Reading that some tyre manufacturers state tyres lose 1-3 psi every month because of osmosis, do other members find this true?

no, but then it does vary by 0.1bar per 10C or so... I'll be checking pressures when I wash both cars next week. Temp is scheduled to hit -20 so I'll set them to accurate at around 0C before it drops. If the pump says it's 2.4 across both front tyres I'm Ok with that if the flap says 2.3. 

 

Personally, across the A2, Fi and Octy, I don't see much air loss unless it's about seasonal storage. Generally the check is every couple of months and there's not much to do. I'll re-prove them when re-tightening bolts after swapping wheels. 

 

I think I'll start with a habit - every wash, check the wheel bolts, refill washer fluid, check oil, coolant, and tyre pressures. Will take about five minutes to do and ten to faff with the bolt covers on the Octy...

 

 - Bret

Edited 30 December, 20169 yr by brettikivi

Reading that some tyre manufacturers state tyres lose 1-3 psi every month because of osmosis, do other members find this true?

Possibly not as much as 3 PSI, but rubber is slightly porous - alloy wheels can also be porous and this along with the bead seal and valve stems can also cause losses. I believe reducing porosity losses was one of the benefits of using nitrogen - the other was for the lower and more controllable pressure rise as tyre temperature increases.  I have not seen a tyre yet that did not require reasonably regular checks. A good reliable dial-type pressure gauge can be had for the price of a few coffees.  In my experience modern radials tend to not visually show that they are down on pressure until they have lost quite a lot of air, to the point where it can seriously affect handling.     

Couple of points - check pressures when tyres are cold (in morning before car has been driven).

Many tyre pressure gauges are inaccurate, I invested in one that is certified to be accurate and the amount of times I have collected new cars or cars that have just been serviced and the pressure way out ( upto 30%) is frightening. I also ride bikes and a pressure variance of as little as 2psi can make a significant difference to handling. Also worth noting that pressure can vary by a few psi between winter and summer temperatures.

Edited 31 December, 20169 yr by Falconmick

Noted,once had a VW Caddy with steel wheels which started to leak air like a sieve.New tyres,valves.Made no difference.Finally had inner tubes fitted.Trouble was,inner tubes these days  are rubbish and were continually splitting.Put a ste of alloys on it and problem went away.

I believe reducing porosity losses was one of the benefits of using nitrogen - the other was for the lower and more controllable pressure rise as tyre temperature increases.    

Air is 78% Nitrogen so any change in porosity is small, and the more controllable pressure rise is because the production process removes water vapour - which is the main cause of pressure rise.

By volume, dry air contains 78.09% nitrogen, 20.95% oxygen, 0.93% argon, 0.04% carbon dioxide, and small amounts of other gases. Air also contains a variable amount of water vapor, on average around 1% at sea level, and 0.4% over the entire atmosphere.

 

the temperature vs pressure change is around 0.2bar per 10 C or 0.1F per 10 degrees F, apparently, and that chimes with my experience, which is why I tend to overinflate if checking and the weather's about to get cold. 

 

For you guys in the UK, this difference is essentially negligible. But if I go out and set them today at +6C, then next week at -25 things look a little different... I'm of the opinion that 0.1 bar here or there is not relevant. They need to be close to recommendations and the axle needs to be accurate. 

 

When I picked the octy up, it had summer tyres on. So far, so good. Then I dropped the winters on and the handling was awful. I drove it maybe 50kms on backroads and was extremely unimpressed. The cause was one rear tyre with significantly higher pressure than the other three....it was skittish, unsettled and gave absolutely no confidence. The Winter tyres came from the dealer, fresh on new OEM alloys....

 

 - Bret

Air is 78% Nitrogen so any change in porosity is small, and the more controllable pressure rise is because the production process removes water vapour - which is the main cause of pressure rise.

Thanks for that Dave - that does make sense, I hadn't considered the water vapour content. So a really efficient aftercooler / condenser on a air compressor could work almost as well?  

the temperature vs pressure change is around 0.2bar per 10 C or 0.1F per 10 degrees F, apparently, and that chimes with my experience, which is why I tend to overinflate if checking and the weather's about to get cold. 

 

For you guys in the UK, this difference is essentially negligible. But if I go out and set them today at +6C, then next week at -25 things look a little different... I'm of the opinion that 0.1 bar here or there is not relevant. They need to be close to recommendations and the axle needs to be accurate. 

 

When I picked the octy up, it had summer tyres on. So far, so good. Then I dropped the winters on and the handling was awful. I drove it maybe 50kms on backroads and was extremely unimpressed. The cause was one rear tyre with significantly higher pressure than the other three....it was skittish, unsettled and gave absolutely no confidence. The Winter tyres came from the dealer, fresh on new OEM alloys....

 

 - Bret

Hi Bret, so the dealers are on the naughty step. Again. Sad that we can not always trust the "professionals" in what they say or do. Another good reason to carry out your own checks when you can, but you really shouldn't have to. 

Changes in weather and atmospheric pressure can also affect tyre pressure.

Thanks for that Dave - that does make sense, I hadn't considered the water vapour content. So a really efficient aftercooler / condenser on a air compressor could work almost as well?  

Yep.

I inflated mine to eco pressures yesterday (36psi) there was 32psi from dealers, if nothing else the car seems to coast better in eco mode (dsg) and keep pace. Coasted nicely for over 1 mile into Welshpool at over 55mph at one point.

The big buts.

Unless you work on the tyre and the rim in a vacuum, you are always going to start with a tyre at one atmosphere, complete with oxygen and water vapour. Any amount of dry nitrogen then added is not going to make those unwanted components disappear. Dry air is of course better for preventing corrosion in the compressor system and any air tools used.