OEM Metzlers Z08 long-term loss of tire pressure

I've noticed an extremely minor but still annoying loss of tire pressure on the M08's installed on the bike. At first I figured the TPMS is +/- 0.1 bar off but having double checked manually on separate gauges I confirmed the loss over time.

Recently I've done a test - prior to our summer tour 15th of July as we were going loaded and two up I've pumped the tires to 2.8 bar front and 3.2 rear that was a little over a month ago and some 2.5k kilometers or 1500 miles ago.

Today they've both come back down to 2.5 front and 2.9.-3.0 rear when cold.

The tires have 9.5k km or 6k miles total, no damages, punctures, or unusual wear and I estimate I've got another 1 to 1.5k miles in them (looking forward to going back to Mich Roads)

On my previous bikes (Dunlop, Conti, Michelin) I checked the tire pressures a few times a year and maybe in a year worth of time they would leak out 0.1-0.2 bar - so this is very new to me.
As far as can tell this was going on since new - is it a Metzler thing? Or could the tires have a insignificant seal imperfection from factory as more likely?

There is nothing wrong here . While your previous tires may of lost less there are still to many variables . Valve caps , valve core seal , corrosion on rim sealing surfaces , ambient air temps . You could also have ridden over a small thorn that may not appear to your eyes , but be causing a very slow leak .
As a former tire guy I've seen it all . Dyna beads caught in the rim lip will cause slow leaking tires .

Are you aware your TPMS also has temp sensor to accurately show the PSI ?

The bike is new (Dec 2022) and I checked the tires during washing several times now for any damages/punctures putting water or soap over any 'scars' or indents left by small glass or stone chips in the meat of the tire - since flung off. Numbers posted prior are when cold, when tires are up to temp the discrepancies remain i.e. 'loss' is still present when tires are warm and will warm up to 3.3 then 3.2 then 3.1. from 2.9, 3.0 as so on as the pressure is lost.

Rims and valves are immaculate in terms of any damage/corrosion/dirt and wheel weights are used for wheel balancing - no dyna beads, or any Slime-like repair substances used.

I guess it's possible some incredibly small and invisible one got trough somewhere and some minor pressure loss is expected over long time and miles but this is basically 0.1bar/month which seems to much.

copy and paste from United tire . FYI 0.1 bar is 1.45 psi , and is nothing to be concerned with over a month . In a day or week yes but not 30 days .

It exits the tire at the rate of 1-3 psi per month. The exact air loss is usually determined by the model and make of the tire. Different rubber blends provide different rates of permeation. About 1-3 psi per month is normal for air loss, but you still should check inflation rates often, and re-inflate your tires.

Do you check your pressures at exactly the same temperature each time? If not, use BMW's formula for adjusting pressure. If you want 42/36 and it's 68F temperature and your tires show 42/36, you're good. But what if the temperature is 78F? Then you should set your pressures at 43/37, and the TMPS will show 42/36.

Consistency is the key. Checking pressure "cold" means what...? First thing in the morning? Not all mornings are the same ambient temperature. Using the calculation eliminates uncertainty and gives you consistent pressures. Then, if your TMPS readings show a drop in pressure, you can surmise you're losing air.

Checking pressure once a month isn't sufficient, but that's just me. I check before each ride, but again...that's me.

It might be worth filling with nitrogen. Not that I’ve tried it myself in motorcycle tires, but the larger nitrogen molecules are less able to permeate rubber so I believe.

Tyres are porous. Some bead seals are better than others. Move on, nothing to see here

Zitat von Steady Eddie im Beitrag #6

---

It might be worth filling with nitrogen. Not that I’ve tried it myself in motorcycle tires, but the larger nitrogen molecules are less able to permeate rubber so I believe.

---