Tyre Pressure Warning

[Scapa]

Evening everyone

Just had another great long weekend away in the Cali, lots of sunshine and great countryside to walk and cycle. I noticed that for the second week after getting home (and tyres cold) one of my rear tyres was down at 39psi having set all tyres at 45psi before heading off. Even after a week the same tyre had only dropped to 38psi last week so either a slow leak due to not sitting on the alloy rim perfectly or a puncture which then seals (partially) either way need to get it checked.

The question I have is why hasn't my Tyre Pressure Warning indicator let me know I had lost pressure? I had reset it when all tyres set at 45psi as per instruction manual (pretty straightforward). Does anyone know if it only activates for sudden pressure drops or when a lower limit has to be reached before activating? Any advice appreciated.

David

 

[Martin]

As far as I know it only activates when there is a rapid loss of pressure.

 

[teeboy]

There are two types of pressure sensor - I think the ones you find on French cars are little pressure sensors on the wheels which transmit to the car if pressure goes down - this are the most accurate.

I think on German cars (at least on my BMW) they just work using the ABS sensors, but just detecting that the rolling circumference has changed, so it needs to be quite a big drop in pressure.

On the BMW it has to be well over 10PSI drop before it notices - I had a slow puncture for a while so I got into the swing of it

I assume the VW one is the same - I have it fitted on the Cali and never had a beep out of it.

The posh ones tend to show off, by actually telling you the pressure on the dash somewhere

 

[Scapa]

Thanks to both of you for input much appreciated. Will see about getting tyre checked anyway later in the week.

 

[Alan]

I have a slow air leak in my n/s rear tyre
I'm loosing approx 5 psi a week
The optional factory fitted tyre sensor seems to light up when when I'm about 7 or 8 psi down.
A few strokes on the styrup pump and all is ok for a couple of weeks
I really must get it sorted properly...

 

[shambly]

Yes, the Tyre pressure warning will trigger for a slow puncture, if the pressure has dropped sufficiently. At least, it has for me.

The system uses the ABS sensors to measure the speed of wheel rotation for each of the wheels. If one wheel is rotating at sufficiently different speed (due to smaller diameter because of the deflation) it will trigger the alarm.

(another example of paying VW £60 for something that is fitted to the van anyway...)

Simon

 

[Scapa]

Thanks folks for your input. Update is tyre had a small nail embedded causing slow puncture. As mentioned I was losing around 6psi over 4 days which hadn't activated the warning light. From your comments and experience looks like I may have got a warning after another couple of days say after 8 to 10psi loss or a more rapid loss if the puncture got worse.

Anyway puncture repaired and is now relegated to being the spare.