I’m hoping I can pick your brains to see if any of you have personal experience with drive belt failure.  I see in the Café that MMRanch had a belt failure on his Meteor.  I am very interested in any observations he made prior to his failure.  Any cracks or other defects noted?  The factory tech manual doesn’t provide much for inspection criteria.  Maybe some of you have a bit more to offer.

About 3 months ago, I inspected my belt during a routine service.  At that time, the belt had about 86000 miles on it.   I noted some unusual grey/white marks in 20 different locations on the belt.  Every place I saw a grey/white mark, closer inspection revealed a small crack.
This is a picture of a typical defect site.

This shows the depth of the worst crack.  It is the only crack that runs to the edge of the belt so it is the only crack that I can get a feel for the depth.

I haven't had a belt failure... yet. I can only give you my observations as to what might be happening.

Comparing the savage belt to others is going to be difficult. The savage belt is polyurethane/dacron vs. rubber/dacron that most bikes use. Our belt is basically a timing belt that depends on the lugs to transmit motion. Hence it does not rely on tension and excessive tension can damage it. Which is why most of us do not rely on the tension tool.

Because of the hard coating, don't bend or fold the belt tightly. This will stress the reinforcing fibers.

Over the years I've read several stories of belt failures and I don't think you'll be able to find a definite cause w/o looking several failures and knowing the history of each belt.

That crack could be an indication of localized failure that'll zip across the belt. Or it could last for many years. If the crack widens it certain cause for replacement.

I've been keeping an eye on it.  Doesn't seem to be getting worse.  I have a new belt in hand, but I want to see how far I can go with the original.  Just don't wanna end up stuck far from home.  I appreciate the comments.  Versy, interesting to learn about the polyurethane and Dacron, I would not have guessed that.  I thought the reinforcement was Kevlar.  Dave, good info regarding the grey/white marks.  That should make inspection for cracks a bit easier.

I can share that I do not run my belt tight.  I bought the bike in 2018 and it only had 1K on the ODO.  I don't recall if the belt was tight at that time, but it has been pretty darned loose for the last 87K.  When I first got the beast it had the classic belt squeak, but I got rid of that at around 3K by installing the double row ball bearing.  It's been trouble free ever since.  I never touch it except to change tires, remove the engine, etc.  It never needs adjustment.  I have been running the larger 27T front pulley for a very long time.

I've seen many V-belts fail due to external aging, to the point where the edges of the belt tear off and a belt can split completely across its length.

I've never seen a timing belt fail this way.
This is partly because they don't slip and therefore get hot.
With a timing belt, the teeth break, and this happens after cracks appear in the belt. If a torn tooth then comes into contact with another tooth, the belt suddenly becomes much tighter and breaks.

So, a good indication for replacement is cracks near the drive teeth, I think.