I left home in the car this evening, trundling at speeds up tp 20mph in traffic and wondering why the vehicle felt a bit sluggish and odd. Can't be a flat tyre, I thought - TPMS would have let me know. Anyhow, on to a faster bit of road - up to 30, then 40. Car definitely feeling very odd. Pulled over and found rear nearside nearly as flat as a pancake.

 

So why did the TPMS not let me know? Any thoughts gratefully received!

If the tire was already deflated so much before you have started your commuting, it can be sometimes very slow in detecting. Requires a visual inspection of the car before driving, but in general this good habit makes sense from many perspectives. 

The TPMS works by using the ABS sensors to measure changes in wheel rotations. This works well for tyres slowly deflating, but for quick deflation’s and flat tyres the driver should have notified it’s not so good. You can’t really blame the system for you diving off and driving some distance on a flat tyre.

Edited 3 October, 20196 yr by Kenny R

I take the point that I should habitually check all four corners before driving off.

 

However, I completely fail to understand why a system based on comparative numbers of revolutions failed to spot, and to spot quickly, the gross difference between a properly-inflated tyre (for which it was set) and a completely flat one.

 

This is the first car I've had with TPMS, and had it not been for the false reassurance from the TPMS that all was well with the tyres I'd have stopped to inspect them much sooner.

 

I still this this is really odd - particularly as it advised me this morning that the spare (215/60r16, cf. 225/50r17 standard wheels) was under-pressure - though it wasn't: presumably because of its very-marginally smaller diameter than the tyre it's temporarily replacing.

 

It seems to be straining out gnats and swallowing camels.

Edited 3 October, 20196 yr by Sangrail

@Sangrail

When did you last check the TPMS was working and reset to the tyres pressures, or change pressures or tyres and reset the TPMS?

 

EDIT, 

Sorry i see you had a warning with the spare on, so it was working.

so did you reset then so that it recognized that the spare wheel was on.

?

So how far had you trundled last night & when before that was the TPMS set?

Edited 3 October, 20196 yr by Roottootemoot

9 minutes ago, Roottootemoot said:

@Sangrail

When did you last check the TPMS was working and reset to the tyres pressures, or change pressures or tyres and reset the TPMS?

 

EDIT, 

Sorry i see you had a warning with the spare on, so it was working.

so did you reset then so that it recognized that the spare wheel was on.

?

So how far had you trundled last night & when before that was the TPMS set?

I'd gone about a mile last night before I realised something was wrong - though I still didn't think it was a flat tyre, as the wretched TPMS hadn't gone off.

 

I generally reset the TPMS when I check the type-pressures, every couple of weeks.

 

I can't remember whether I reset it after putting the spare on. Probably not, as I had other things on my mind (like being late....) - apart from which I didn't think it would mind the difference between the spare and the usual tyre, since it didn't notice the difference between the usual tyre completely flat and properly inflated.

I know that they can mind or recognize the difference with a spare on depending on the difference, and also can disable certain ACC type things with a Spare Wheel / Tyre fitted on some vehicles.

I have become very distrustful of the dumb TPMS on the Octy as it gives me lots of false warnings. Then again it did detect a puncture recently that was accurate but I didn’t take it seriously until the car felt different. I will be retrofitting the active TPMS in due course.