Craftsman 9.5 auger belt

My old auger belt was slipping so I purchased a new by taking the old in to the dealer . Installed new belt ,still slipping - I have maxed out the adjustment rods etc . There seems to be no adjustment available on the idler wheel of this unit
I have come to the conclusion , purchase a smaller belt . My dealer is not user friendly so . How do I measure the belt so I may source a smaller belt . Or is there a location for further adjustments on this unit
Any help would be appreciated
regards
Terry