To unlock bike #9 you need to unlock the 1st and 2nd Top Jams bonus tracks in Career mode. These are Gina's Hope and Camel's Hump. To unlock each bonus track you must beat the Ace time on the 3 tracks before it.
For example: you must beat the Ace time on Turndown 4 Watts, Nowheresville and Fumer to unlock Gina's Hope.
Basically you need to Ace tracks 1-3 and 5-7 in the Top Jams career back to be able to unlock bike #9.