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Everybody knows about hydroplaning----Right? Wrong!
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l8sho
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PostPosted: Thu Sep 05, 2013 11:29 pm    Post subject: Everybody knows about hydroplaning----Right? Wrong! Reply with quote

I hesitate to tell this story because in the past when I've told it, some have stopped just short of calling me a liar. If I'm lyin', I'm dyin'.

Everyone who has driven in a spring shower, or sat through a few hours of driver training think they know all there is to know about hydroplaning. Most of them are wrong.

Many years ago when I was living in Germany, I had the prettiest little US spec red '70 Type 1. Took good care of it as I do with all my vehicles, including good tires.

I was going home late one night after my second job. It was about 10 miles of very good two lane blacktop. About half of it was nearly as straight as a string with just a few gentle curves. That stretch had been recently repaved and was as smooth and flat as a billiard table.

It had been raining steadily since early evening but that didn't really concern me. There was never anyone else on the road at that time of night and I could drive it in my sleep. Actually, I probably did just that more than a few times.

It wasn't raining all that hard and the wipers were easily keeping up with it. I was running about 55 when I noticed the speedometer had stopped working. It was kind of annoying because speedometer cables usually give some warning before they break, and this one hadn't. While I was thinking about when I'd get a chance to replace it, the speedometer suddenly read 50. I remember thinking, "that's strange", but started picking up speed again. The speedometer went to 0. I slowed a bit and it went from 0 to 50 in about the time it takes to snap your fingers. I gave it just a little gas and watched the needle creep towards 55. Just as it got to 55.....snap....0.
I did that half a dozen times. Every time it was exactly the same story ...55....snap...0 ---- slow slightly .... snap...50. Obviously the left front wheel was climbing on top of the water and stopping as if the brakes were applied. If it wasn't turning, then it seemed likely the right front wheel wasn't turning either. Yet I was running at least 55 mph. This couldn't be good! Just a puff of a crosswind and I would be in the ditch. Needless to say, I slowed down, and watched the speedometer the rest of the way home.

Before the Samba know-it-alls say, "Well of course -- its VW -- no weight on the front end", let me tell you about a film I saw a few years ago. Goodyear tire engineers experienced exactly the same phenomenon with a full sized car on their test track in about 1/2" of water. At about 60 mph, the front wheels simply stopped turning and didn't start turning again until they slowed the vehicle. The rear wheels continued to turn presumably because they were driven.

I understand that a tire can push water until it climbs on top and loses traction. I DO NOT understand why it instantly stops turning altogether. But I know for a fact that it can happen. Does it happen all the time? I don't know.

So the next time you're blasting down the freeway in a rainstorm....think about it! (Especially if you're on marginal tires, or those wide low-profile donuts.)
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theastronaut
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PostPosted: Sat Sep 07, 2013 9:58 am    Post subject: Reply with quote

I drove my mom's new beetle in the rain once. Hit a small stream of runoff while climbing a hill with the right side wheel... the wheel pulled to one side and the speedo went to 90. I let off the gas and the speedo would fall, or I could hit the gas and it would keep climbing until I let off. The other three wheels were still fully touching the ground (right front was pushing water out of the way for the right rear) so it was still very stable. I thought it was pretty interesting. My buddy has a Geo Prism that does the same thing.
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l8sho
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PostPosted: Sat Sep 07, 2013 10:26 am    Post subject: Reply with quote

Interesting indeed. But of course, easily explained. I wish someone would explain to me why an undriven wheel suddenly stops under similar conditions.
cd
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bubblehead
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PostPosted: Sun Sep 15, 2013 3:38 pm    Post subject: Reply with quote

Im hardly a physicist but think about it like this. If you do a wheelie on a bike the front wheel stops turning. Once the little bit of rotational momentum wears off there is nothing to make the wheel rotate even though the bike is still moving. When it comes back down to the pavement it encounters resistance which causes it to spin again. The resistance of the tire on the road is trying to stop the wheel, but the forward momentum of the bike forces the wheel to turn. Now when you hydroplane, the water separating the tire from the pavement eliminates the resistance that the wheel is trying to overcome and it stops spinning. The weight of the wheel and any wheel bearing drag will also contribute to this. Make sense? Wink
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l8sho
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PostPosted: Sun Sep 15, 2013 4:33 pm    Post subject: Reply with quote

bubblehead; I'm glad that someone has finally attempted explanation. Does it make sense? I don't think so. Yes, of course, an undriven wheel will eventually stop turning when it loses frictional contact with the surface that is contributing to its momentum. Bike wheels, aircraft wheels, VW wheels, all the same. But the problem with your theory is that momentum. None of those wheels, spinning at better than 50 mph, will lose its momentum instantly. Take that bike, put it on a stand, spin the front wheel as hard as you can by hand, and see how long it will take before it stops due to friction in the bearings, air resistance, etc. If it is in good shape, it will take several seconds at least..........and that's going to be at maybe a couple of mph ....nothing like 50+mph.

You mention the weight of the wheel. Actually the weight of the wheel will be the primary factor in keeping it turning (the flywheel effect). The heavier the wheel, the more kinetic energy it stores, and the more it resists stopping. It most definitely does not want to stop instantly. Instant stops, measured with a speedometer at about 55mph, is what I can't explain or understand.

I appreciate your thoughts. Thanks
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bubblehead
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PostPosted: Sun Sep 15, 2013 5:33 pm    Post subject: Reply with quote

Like I said, not a physicist Laughing Good point on the wheel weight/ flywheel effect. An object in motion tends to stay in motion etc. On the other hand, the heavier wheel (and the more drag present)will require more energy to get moving from a stop. And more resistance/traction to rotate. I still think this factors in. Perhaps when the traction/ resistance of the road is replaced with friction between water and tire it is enough to overcome the tire's momentum. Maybe Bill Nye will chime in and shed some light for us. Cool topic regardless.
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pondoras box
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PostPosted: Mon Sep 16, 2013 10:44 am    Post subject: Reply with quote

There are a lot of factors involved here that we dont know. They cant be verified in your case since its after the fact. Remember speed is called velocity but forget about decerleration because a change of velocity is offically accerleration. This is actually important in trying to explain this.

– Vector language – – Corresponding scalar language
Acceleration in the same direction as the velocity. Speeding up.
Acceleration directly opposite to the velocity. Slowing down.
Acceleration at right angles to the velocity. Constant speed.

Acceleration directly opposite to velocity is scientifically refered to as -X acceleration. Friction is a version of the -X acceleration (think about an energy source trying to turn the wheel tire combo backwards but only having enough energy to stop it.

So there has to be an -X acceleration force at play to cause the wheel to stop spinning, mal-adjusted brakes, bearings, low tire pressure, even the toe in / out adjustments being incorrect just to name a few.

Your +Xacceleration is your normal forces encountered while the car is rolling down the road. By the way your rolling resistance,while travelling in straight line, comes from the the internal friction and heat encountered coming from sidewall flex. During normal driving conditions the surface of the tire / contact patch does not move in relation to the road surface therefore no friction or -X acceleration. If this confuses you just take a tire a paint a mark on the sidewall and spot on the pavement and roll it and look for movement, you wont see any.

Now when the tire lifts from the road surface it would continue to spin at or near its current velocity for a period of time unless it was acted upon by an -X acceleration force. In the real world there are constant + and - acceleration forces at play and in a properly adjusted front end / bearing / suspension system the -X would be small enough to not notice a difference in wheel rotational velocity. But in your case it had to be enough to stop the rotation of the tire almost instantly, this could have been due to the condition of ALL of your front end components as well as the depth of the water to even the tempature of the water. The +X as far as the tire is concerned, is when the tire touches down and the passing road will act as a force to accelerate the rotational velocity until it matches the velocity of the road passing under it.

There is another very important factor that would have been at play as well and that is the physics invovled with a rotating mass. Coriolis effect as well as rigidity in space and the fact that any force applied to a rotating mass will result in a reaction 90 degrees out from the force applied. A way to see this in motion is to take a bicycle wheel and tire combo. While holding it in front of you by the axles get someone to spin it for you then try to turn it, it wont turn it will lean, to turn it you need to try to lean it, that why cyclist both bike and motor turn by leaning not actually steering while at speed. So the force of the water acting on the tire to try to stop it will actually try to turn it increasing its coefficient of drag, because it is now sliding in relation to the pavement, the coriolis effect is similar to a figure skater when the spin they pull their arms in closer to accelerate the rate of rotation and hold their arms out to slow down. The simple explaination is the closer the force is applied to the center of a rotating mass the greater the effect of the force. Therefore a dragging brake or wheel bearing will have a much greater effect than a tire that is sliding on wet pavement due to the force being applied closer to the center of its rotational mass.

Before you tell me that you would have felt a dragging brake, maybe not because it wont take much drag to cause this to happen. I have seen people driving in the snow and at low speeds and see the rear wheel, on a front wheel drive vehicle, slide then rotate then start sliding again. Once they get up to speed it rotates fine, they just had to get enough velocity to overcome the existing coeffiencent of drag at the moment.

Hope this helps
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pondoras box
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PostPosted: Mon Sep 16, 2013 10:47 am    Post subject: Reply with quote

By the way bubblehead if your front wheel stops spinning while you are doing a wheely, one of two things is happening here, either you need to repack your hubs or you are really really good at doing wheelies!
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bubblehead
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PostPosted: Mon Sep 16, 2013 10:56 pm    Post subject: Reply with quote

pondoras box wrote:
By the way bubblehead if your front wheel stops spinning while you are doing a wheely, one of two things is happening here, either you need to repack your hubs or you are really really good at doing wheelies!


Right. My example was intentionally simplified for illustrative purposes. And I did say there would still be some momentum at first. My bikes are all in perfect working order. I can only wheelie about thirty feet on a good day so I never see the elevated wheel stop unless I tap the ft brake.
As for your explanation, the last bit about "having enough velocity to overcome coefficient of drag" is pretty much what I was trying to get at. You just managed to do it without sounding like a simpleton! Embarassed And the Coriolis effect is new to me( at least scientifically ). Explanation appreciated.
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pondoras box
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PostPosted: Tue Sep 17, 2013 4:47 am    Post subject: Reply with quote

Just pokin some fun at ya Bubblehead, FYI you can wheelie about 25 feet more than I can. Laughing

And yes i completely understood your explaination of what was going on I just expanded on your post really. No need for this guy Embarassed
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l8sho
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PostPosted: Tue Sep 17, 2013 6:54 am    Post subject: Reply with quote

pondoras: You almost had me! I thought, "maybe this guy knows what he's talking about"......right up to the point where you introduced gyroscopic precession and the assumptions about the condition of the vehicles involved. What has lateral forces on the wheel to do with the subject at hand? Did you just choose to ignore the part about Goodyear engineers experiencing the same phenomenon? And you are assuming that I, and they, and bubblehead, do not know or understand the condition of the vehicles involved? As I said, you ALMOST had me.
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pondoras box
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PostPosted: Tue Sep 17, 2013 9:52 am    Post subject: Reply with quote

Gyroscopic procession is only ONE of many forces at play in this scenario. Didnt say it was or was not the cause in your particular story. Like I mentioned in my opening line we will never be able to actually know what caused your exact cause and effect event. None of it is testable now.

If you toe in was not correct gyroscpic procession would indeed cause the front wheels to try to turn once the encountered friction at the contact patch as the tire is not tracking in a straight line but actually sliding ever so slightly across the pavement diagonally. this effect would be felt 90 degrees prior to the direction of rotation which would be either 6 or 9 oclock as facing the wheel, you figure it out from there what happens when you either oush or pull on a wheel at those locations! Once the wheel turns even slightly the amoung of drag increases both at the contact patch and at the bearing.

Secondly I feel I can probably speak for most everyone driving that they DO NOT know the actual conditions of all of your components. For instance what is the exact coefficient of drag of your front drivers side wheel bearings right now on your current daily driver, how about how much drag / friction is being applied during non braking conditions of the same wheel, how about your current toe in camber, exact air pressure, Should I go on?

We all take good care of our cars and know that the parts are in servicable condition until we experience some warning sign of failure, but none of us know what the exact amount of friction being applied is and I seriouslly doubt the Goodyear engineers took the time to measure half of what I mentioned. Most engineers are subject matter experts on one or two items but that doesnt make them experts in all components of a vehicle.

So your argument that you absolutely KNEW the condition of each and every component in your vehicle's front end at the time of the incident does not carry any credability.

And if this some sort of quiz as to quess the problem then it could a myriad of things! I only listed a few possibilities and I can almost guarantee the problem had to do with friction being enough to cause a significant -X acceleration force to stop the wheel as soon as it left the surface of the road.

Oddly enough though you didnt call B.S. on the coriolis effect which would have the least amount of imput in this situation, just added it to illustrate that there are forces at play that you normally wouldnt even think about.

Bottom line -X acceleration was > the momentum of the rotating mass of the wheel. What caused it will never be fully known in each and every case unless it is done in an insanely controlled evironment.
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l8sho
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PostPosted: Tue Sep 17, 2013 11:19 am    Post subject: Reply with quote

Okay, This is my last input on this. I didn't mention the coriolis effect because I could find no way that it was applicable here. Gyroscopic precession, based on the assumption of poor wheel alignment, could happen I suppose, if the misalignment is pretty extreme.

"So your argument that you absolutely KNEW the condition of each and every component in your vehicle's front end at the time of the incident does not carry any credability."

I DID NOT make that argument. But your assumptions are probably correct. I didn't know my vehicle. In that case, the answer to the initial question is perfectly obvious....the speedometer was broken!
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pondoras box
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PostPosted: Tue Sep 17, 2013 12:39 pm    Post subject: Reply with quote

Quote:
I hesitate to tell this story because in the past when I've told it, some have stopped just short of calling me a liar. If I'm lyin', I'm dyin'.


A freaking joke! Really?

I guess its my fault for being pulled into your stupid BS story about a broken speedometer, my fault for not remembering that the forum is for stories real and fictional.

This had nothing to do with hydroplaning and you probably didnt even know of or even have heard of these principles and laws before you wasted my time.

I dont mind helping people with questions about stuff if I can but I dont like having my time wasted with BS!

I have just added you, my first by the way, to my ignore list!

This is like going to the doctor and complaining of stomach pain and neglecting to tell him you just ate a five pounds of sugar!

What happens when you give a kid a keyboard with no supervision? They grow up to be this guy!
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Looking for anything from Hal Casey Motors out of Hamburg New York, from license plate surrounds to matchbooks.

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1965 11 Window (Zelda)
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Plus a lot of other rusty junk
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l8sho
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PostPosted: Tue Sep 17, 2013 1:52 pm    Post subject: Reply with quote

Pondoras: I guess I was mistaken, that wasn't my last comment. For the record, the original story was the absolute truth, EVERY WORD!! The events happened precisely as they were stated. That includes seeing the Goodyear film. And the speedometer was working fine before and after.

The BS didn't begin until your gratuitous sarcasm toward bubblehead and myself. It wasn't and isn't appreciated! 'Thought I'd give you a taste of your own medicine. I seem to have struck a similar nerve.

Also for the record. I understand what you were saying. But all of the possible factors you suggested don't seem to add up to the final result.

Thank you for adding me to your ignore list.
cd
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