Tyre pressure sensor.

[g6zru]

Come on jerbear, let us all in on it or is it a big secret?   

 

Fred

[g6zru]

Ooops double post.

[jerbear]

Sorry all, not sure what happened there.

I recently had a puncture on my 5 month old Yeti and the tyre pressure sensor failed to light up. Not sure how long I drove with it deflating but unfortunately the tyre is unrepairable.

I had a similar situation with a slow leak on my Octavia and the system worked fine, warning me before I did any damage.

Surely the warning light should have come on before?

As I ordered my vehicle with a spare I changed the wheel. When I pulled away the TPS light lit up until I reset it.

A little confused as well as a little poorer now.

[Yetiflute]

I have found that the detector is good with slow leaks - giving adequate warning that something is amiss well before complete deflation. Have had this useful and valid warning on about four occasions. However when I had a sudden deflation (which believe it or not I didn't notice), the system failed to warn me before I had driven some short distance home (about 1/2 mile) where I observed the expensive damage to tyre mysellf. So it obviously takes a short while for the system to decide you have a problem, however big or small it may be.

[g6zru]

I had TPM on my Roomster but it was more confusing than useful! I had a very slow deflation that it sensed and a fast deflation that it didn't!

I didn't spec on either of my Yetis...................

 

Fred

[jerbear]

It seems that as long as your tyre deflates slowly, your fine. Otherwise not too useful.

Really didn't notice the tyre had gone down which is a shame as it's just got me a new tyre.

[Paul52]

I switched my wheels at the weekend - front to back and vice versa - to even out the wear as I want to fit all-season tyres when these need replacing. After about 2 miles the TPM light came on, I reset it and have had nothing since. This would be consistent with the previous posts that there is some of delay built in before it triggers so it will detect a slow puncture but not a rapid deflation.

[ddyer79]

It seems that as long as your tyre deflates slowly, your fine. Otherwise not too useful.

Really didn't notice the tyre had gone down which is a shame as it's just got me a new tyre.

 

Do not underestimate the value of knowing you have a slow puncture.  Putting load onto  tyre that is deflating could result in rapid deflation and loss of control.

 

I, personally would not be without TPM, but then it all depends on the journeys you do and the distance you travel.

 

Travelling a lot on motorways as I do I'd like to know of a 5% differnetial in tyre pressure even though I check pressure regularly.

[Yetiflute]

I totally agree with the above. Despite my incident we really ought to be able to detect a sudden blowout without the need for a TPM. It is the slow puncture that it is very useful for and for which I admit I do not check my tyres often enough. I would order a TPM again for that reason. Now that I am aware it does not react instantly to a blowout I am more aware of the need to be alert for such incident.

[Brijo]

I switched my wheels at the weekend - front to back and vice versa - to even out the wear as I want to fit all-season tyres when these need replacing. .....

16"SpecialBuildClub question, if I may go OT for a moment, please?  What tyres did it come on, and how's your mileage going?  I'm just coming up to the second annual service, at 13K miles on Conti's.  I've asked for front-to-back wheel change (no, I can't do it myself) to even out the wear ready for a switch to all-seasons but it looks likely that the FNS won't last much longer.  The blame lies with the state of our local lanes - lots of broken shoulders and pot-holes.  So, at least two new tyres this autumn, it seems, at around 15K - not a very happy bunny  :S  . 

[muddyboots]

If you think about it, the way the TPM must work is by comparing rotation speeds of each wheel.

A tyre that is of lower pressure will rotate faster than the others, as on the affected wheel, the radius between the centre of the wheel and the road decreases (but the vehicle speed remains the same).

 

The only time your wheels should be turning at the same speed, is when travelling straight ahead.

When you steer, all wheels will follow a different radius curve, and all be at diferrent speeds.

 

So I expect the TPM only looks at wheel speeds when the car is travelling straight ahead, and then averages over a decent length of time, to ensure it doesn't give false warnings.

That would explain why it catches slow deflations, but sudden deflations could catch it out.

 

That's my theory anyway

[DonjSZ5]

see Indirect TPMS here

 

http://en.wikipedia.org/wiki/Tire-pressure_monitoring_system

[Paul52]

16"SpecialBuildClub question, if I may go OT for a moment, please?  What tyres did it come on, and how's your mileage going?  I'm just coming up to the second annual service, at 13K miles on Conti's.  I've asked for front-to-back wheel change (no, I can't do it myself) to even out the wear ready for a switch to all-seasons but it looks likely that the FNS won't last much longer.  The blame lies with the state of our local lanes - lots of broken shoulders and pot-holes.  So, at least two new tyres this autumn, it seems, at around 15K - not a very happy bunny  :S  . 

 

The tyres are Continental ContiPremiumContact2. I've done just over 10,000 miles and have around 2mm left on what were the fronts (before I wear down to the indicator marks) and 4mm on what were the rears so I would guess my wear rate is petty much the same as yours despite the very different specifications of our two cars. I can't see them making 15,000 miles. My driving is mainly around Hampshire and West Sussex where the road surfaces are generally pretty good. I'm getting a regular 40mpg from the 1.2 petrol engine with a high proportion of short trips, so it's not excessive wear through an aggressive driving style. As it looks like my tyres are going to need replacing soon after your own I would be very interested to hear how you get on with an all-season tyre when you change.

[muddyboots]

Well, I post in a thread about the TPM and guess what happened today - got a tyre pressure warning.

 

I bought a new set of tyres a couple of weeks ago, and got them swapped on yesterday. A few miles after leaving the tyre place, the TPM warning pops up. 

I stopped to check, and they all looked fine, so continued my journey home, but a little more sedately than usual.

 

Checked them all today, and all the pressures are equal.

 

The pressures on the previous set were all equal too.

 

Guess I'll have to reset the TPM on the next journey, but it does seem odd. It's perhaps more clever than I thought. Perhaps the rolling radius of worn-out tyres compared to new tyres is enough to make it think something is up.

[KBPhoto]

Perhaps the pressures of the new tyres are different to the old ones. Quite common for tyre places to get pressures wrong in my experience.

I suggest trying to remember resetting the TPMS after tyre / wheel changes and after changing tyre pressures.

That reminds me! I've just let mine down after a fully loaded trip where I pumped tyres up.

But the TPMS never went off when I pumped them up / let them down at the start of the week despite pressures going from 2.2 bar to 3.2 bar (rears)...

[Huskoda]

Due to the way it works it will only pick up slow punctures, which are also the harder ones to discover. From personal experience you don't need a computer to tell you one of your tyres has suddenly gone flat.

 

Its because it measures the revolutions of each wheel compared to the gearbox output and alerts as one starts to drift from what it recognises as normal. But because the car goes around corners or over uneven/slippy ground, it can only alert you after it has been measuring for some time, or you would be bombarded by constant false alerts.

[dutyhog]

My TPS went off again today at the same spot on the road as the only previous time, a week ago (the car has only done 450 miles so far). Each time I couldn't detect any pressure loss. I just assume that the very uneven and wet road made one side slip a bit, and fooled the sensor.

[john999boy]

I've got this sort of system on my Tiguan.

Over the past few months I kept noticing one tyre that always sometimes had slightly lower pressure but I couldn't seem to see anything lodged in the tyre so just presumed it either wanted re-seating or the sensor was maybe on it's way out. Anyway, after getting tired of regular topping up, I went to the local tyre depot and sure enough, after doing a bath test with no leaks detected and then a loooong search in the tread for foreign objects, we found the thinnest of nails.

Obviously the tyre flexing wasn't that much to cause big problems and the recent heatwave meant the tyre pressures kept increasing/decreasing on a daily basis. However over a period of maybe two weeks, I could guarantee that it needed pumping up as it would by then be consistently 0.1 bar lower.

The added advantage of this system over the 'normal' system is that it doesn't need resetting to ensure correct functionality.

[Devil's Chariot]

TPS has saved me twice with slow leaks now in 21 months; wouldn't be without it

[gadgetman]

The usual cause of failing to detect deflation is not regularly checking and resetting the system.

When you reset you're not setting a pressure. What you're doing is setting a reference for all 4 wheels.

What the system is looking at is one tyre deviating from the others. As tyres naturally lose pressure, if all tyres drop equally the system won't tell you.

If however you inflate/change tyres and don't reset, each tyre revolution will increase since the last measure taken by the abs sensor and the system will trigger.