CREEP
Creep (tyre slowly increasing to a larger diameter over many hours after inflation) has only been noticed occasionally. I found it on some of my tyres including my new Continental Townride tyre as discussed above.
On page 7 of the article referenced above ( pdf file ) I analysed some data from Pete taken in September 1999 on his Kenda tyre. This clearly showed creep extending over two days after he pumped the tyre up. It was followed by steady deflation over the subsequent 5 days.
One would expect that small changes of tyre pressure would produce proportionally small amounts of creep.
The tyre is held together by nylon cords in the casing. These stretch as the tyre is pumped up. Most of the stretch is a normal reversible instantaneous elastic process. However unlike a springy metal, something else goes on in the nylon. The molecules can stretch a small amount extra slowly over a few days after the tyre is pumped, so we get what I have called "Creep". It does not seem to go on for more than a day or two. It is presumably caused by bonds between nylon polymers slowly being broken. Perhaps the period of creep completes more quickly at high temperatures than at low temperatures when one could imagine that bonds are harder to break.
By the way the principal reason why a tyre expands as the temperature increases is not due to the air pressure inside increasing, but the elasticity of nylon changes with temperature. It becomes "softer" as the temperature increases so it will expand more even if the air pressure inside is kept absolutely constant.
Our tyres are a miracle of engineering and have wonderful properties.