Rear tyres deflating faster than front — but at the same rate

DocQuincy

I inflated my tyres in November, all fine. Didn't drive much over Christmas but went on a long drive about six weeks ago and the rear tyres were both down by about 12 PSI. Front ones only lost 2 or 3. Just inflated them again today and exactly the same: front ones lost 1 or 2 PSI, the rear both lost about 10. The front tyres are only about a year old but the rear ones, while older, are probably about 3 years old and haven't been used that much — so all tyres in good condition.

If it was one tyre deflating you'd think slow puncture but the fact they're both deflating at the same rate pretty much is odd.

It is due to be serviced next month. Should I have them looked at? Any ideas what could explain this?

I've looked at the tyres and can't see anything off.

On-the-coast

Alloy rims?
they often get leaky as they get older. 

Inflating tyres monthly would be a good plan - & checking weekly, or after periods of long non-use. 

Often tyres get changed as a pair - I wonder if the rims were greased adequately?

DocQuincy

Thanks.

It's a 13 Ford Focus with the alloys it came with. Other than once with my old car when I had a blow out I do change fronts and rears at the same time so you are correct that they are a pair.

Often tyres get changed as a pair - I wonder if the rims were greased adequately?

  Sorry, I don't know much about cars and didn't know alloys could do this. I'll flag it with the mechanic and also check levels more often. 

sheramber

leaking valves?

shiraz99

DocQuincy said:

I inflated my tyres in November, all fine. Didn't drive much over Christmas but went on a long drive about six weeks ago and the rear tyres were both down by about 12 PSI. Front ones only lost 2 or 3. Just inflated them again today and exactly the same: front ones lost 1 or 2 PSI, the rear both lost about 10. The front tyres are only about a year old but the rear ones, while older, are probably about 3 years old and haven't been used that much — so all tyres in good condition.

If it was one tyre deflating you'd think slow puncture but the fact they're both deflating at the same rate pretty much is odd.

It is due to be serviced next month. Should I have them looked at? Any ideas what could explain this?

I've looked at the tyres and can't see anything off.

If they're losing that much pressure in a relatively short period of time then yes, get them looked at.

On-the-coast

5 months is not a particularly short period of time.   Most Tyre use websites suggest 1-2psi loss per month is normal. 10psi in 5 months (approx) is close to that rough measure.

The Highway Code recommends weekly inspections. 

Nothing to be unduly concerned about - but do ask the question when you get it serviced - and check them again before then. 

On-the-coast

And… there’s a difference between checking then on a frosty morning before driving, and immediately after a 30 minute drive!

DocQuincy

Thanks @On-the-coast. I normally check before a long journey rather than every single month as we don't do much long distance driving but will try them again in a week's time and then book the service in and flag that.

If it was seasonal I would've expected loss in all four but the front two barely lost anything between Nov and March.

Boffinman

Rusty alloys will lose you air pressure. My old MGF was like that until I got the garage to take the tyres off and grind the rust off the alloys.

Ectophile

Sometimes tyres just aren't well fitted.  Some years ago, it bought a car with 2 new tyres on the back (to get it through the MOT) and two old ones on the front.

I went to a friendly local tyre place and got 2 matching ones put on the front.

Over the following months, I noticed that the back tyres kept going flat, but the front ones didn't.  Eventually, I went back to the tyre place and paid them a few pounds to take the back tyres off and re-fit them again.  They stopped going flat after that.

DocQuincy

Ectophile said:

Sometimes tyres just aren't well fitted.  Some years ago, it bought a car with 2 new tyres on the back (to get it through the MOT) and two old ones on the front.

I went to a friendly local tyre place and got 2 matching ones put on the front.

Over the following months, I noticed that the back tyres kept going flat, but the front ones didn't.  Eventually, I went back to the tyre place and paid them a few pounds to take the back tyres off and re-fit them again.  They stopped going flat after that.

Ah, thanks, that would make sense, as when I got the new ones a year or so ago, he put them on the front and moved the front ones to the rear. 
There everyone, I'll get it all checked at the service.