been a passenger in someone elses car), in probably half a million miles.

SteveW

[Mike P]

I've had one when I hit a rock on the road in the dark, one on a motorbike

- rear blowout, a blowout in a Xantia 6 years ago, and one a couple of weeks ago where something slit the inner wall of a tyre. That's all, in

22 years on the road. I've had a couple of corroded alloys which the tyres have gone down on, but they weren't punctures.

[andrew]

All our trailers were like this, you had to pull a tit on the back of one of the 3 tanks to discharge it and release the parking brake if you needed to move the trailer without the tractor unit.

Stalwarts and DUKWs also could vary tyre pressure on the move, more recently some forestry lorries tried it too, to lessen damage to unsealed forestry roads.

AJH

[ARWadsworth]

Either you are very lucky or I am very unlucky then when it comes to punctures.

[andrew]

From my experience the number of punctures goes up in direct proportion to the number of builders' worksites you visit.

AJH