Tires: ST Tires, replacement wheels, rim width

Question
Your question was

Hi, I have a Terry 26b travel trailer that I purchased new replacement wheels
for and went from 15x6 wheels to 15x7. They have ST205/75r15 tires on them and I
didn't realize they were different in width before I gave my old wheels away.
The major tire chain that I bought the new wheels from said the existing tires
will fit the new wheels just fine and I will not have any problems becase of the
extra inch in width. Can you please tell me if they are correct or should I
replace the tires with wider ST225/75R15's that I don't know would even fit
without rubbing. I just purchased the existing tires very recently as well and
would hate to lose all the money on them (plus having to change the spare as
well!). I REALLY appreciate your help and time! Thanks!

Answer
Seth,

The allowable rim width range for an ST205/75R15 is 5" to 6 1/2".  So the rim is outside the range.  

Using a rim that is too wide will tend to de-arch the tread surface and cause the shoulders of the tires to make more contact.  This may lead to wear problems - although with ST tires, it is time rather than wear that is generally the deciding factor for removal - and tend to over heat the shoulders - and that is really bad because ST tires are kind of marginal structure-wise and increasing the heat being generated may lead to a tire failure.

So this comes down to how much risk you are willing to accept.  If you live in a hot climate - like Phoenix - I would advise you to fix this.  If you live in a cold climate - like Minneapolis - it's not so bad.