In a recent thread here, it came to my attention that many folks incorrectly believe that it is impossible to hydroplane a bicycle -- and, as a consequence, that bicycle tire tread is meaningless. Rather than bury this proof 3 pages deep in that thread, where it is arguably off charter, I am starting anew.

A 1963 NASA paper ( https://ntrs.nasa.gov/api/citations/...9640000612.pdf ) was offered in that thread as evidence that bicycles cannot hydroplane. Despite being 60 years old, it actually finds exactly the opposite to be true, as we will see.

That paper concludes that one can calculate the minimum possible speed for a vehicle to hydroplane with the following equation, Velocity = 10.35 * ( the square root of the tire pressure on the ground ) or V = (10.35 * sqrt(p) ). So let's apply that theory to the video evidence. The best example I have at hand is -- not even the most delusional posters here can deny that his motorcycle must be hydroplaning in that video.

So, in that video, Martin travels 63m, or 205 feet, across the lake surface. In the video, he estimates traveling at around 30 mph. We can confirm that, by observing that there are 5 seconds of footage of his bike on the water -- so his travel time is at least 5 seconds ( perhaps more, depending on how it was edited, but we don't really care as 30 mph is an easily-achievable speed on a bicycle ). So, his average speed on water was ~41 feet per second, or just under 28 miles per hour. Let's be generous to the disbelievers and call it 30 mph.

Now, we flip around NASA's equation, and after some arithmetic that's left as an exercise for the reader, we find that sqrt(p) = 2.89. Hopefully we all know that the pressure inside a pneumatic tire has to equal the pressure of that tire on the ground ( and the paper confirms as much, if you didn't know ). 2.89 squared equals 8.35, and 8.35 psi is an entirely reasonable tire pressure for a dirt bike motorcycle tire.

That means, per NASA in 1963, Martin's motorcycle in that video had to have tires inflated to ~8.4 psi or less, in order to hydroplane at 30mph.

So, contrary to the belief of many here, even in 1963, NASA was finding that hydroplaning cycles are entirely possible.


Furthermore, using NASA's vintage equation ( which is not perfectly accurate, and more modern research lowers the 10.35 constant, which lowers these speeds ), we find that a bicycle with 30 psi in its tires can achieve total hydroplane at 56.7 mph -- again, a completely achievable speed while descending. And a really strong cyclist could potentially hydroplane a fatbike with slick 4" tires inflated to only 8 psi by reaching 29.3 mph on level ground.

Also, as noted in that Purdue paper, "total hydroplane" is not really the important threshold. On a bicycle, your front tire is probably loaded lighter than your rear, especially if you are descending. That means your front tire may very well hydroplane at a speed much lower than your "total hydroplane" threshold, and once you lose your front end, you are typically in a bad way.

Hopefully now we all understand that continuing to believe that bicycles cannot hydroplane is akin to continuing to believe that the Sun orbits the Earth. There exists both video evidence countering that belief, and it is disproven by science -- many decades ago. It would be better for all concerned if the folks who do persist with that inaccurate belief at least choose to discontinue spreading that falsehood to new folks here.