It looks like this is another important thing that I have been unaware of. Is the 5 year limit on tires a DOT thing or is it just what is recommended? I have always just used condition to determine if they needed changing.
There are many things that you will have to include when considering tire replacement based on age.
The 5 year rule is usually a conservative number. Most will last longer, but some don't make it that long. (A friend has 20+ year old tires on his bus & they still look & act OK, another friend (retired bus & truck mechanic) had a blow out on a 4 year old tire that was properly inflated & looked new.)
Aside from tread wear, there are many things that can influence actual usefull life of a tire:
- working environment
- storage environment
- abuse (over loaded, under inflated, curb damage, etc)
- length of non-use (rubber needs to be 'exercised' to keep the plasticisers where they are needed)
If not abused & used regularly, they can last much longer than 5 years.
How will an unexpected tire failure affect you?
Personally, I'll do all I can to have as fresh tires as I can.
I had 2 valve stems fail while camping & that was inconvenient to say the least, & yea I had a good spare . . . . but when 2 fail at the same time . . . .