Looking for suggestions on how to increase chain tension on my wife's Gazelle T9. There's no obvious adjustment I can find, and none mentioned in online or paper manuals. The bike is great and not at all old, and the chain has fewer than 500 miles on it. I had to run the B screw in full to bring a bit more tension to the chain but feel there must be a better way. She's losing the chain every other ride or so, and it spoils the outing. Any ideas? Thanks!