I've just bought a bike from my father in law, he hasn't had it long and the frame is a little too big for him so he sold it to me. not long ago he replaced the straight handlebars for a riser bar and he replaced the stem too. I think the handlebars are too thin for the stem because there is some movement when you lean on them, I took the Allen bolts out to check and there is a metal ring on the handlebars (I'm guessing to bulk them out so they will fit in the stem) but the bars wobble, mainly because the metal collar round the bars isn't the same length as the stem so the bars are only held in place round the small collar, not along the whole stem. I don't really want to replace the bars as they are just right for me, is there any way I can make them fit the stem (and if so, how?) or am I looking at buying a new stem?