Just wondering if anyone else has noticed their rear tyre pressure decreasing reasonably quickly? I set them up to the correct pressure when I bought the car (about 3 weeks ago) and I've done about 1,000 miles since then, but the light came on to tell me the pressure was low. I went to fill up and found they were down to 1.7 and 1.9. Fronts weren't too bad (both were on 2.00), so just wondered whether this was reasonably common or whether it'd be best to book my tyre guy to come and have a look at them?

Cheers

There's not an issue I'm aware of. Did you check with a proper gauge, or were you using a garage forecourt? If so, was it the same one that you originally checked them with? Just wondering if there's a discrepancy there...

I would also reset the TPM once all the tyres are upto correct pressure, just so the system knows where it's upto and what the correct pressures are. As it uses the ABS/ESP wheel sensor to work out when the rotation speed of the wheel changes. The reset procedure's in the handbook.

I was just using a garage forecourt tbf, but it was the same one as before. I've reset the TPM both times (when I first got the car and today) so I suppose I'll just have to see how long I go now before they need topping up again. I just thought it was strange that it dropped so much over such a short period of time, if you know what I mean.

Oky doke. As long as it was the same forecourt, then at least you know the readings are relative to one another

Could be a slow puncture of course. Just keep an eye on it I suppose...

A faulty valve could be another culprit, but again - that's rare and unlikely on more than one of your tyres.

Yeah, I personally think it's either a slow puncture or it's purely because of how many miles I've done in such a short amount of time. Won't be doing as many miles now though, so I suppose that'll give me an idea as to whether it's a puncture or not. It was only really the one that was particularly low (drivers side rear), so it is viable that it's a puncture/faulty valve. Just have to wait and see now!

I set all mine to 2.2 or in good old money 32 all round

I set all mine to 2.2 or in good old money 32 all round

Snap - or at least I think I do. The automatic inflator and hand-held pressure gauge do tend to disagree I stick with the hand-held to be consistent.

AshGSmith:

I've not had any front/rear discrepancies. Try checking them when cold rather than after driving to the garage. Being a FWD drive car it could be that the fronts build up heat (and thus pressure) faster than the rears and you see the difference after driving. You could also swap the fronts with the rears and see if the pressure difference follows them.

The TPM doesnt really tell you that the pressure is low it tells you that there is (a new) difference in tyre pressure. It is quite sensitive but if you inflate all tyres to the same pressure under the same conditions there is no reason why any one should lose that pressure relative to another within a reasonable time-frame of a few weeks which means that the TPM should not come on, at all. I would advise taking the wheel off and have a real good look at the tyre.

I have had mine come on once without apparent cause (but after several weeks without checking tyre pressures :-( ) and twice with dirt great screws in the tyres but that is in 30,000 miles.

Yeah I think if the TPM kicks up a fuss again in the next few weeks, I'll get the tyres checked over to see that there's no issues. It's a waiting game now!

Yeah I think if the TPM kicks up a fuss again in the next few weeks, I'll get the tyres checked over to see that there's no issues. It's a waiting game now!

I do recall when i first got mine I checked them and dealers didnt have them set right PDI my ring! But I checked again before a big journey must have been around a month later and the rears needed some air fronts not at all. Was surprised by this but didnt need any after my 3000 mile round trip or 2 months later as I kept a beady eye on them but my TPM didnt go off. Could it just be something to do with brand new tyres on brand new alloys its not like normal tyre change where it gets driven on straight away maybe this causes less of a good beaded seal until dome miles put on them

One oddball thing with tyre pressures, when checking from cold when car has been parked on driveway overnight for example, the side facing the sun can read higher than the shadowed side, obviously because the sunny side warms up the air. But it doesn't mean the tyres are losing air on the "low reading" side. I've noticed this a lot and checked by alternating which way round I park at night.

One oddball thing with tyre pressures, when checking from cold when car has been parked on driveway overnight for example, the side facing the sun can read higher than the shadowed side, obviously because the sunny side warms up the air. But it doesn't mean the tyres are losing air on the "low reading" side. I've noticed this a lot and checked by alternating which way round I park at night.

+1

Also, dont forget with the on set of Autumn and the cooler weather then the tyre pressures will drop as well. I think mine vary by up to 20 kpa from a hot day in summer to a freezing winter day.

The rear tyres on mine heat up more than the fronts even when on the max of 3bar. I check the temperatures using a calibrated hand ,especially when fully laden on holiday, and with push bikes on the tow hitch.

Pressure drop is dependent on time and not mileage IMHO. I'd suspect a poor bead seal or a slow puncture. I always use my own pencil type gauge.

Edited 31 August, 201114 yr by gregoir

Go with what has been said already - check in a morning when cold.

I have a had a very slow leak from the valve internals before - it just needed an 1/8th of a turn of the valve innards to tighten it up and stop the slow leak.

I would suspect the bead seal though on alloys as that is the normal culprit.

Try getting them filled with Nitrogen to see if that helps - it tends to stop the really slow leaks due to the larger molecule size or some such thing if you believe the marketing. Kwik fit will do this for about £1.50 a corner if you trust them anywhere near your alloys!

I think id getting them checked for leaks.

It will have nothing to do with the miles youve done 1000 in 3 weeks isnt that much.

I do 1000 a week and they dont lose any in that time.

In fact mine rarley need topping up between tyre changes to be fair.

I think I have only had to top them up half a dozen times in the last 11 months and thats 47,000 miles so far.

I have found the low profile VRS tires seem to be more effected by temperature changes then in my last car.

I had it the other way around. I set my tires when it was cool, and on a hot day the warning went off because pressure on the fronts was too high. Also not good as it causes the tires to wear out faster.

Try getting them filled with Nitrogen to see if that helps - it tends to stop the really slow leaks due to the larger molecule size or some such thing if you believe the marketing. Kwik fit will do this for about £1.50 a corner if you trust them anywhere near your alloys!

I prefer to fill mine with 79% Nitrogen and 18% Oxygen

I prefer to fill mine with 79% Nitrogen and 18% Oxygen

Fill 'em with a miture of hydrogen and butane - will make your car go with a bang!

Go with what has been said already - check in a morning when cold.

I have a had a very slow leak from the valve internals before - it just needed an 1/8th of a turn of the valve innards to tighten it up and stop the slow leak.

I would suspect the bead seal though on alloys as that is the normal culprit.

Try getting them filled with Nitrogen to see if that helps - it tends to stop the really slow leaks due to the larger molecule size or some such thing if you believe the marketing. Kwik fit will do this for about £1.50 a corner if you trust them anywhere near your alloys!

This will hardly put the cat amongst the pigeons but if wikianswers is to be believed any more than anything else on the web then nitrogen molecules are actually smaller than oxygen molecules:

For nitrogen, the covalent radius for a triple bond is 54 pm.

For oxygen, the covalent radius for a double bond is 57 pm.

Read more: http://wiki.answers.com/Q/How_does_the_size_of_a_nitrogen_molecule_compare_to_that_of_oxygen#ixzz1WiZiPynZ

This will hardly put the cat amongst the pigeons but if wikianswers is to be believed any more than anything else on the web then nitrogen molecules are actually smaller than oxygen molecules:

For nitrogen, the covalent radius for a triple bond is 54 pm.

For oxygen, the covalent radius for a double bond is 57 pm.

Read more: http://wiki.answers.com/Q/How_does_the_size_of_a_nitrogen_molecule_compare_to_that_of_oxygen#ixzz1WiZiPynZ

Ah, but it's a longer word so it takes up more space.

This will hardly put the cat amongst the pigeons but if wikianswers is to be believed any more than anything else on the web then nitrogen molecules are actually smaller than oxygen molecules:

For nitrogen, the covalent radius for a triple bond is 54 pm.

For oxygen, the covalent radius for a double bond is 57 pm.

Read more: http://wiki.answers....n#ixzz1WiZiPynZ

I did say if you believe the marketing

Quote from Kwik Fit website

Have your tyres filled with Nitrogen and increase tyre life by up to 25%, improve road holding and handling and increase fuel economy by up to 5%!

Filling your tyres with nitrogen may seem odd but that's exactly what motor sport and aviation professionals have been doing for years. Nitrogen is completely safe for use in tyres. By using it in a mixture with oxygen to inflate your tyres the theory is that it's possible to negate the issue of slow deflation, due to the larger nitrogen molecules taking longer to migrate from the tyre into the atmosphere through the tyre wall.

Having a tyre that does not deflate means you will improve fuel consumption and will probably improve safety standards too. It's not yet standard practice but Nitrogen could well be here to stay as a result.

Nitrogen inflation should only be carried out by professionals and should not be directly inhaled.

I did say if you believe the marketing

Quote from Kwik Fit website

Yes fair dos, I wouldn't believe wiki answers much more either . . .

Ours is set to 32 all round.

When filling/checking, as the tyres are usually warm from driving to the nearest garage, I always add 3 PSI. So on checking, they should all be 35, which when cold will be around 32.

Use the same method on my works car without issues.

I have mine at 40 now and prefer it - I have a garage down the road so the trick I have for warm tires is to over-inflate them when I return from a trip and then deflate them on my drive when cold to the pressure desired.

40 does seem excessive, unless you're running heavy boot loads all the time.