Take 337 from Garner to Vanderpool/Utopia. It is one of the prettiest stretches of road in the area. Very curvy and lots of ups and downs. I would imagine a motorcycle ride there would be awesomely exciting. Just be careful! The Lost Maples Cafe in Utopia has some of the best food you'd ever want to eat! Ride on over to Lost Maple State Natural Area for a quick look see. Stretch your legs on the Maple Trail (very short but sweet "hike" along the beginnings of the Sabinal River). Also, there is a motorcycle museum of sorts not too far from LMSNA. I believe they have eats there, too, but have never stopped there.
To make it an all day thing, keep heading north, after stopping at LMSNA, on 187. Hit 39, head west to 83 then south through Leakey back to Garner.
editted because I didn't see your post about the Garner Loop! Oops...but maybe the stops I mentioned are a new idea.
