Sprocket gearing

[Val]

The less teeth, the less the sprockets (and the chain) last. I'd rather go + than -. Especially wouldn't reduce the, already small, number of front sprocket teeth.

It is more complicated than that. There is something called Same Tooth - Same Link. Means how many revolutions the chain makes before hitting the same tooth. For the standard front is 3. If you do -1 you actually have better Same Tooth - Same Link it will be 7. The biggest Same Tooth - Same Link number means less wear.

It is true that smaller front sprocket means more Tooth-Links contacts. Standard is 2628 per mile. With my -1 that gets worst 2816 Tooth-Links contacts.

In practice that means your front sprocket will worn a little faster. If you service your chain slack properly it will need several chains to run on the same sprocket in order this to have any effect.

If you do rear +3 you will have 2792 Tooth-Links contacts per mile. Means no difference than -1 front in wear terms.