No stats to back this up but I've always believed that there a few good windows of opportunity for better deals on bikes.
September: riders returning to school decide they need the cash more than the bike; dealers are aware they're about to see the beginning of a long cold cash-less stretch.
October: previously hesitant riders who were holding onto their bike 'one more season' finally let go and put them up for sale, usually more determined to sell 'now' instead of letting the agony drag on to christmas.
November: the used-bike sellers now 'need' to be rid of their bikes; dealership sales are down and they're committing to holiday-season inventory... so offers are looked at more readily than mid-June.
December: Everyone with a bike for sale is gnawing at the possibility they could be stuck with their bike (or inventory til spring).
January: Motorcycle Show Season starts. Anyone overly anxious to take advantage of [non-existent, IMO] 'show specials' will need to dump their used bike quickly. Dealers of new bikes who take orders at the shows for new bikes experience 'pre-sales' fall-out where sales aren't actually closed. A few extra bikes are in the show-room with little hope of being sold til March-April.
February: your last window for the best deals because everyone in the bike-buying market is about to make a leap to their next bike (early, for better prices) or their first new bike (early, for dealers' early season incentives).
March 1st through to September 30th: occasionally good deals at either end of the riding season though generally the best deals will be on used bikes being sold for reasons other than a simple need for cash. Dealers will 'hold price' (ie: no screaming deals) knowing their inventory will eventually be sold through any one of the previously noted off-season gimmicks.
If there's a new bike in high demand that you MUST have, at least wait to buy it before or after [Nov or Jan] christmas. If you're just 'shopping', push your spending weight in the weeks following the (January) Motorcycle Show but not before. If it's a used bike you want, best selection & prices are NOW for the 'seller-motivated' factor. If you wait until late February or March, the same seller (if they're patient and not needing the cash) will wrongly believe they'll do okay if they just wait til the season starts again. Truth is: yes, they'll finally sell their bike but by then ...the same bike will now be up against 100+ other used bikes, depressing the price.
Again, not scientific... but I've been watching bike-buying/selling curves for about 30 years.
Good Luck!