I usually get about 3 cassettes worth of mileage out of the middle ring on my triple. The other rings last much longer, being less used. And about 3 chains per cassette, so about 9 chains per ring. To reduce ring wear, ride more in your bigger ring. More teeth = less ring wear and less chain wear because of reduced chain tension. I wear the big ring more on our tandem because it has a bigger cassette and thus I tend to ride in the big ring and larger cogs which equals less front shifting. On my road single, the cassette is much smaller and I mostly ride in the middle ring, a 39T.