TC1

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.

Chuck M 

Iride01 

Still you are disregarding in all your supposed video evidence, that the tires simply slipped due to other reasons instead of being lifted off of the pavement as is the requirement for hydroplaning even in the paper from NASA that you linked.

TC1

What "other reasons" enabled Martin's motorcycle to travel 63m across a lake surface?

If you want to pretend all those other videos do not show evidence of hydroplaning, you can bury your head in that sand, and I cannot stop you. So let's ignore them in this thread. I just provided with you mathematical proof that bicycles can hydroplane -- supported by NASA, and the NHTSA.

Argue with the proof -- if you can -- or admit that you are wrong.

Iride01 

Well first off, I don't see anything that doesn't look like fakery. To me it will seem that when the bike is going steadily across the water with a rooster tail, there is a solid surface just underneath the water.

As well his tires aren't bicycle tires. So why even try to bring this as evidence.

Unless the loss of friction is entirely due to the tires being lifted off the pavement by the water building up under them then it's not hydroplaning in my opinion. Or by any other definition I've read.

Even the scant sixty miles per hour he claimed in the video with his motorcycle tires, a person on a bicycle will have to be going way faster than that to ever hydroplane. And I don't think I can ride that fast even downhill. But I can ride fast enough for the lowered friction coefficient of a wet road to cause my rear or even front wheel, to slip out from under me.

Chill out dude! Is there a vein about to pop on your forehead?

Chuck M 

I'm not going to watch the video linked because I like riding bikes more than arguing about them on the internet. And because when riding on wet roads, tire spray is a bigger problem for me than hydroplaning.

Trakhak

From this page:

That is a very interesting question as I designed and developed bicycle tires for a couple decades. I will assume going full speed (60 mph +) in a straight line on a paved road, on 700 x 28c tires (which is today’s norm/average road bike size). I will say “no”, because the contact patch is just too small with all the weight of the bike and rider bearing down on the two tiny contact patches where water easily gets displaced.

I will add, that a complete slick tire actually works better, then a tire with any type of tread pattern, again assuming the bicycle is going in a straight line at full speed. Now once the rider starts to turn, that is a whole different story for the tire contact patches to maintain grip on a wet road. This is where tire compound, air pressure, and casing construction comes into play, and some combinations will grip better then others, but still hydroplaning is not a factor.

TC1

So the aforementioned mathematical proof from NASA and the NHTSA shows this bike-shop employee's guess to be incorrect ( check his c.v., 13 years in retail ).


I hope you have a better counter argument than that.

TC1

Guy Martin has a sufficient reputation that makes faking this video extremely unlikely. He holds or has-held many world records, certified by Guiness.

More to the point, his effort is confirmed by NASA investigations undertaken fifty years earlier.

Seriously? You can't understand the applicability?

Which is precisely what happens under Martin's bike... only the "road" is the ramp and the lake bed.

You clearly didn't watch the video, nor understand the proof. Please try to do both before commenting further.

Iride01 

Please try to understand that isn't a bicycle tire, at least not a human powered bicycle tire. So until you have some evidence that a bicycle can hydroplane at speeds bicycles normally travel, even in bicycle races, that I'll comment whenever I wish. This is after all a bicycle forum and it's public.

Any idiot can comment.

Perhaps you can try to ride out in a lake and show us some of your proof on video.

smd4

My 140 psi 23 mm tires cut through water like knife blades. Pretty sure I couldn’t hydroplane on a lake no matter how fast I was going.

Trakhak

You omitted to mention his having spent over two decades designing and developing bicycle tires. That's beneath you, I hope. Some of the NASA people might have worked after school as grocery store baggers, but that doesn't invalidate their data.

TC1

Again, try to understand the previously-posted proof. It is exactly what you just requested.

And there is no meaningful difference between the construction of bicycle and motorcycle tires, sufficient to render one immune to hydroplaning, and the other not.

Yes, you certainly can comment, if you like -- but doing so with your low level of understanding here is not doing you any credit.

Trakhak

No, you're wrong. After all, NASA says that ice skating is impossible because the blades would hydroplane.

GhostRider62

I've done well over 40mph in heavy rain on my bicycle.

I am not quite dead.

QED

TC1

Who the hell is still running 140psi in 23mm tires? If you are going to be that far behind the times, get yourself a Penny-farthing and be done with it.

Unsurprisingly, you are wrong. Your 140psi tires will achieve total hydroplane at 120.7 mph, per the NHTSA.

cyccommute 

Oh, I don’t…it could have something to do with the giant hydroplane under the motor case. It first appears around 2:00 minutes in the video. You can see it easily at around 2:30 as he does his run towards the water. At about 3:30 you can see the hydroplane skip off the water. The best view of it, however occurs at around 7:20 minutes where you can see it under the motor case from above…it’s about 2’ wide…and just a little further on there is a wide shot where you can see that the hydroplane from the side. It’s about 3’ long and extends to the rear axle. He’s got a great big ski attached to the bike and most definitely is not hydroplaning on the tires.

Here’s a quote from Solid solutions.

You can clearly see the hydroplane “hull” under the motor case. There are other videos and pictures around of a crossing of Lake Como where they put a ski on the front wheel to keep it from diving into the water. In essence, the motorcycle isn’t so much as hydroplaning across the water as boating across the water.

If you look at other videos of people crossing water on motorcycles, they are all using some kind of skid plate under the motor case to do it. Their tires are buried in the water up to the depth of the motor case.

The bicycles in your videos aren’t going anywhere close to the speed you, yourself, calculated. Your assumptions are also wrong. No one doing time trials is riding on 30 psi tires. Using the formula you put out there, at 60 psi, the speed increases to 80 mph. From this article, that is way too low. Time trials use 130 to 135 psi on dry conditions and drop 10 to 15 psi for wet days. Let’s assume, 125 psi. Hydroplaning doesn’t occur then until the speed is 115 mph. Odd how both of those values are just about what Sheldon Brown posted so very long ago.



You’ve provided no “proof”.

TC1

Ironically, you accidentally described how ice-skating works.

I'm sorry to say, but the level of technical knowledge on this forum is rather surprisingly low. Hopefully the knowledgeable people are just quiet.


edit: https://www.sciencedaily.com/release...1105104416.htm ( better article, same point )
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TC1

First off, it's nothing close to 2 feet wide, and second, you can see it flopping around like a soft fender, and third, the front tire is unaffected by it anyway, and fourth, and most importantly, the results achieved by Martin comport with the investigations by both NASA and the NHTSA.


Because, as I explained, the applicable constant has declined in the sixty years hence.

To be clear, are you admitting now that they are hydroplaning, or are you still delusional?


The question at hand, friend, was not "Is it possible to hydroplane during a time trial?" It is "Is it possible to hydroplane?" And people do ride with 30 psi in their tires.

Still an achievable speed when descending, or motor-pacing, or on an aero bike -- although very ballsy. Regardless, again, the question is not "Is it possible to hydroplane while riding the way I ride?" It is "Is it possible to hydroplane?"

Why is it odd? Brown used the same reference material, just older, less-accurate versions.

I have provided investigations by NASA and the NHTSA, both of which confirm that bicycles can achieve total hydroplane. I have provided video evidence of that phenomenon occurring.

If that isn't sufficient for you to understand, I daresay nothing ever could be.

shelbyfv

Maybe beng1 will step up for you.

GhostRider62

Realistically, how fast do cyclists travel? How many ride fast in rain? Or even ride in any rain?

I'm a stupid, lazy engineer. I don't need no stinkin NASA arithmetic to tell me hydroplaning on a bicycle is moot. Ain't happening.

But my top speed to date is only 67 mph but in rain I try to keep it to 40-45 mph.

GhostRider62

I don't think you have much experience on the bike. Lab wankers know squat.

TC1

Congrats -- I genuinely cannot decide if this comment is serious, or over-the-top parody. Either way, I'm ignoring it. If you honestly were attempting to participate in the conversation, turn down the "stupid" dial a few notches and re-try.

shelbyfv

We don't address folks this way on BF.

MaxKatt

same. Kennedy shot and some mad men pounding martinis and smoking a pack and a half a day do some “math” I’m supposed to have faith in now?