Extract from
PROCEEDINGS of the 2nd International Meeting on Aircraft Performance on Contaminated Runways. 1999
Caution large file – 11mb.
“Based on the results, Mr. van Es concluded that modern aircraft tires have lower hydroplaning speeds than those predicted by the well-known and commonly accepted equation developed by Mr. Horne of NASA. He stated that this was because of the differences in the footprint dimensions of the newer tires as compared to the older bias-ply tires.”
The diagram in the presentation indicates that the hydroplaning boundary ranges from 9*SQR tire pressure to 6*SQR tire pressure.