timing belt--how bad is bad?

[LOACESQ@aol.com]

Hi List,

No, I'm not trying to take any insane gambles by pushing a t-belt to its
limits on an interference engine (MC).  I have t-belt, water pump, etc. on
order to do a change and won't drive the car till the job's done.

However, it seems that the t-belt must be of quite durable construction, and I
would imagine that it must show serious signs of deterioration before it is
ready to actually break.  Is this the case, or can it fail with little outward
signs?  What about small spiderweb cracks on the back of the belt that do not
go to the edges?

TIA!

Adam