I used http://www.szynalski.com/tone-generator/ to quickly profile my hearing and found significant loss around 4.0kHz. I have ridden a motorcycle most of my life and it is much worse in the ear that is on the same side as the exhaust.
I am not sure what a spectrogram looks like for a motorcycle but I would have assumed that most of the energy is in the lower end of the spectrum, given the steady cruising RPS is around 40Hz-70Hz. But, your comment seems to suggest that there is not a direct correlation between the frequency of the noise exposure and the hearing loss frequencies.