Wireless tyre pressure monitoring?

[Tim S]

John coughed up some electrons that declared:

MINIs do that, or at least the latest revision.

Cheers

Tim

[Roger Mills]

Dunno. Mine doesn't. Besides which, I don't know whether that would work. There is a school of thought which says that the distance covered per wheel rev is determined by the amount of tread laid on the road - rather than 2 x Pi x standing height. If that is that case, a soft tyre would not rotate at a higher speed than an inflated one.

[Bob Mannix]

No, that's why he said "over a significant distance" and "consistently". The clue is in the words :o)

[The Natural Philosopher]

So no use for rallying then ;-)

IIRC F1 cars use some kind of ride height sensing..any assymmetry in the hat when going straight, is a puncture..

[John]

[John]

A lengthy article here:

[Roger Mills]

Using the existing ABS speed sensors is clearly cheaper than having pressure/temperature sensors in the wheels - but has to be designed into the car rather than being suitable for after-market use.

I'd still like to find someone who is using an after-market pressure monitoring system in the UK - in order to find out what is available, and whether it works ok. Surely there must be *somebody*?!

[Tony Bryer]

The article referenced in another post says "The rolling radius of the tire becomes smaller in proportion to the rate of deflation and therefore the wheel speed of the deflated tire increases."

Surely if the length of the tread is 1.5m (and if it's a steel belt radial or similar so won't change with inflation/deflation), travelling this distance causes the wheel to rotate once whether fully inflated or running on the rim?

[Roger Mills]

That's my feeling too! But them what make pressure monitors based on change in radius seem to be claiming otherwise.

[Nick Finnigan]

With lower pressure, the tread gaps will be able to close up a little, which will change the 'tread length' more obviously than it will change the 'rolling radius'. The article is claiming a 3mm /1% difference, which seems plausible, but you would want to cover a long distance before deciding the difference in rotation wasn't due to roundabouts.

[The Natural Philosopher]

Not quite.

The outer layer of tread can be fairly expanded on a fully inflated tyre, or rather compressed on a rather deflated one.

Also you can get slip under traction..

[Mike Barnes]

Rather than guessing whether you've been driving in a straight line or not, surely it makes sense to monitor the steering.

[Nick Finnigan]

Yes, or the lateral acceleration, if there was already a sensor monitoring either of them. Otherwise use the existing ABS sensors and some less-stupid software in the controller.

[Dave Liquorice]

Agreed no tyre will survive long if internal surafces are being forced into contact even just briefly on bumps. That I would call "flat". Soft is when there is still pressure in the tyre but it's not enough and the shape is visibly different and the handling noticeably altered. This is with normal tyres mind not a thick rubber band...

If a tyre picks up a puncture and goes flat when running the chances are it will be killed but a slow leak where you loose just a couple of psi/week should be picked up by visual observation/change in handling(*) or if those don't occur 'cause rubber bands are fitted rather than proper tyres you'll have to resort to actual pressure checks.

(*) Trouble is modern cars are very reliable, just feed them fuel and drive. Take them to the garage to be serviced occasionally and get the MOT if it's old enough to require one. Many drivers simply don't notice via the handling or bother to look for a soft tyre. To me a normal profile tyre that is 5 to 10psi down is very obvious.

[DervMan]

Yeah I do. Old military habit. Pressures and tread depth is checked around every 2,500 miles, more frequently for new tyres.

It is. Fortunately, this car has the lowest profile tyre I've yet owned, which is only a 215/55/16, so it still looks like a tyre.

...and are of course unproven in any application until you've had them for a while, too.

[Ret.]

I fitted a set of those valve caps that show a red strip when the pressure drops. They were just under £10 for the set and work a treat. When I first got them I kept a check on them with a digital pressure guage - but I'm now happy that they work accurately and a quick visual check when washing the car is all that's needed. I've had them on for over a year now and they haven't been nicked yet.

Ret.

[Peter Hucker]

Wouldn't work here - I have never washed a car. Why wash something which will get dirty next time you use it?