The subject has been covered in
Flight Testing. The thread provides links to references which associate SG with aquaplaning speed and also indicates that a simple formula might not apply to all aircraft.
In particular “
modern aircraft tires have lower hydroplaning speeds than those predicted by the well-known and commonly accepted equation … because of the differences in the footprint dimensions of the newer tires as compared to the older bias-ply tires.”
The diagram in the linked presentation indicates that the hydroplaning boundary ranges from 9*SQR x tire pressure to 6*SQR x tire pressure (psi).