How to keep tires from deteriorating

You could keep your model in case with a positive pressure nitrogen atmosphere (like the declaration of independence in the National Archive) but thats probably not very practical!

Otherwise the best best is to keep it out of the sun and in as low a temperature as possible. Alternatively, you can make a cast of the rubber tyre in resin and use that...but then again polyurethane has its degradation problems too.

Coat them periodically with WD-40 and they will last forever. The problem is that the rubber dries out and deteriorates. The WD-40 keeps it moist and it will not break down. It is the same problem with engine seals on a vehicle. If they are left sitting too long without being used, the seals dry up and deteriorate.

vespa boy, that is my problem: I live in Brasil, which is a hot country.

Gino, I will try that.

By the way, I was wondering if a spray of Testors Dullcote on the tires would to the job of sealing the rubber, keeping the rubber from contacting the air, and thus keeping its moisture inside, and so avoiding deterioration. What do you think?