[Kerr]

Originally Posted by C.J

Well, I popped down to Tesco on the way home to top up the pressure on all 4.

To my horror, the fronts were now showing 14psi, and the rear 16psi. (After being sat for 9hrs at work).

Either the tyre place this morning misread my 60psi, and reduced it too low, or I have 4 tyres/alloys with a serious problem.

I've now topped them up to 37/40. I will keep an eye on them over the weekend.

Sound like you previously used a dodgy pressure gauge.

You've taken around 30psi out to find you are 30psi down on what you should be.

I doubt they all suddenly lost pressure if they held it before.

[Kerr]

Fronts should be 2.5 unloaded to 2.7bar with 2 passengers.

Rears should be 2.7 to 3.2 bar when loaded.

I run 2.7bar at the front and 3.1 at the rear.

Creepy coupe suggested running lower pressures to avoid inner wear? Surely that should be the opposite, more pressure to have the middle of the tyre protruding out from the inner edge?

The more pressure the more the swell in the middle surely?

[Dave_3]

Originally Posted by Kerr

The more pressure the more the swell in the middle surely?

Higher pressure, less easily deformed overall so will ride on its edge more.

D.

[HighlandPete]

Originally Posted by Dave_3

Higher pressure, less easily deformed overall so will ride on its edge more.

D.

Increasing pressure reduces shoulder wear on run-flats, as you run on the crown of the tyre, not so much on the stiff sidewalls.

One of the reasons run-flats wear so bad on the shoulders is the tyres take longer to warm up to full working pressure, so more time at lower than ideal pressure. Lots of short runs make the situation even worse, tyres hardly ever run at optimum working pressure. I personally run a couple psi higher winter time, just to compensate for this fact and reduce shoulder wear.

HighlandPete

[Dave_3]

Originally Posted by HighlandPete

Increasing pressure reduces shoulder wear on run-flats, as you run on the crown of the tyre, not so much on the stiff sidewalls.

One of the reasons run-flats wear so bad on the shoulders is the tyres take longer to warm up to full working pressure, so more time at lower than ideal pressure. Lots of short runs make the situation even worse, tyres hardly ever run at optimum working pressure. I personally run a couple psi higher winter time, just to compensate for this fact and reduce shoulder wear.

HighlandPete

I've always erred to the softer settings on my tyres and never experienced any edge wear. Most of my trips are very short. Mind you, I don't power launch off the line and increase my rear camber.


I had to juggle the pressures as I have Y rated 18" and they have a very different ride, load rating and suggested tyre pressures as on the door jam compared to the W rated 18" tyres. The Y spec tyres have much softer pressure settings.

I've found setting the pressure higher leads to a slightly more skittish and tiring ride. On my early E92 335D the dampers just don't seem able to cope with the increased, sharper jolts.

Either way, I hate RFTs.

D.

[C.J]

I've bought a 12v gauge/pump and just checked all pressures, and they are still correct (40/37 after 12+ hours).

I can only assume (and hope?) the garage yesterday morning misread the pressure, then dropped all four wheels to ~14psi. I can't imagine I was running 60psi.

That would make sense why my steering was incredibly heavy after I left the garage.

[HighlandPete]

Originally Posted by C.J

I've bought a 12v gauge/pump and just checked all pressures, and they are still correct (40/37 after 12+ hours).

I can only assume (and hope?) the garage yesterday morning misread the pressure, then dropped all four wheels to ~14psi. I can't imagine I was running 60psi.

That would make sense why my steering was incredibly heavy after I left the garage.

Unless they were mistakenly reading in bar and somehow converted to psi, rather than reading actual units, I reckon they had a really bad day.

41 psi if read as 4.1 bar = ~60 psi.

Only explanation I can think of, unless their gauge had blown, and everyone had 'wrong' pressures yesterday.

HighlandPete

[C.J]

Still no drop in pressure on all tyres.

Can only assume now the garage made a huge mistake.

[C.J]

Rear N/S is dropping around 6-7psi every 7 days. Other 3 tyres are holding pressure.

What are the possibilities? Cracked alloy/slow puncture/leaky valve?

[creepy coupe]

Get it submerged in a tub of water a look for bubbles.

[doughboy]

Brush a mixture of water and washing up liquid all round the tyre / rim joint and round the valve seat and valve top (cap off).

Bubbles will tell...

Do you have a Schrader valve removal tool? If so check the valve is screwed in properly.