2nd Gen Non-Engine/Transmission Holy hydro planing, Batman!

[Bova]

All the differant tire brands that I have run, the best wet weather tire by far is the Bridgestone dueler A/T Revo. This tire is unbelievable in the rain. Thats the main thing I look for when buying a tire. I don't try to save money on tires or brakes, only the best is used. The few hundred extra dollars is money in the bank compared to sliding into a family of five in the rain with those bargain tires.



F-1 cars run 13" rain tires



1100pds



950hp



2. 5g's



200mph

 

[RowJ]

A lot of interesting ideas and logical arguments have been stated.

As a former corporate pilot I learned 20 tears ago about the above mentioned formula - 9 times the square root of your tire pressure! The way I learned it was different planes have different sized tires, different weights and even some different tread designs BUT none of these things make any difference.

I know it's counter intuitive and seems like different factors should effect hydroplaning differently, but I have always used this formula for any car or truck I owned and done enough informal testing to prove it accurate for me.

By the way a tire will hyrdoplane with as little as 1/100th of a inch of water on the road. (Just learned this on a national driving test).

I memorize that number and stay away from that speed when roads are wet!

 

[Hohn]

I got this via PM, and I think it's relevant to our discussion here:

I read your explanation regarding hydroplaning. I think it's possible that you have made an error.



I haven't studied tire design, but I have studied pavement design. In our pavement design classes the pressure on the pavement from a vehicle's tire was always assumed to equal the tire pressure. This is true if the tire sidewalls carry no load. Of course they do carry a small amount, but it can be ignored in most cases.



The result of the above assumption is that if vehicle weight is increased, the tire will flatten out enough to create a contact patch large enough to carry the new load. Pressure on the pavement will still equal tire pressure. The new, larger contact patch on the pavement will negate any advantages gained from the heavier vehicle.



The speed at which a tire will hydroplane is a function of many variables, but I doubt that weight is one of them.



I have noticed that the formulas used to calculate hydroplaning speed do not account for any tread pattern on the tire. This would lead me to believe that tread pattern doesn't matter, but I doubt that this is true, since tire designers have created some tread patterns that do better than others on wet pavement.



I'd be interested in your sources for the discussion on weight.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~



I don't have any sources for my info, just my own fallible reasoning.



Consider a bass boat planing on top of the water, or idling through it slowly. When the boat is idling throgh the water, it must DISPLACE that water in order to move there (since physics tells us that two things cannot occupy the same space). If you add weight to the boat, it sits lower in the water, thus requiring it to displace more water.

Now when the boat is "on plane" it isn't displacing the water anymore. If the boat is moving FASTER than the water can be displaced, it will rise up out of the water and "plane out". Because the water has viscosity, it takes time for it to be displaced. IF the boat is moving faster than the water can, it will plane out.

Now what if you add weight to the boat? Well, in order to plane out, the force of water against the hull must be greater than the force that holds the boat down in the water-- gravity. So when we add weight, we increase the amount of force that the water must generate in order to overcome gravity.



This is why weight matters. All else being equal, a heavier wheel (one with more weight on it) will tend to plow through the water instead of hyroplane.

In our pavement design classes the pressure on the pavement from a vehicle's tire was always assumed to equal the tire pressure. This is true if the tire sidewalls carry no load. Of course they do carry a small amount, but it can be ignored in most cases.

This is a popular myth-- that the AIR in a tire carries the weight. You CANNOT take the area of the contact patches and multiply it by tire pressure to find out how much load is on the tires. This is because the TIRES carry the weight-- the air is there to ensure rigidity of the tire.



Consider two tires- one from a bicycle, the other from a big rig trailer. Both are inflated to 70psi. The bike tire carries 100 pounds at 70 psi when the tire is 30mm wide. That means that the contact patch is about one inch wide, and probably over an inch long. It seems to prove that the air is supporting the load, right?

What about the truck tire (a 275/80R22. 5 LRH Michelin XZA2), which is 10. 9 inches inches wide and supports 8300 pounds with only 70psi? If the "air" theory was true, the contact patch would have to be over 118 Square inches. With a width of 11 inches, the contact patch would have to be over 10 inches long. Well, that seems reasonable enough.

But what about the tires on my truck? At the maximum rated pressure of 80psi, the weight limit is ~3400 lbs per tire. So, the air theory gives us 42. 5 sq inches to support the weight. The tire is (265/25=)10. 6 inches wide. So our contact patch is only 4 inches tall? Not quite.



What about when I air down for off-roading? My tires will handle 10psi up front. To support my FAW, I would have to have over 200 square inches of contact patch! Given the tire width of 10. 6 inches, that means the contact patch would have to be almost 20 inches long!! That's not going to happen on a 31" tire.



In short, don't be fooled about tire pressure and hydroplaning. Weight matters when it comes to hydroplaning. And your TIRES support the load, not the the air within them. The air just makes them more rigid so they can do their job.



Justin

 

[rashwor]

Huh?

I should have taken physics. This is interesting.

 

[fkovalski]

I should have taken physics. This is interesting.

... and, fluid dynamics!Oo.

 

[Hohn]

More that I got from PM:

~~~~~~~~~~~~~~~~~~

Justin,



Your logic regarding what supports the load on a tire is incorrect. I don't remember enough of my engineering to run through the math, although I could probably muddle along, given enough time.



The air in the tire is exactly what supports the weight of the vehicle. The ONLY load that is not carried by the air is carried by the tire sidewalls. With most tires, this amount is insignificant compared to the total load. This information was not derived from a textbook, but rather proved in my civil engineering classes. The goal of this exercise was to simplify pavement design by allowing the assumption that tire pressure equals pressure on the pavement. Within engineering tolerances, this is true.



For an intuitive way to understand this, picture a wheel with a tire mounted on it, not installed on a vehicle. Remove the valve stem from the tire. Now, how much weight will that tire support before it goes flat. Compare that amount of weight with the total load that the tire carries with air in it.



Some tires have much stiffer sidewalls than others, and some of these tires may carry several hundred pounds before they collapse in my scenario above. These tires, however, are usually used in applications that involve much higher total loads. The contribution that the sidewall makes to carrying the total load is ignored in pavement design for this reason.



This is off the subject of hydroplaning, however. As I, and others have stated, hydroplaning is a complicated subject. Calculations involving hydroplaning speed ususally start and end with tire pressure, but the other factors I mentioned elsewhere are also involved.



By the way, the main reason that truck tires hydroplane at higher speeds than automobile tires is because the truck tires are carrying much higher pressure, not because there is more weight on the tire. I submit that a high pressure (150psi) bicycle tire will hydroplane at an even higher speed than an 80 psi truck tire. Given the limitations on bicycle speed, it is almost impossible to get a 150 psi bicycle tire to hydroplane. That bicycle isn't carrying nearly the weight that a truck is.



You certainly have my permission to post all of this if you want to, but it was not my goal to start an argument, either public or private.

~~~END~~~

 

[Hohn]

My reply

First, let me talk about the tire pressure/support points. Then I will talk about the hydroplaning.



It appears to me that basic hydraulic theory is the angle you are taking here. Namely, that if Pressure= Force*Area, then our version would be that TirePressure= Force (of gravity)*Area (of contact patch). In other words, Tire Pressure= Weight* area of contact patch.

Since there is “an equal and opposite reaction” for every action, we can say that the force of the weight on the wheel has to be equal to the force inside the tire pushing against the road to support that weight.

But there are TWO components to this force. First is tire pressure. Second is the tire’s rigidity, both from sidewall stiffness and from the elasticity of the tread surface that must deflect when it meets the road. .

Clearly, you are overlooking the importance of tire rigidity. You CAN disregard this for your purposes of road design (and I am not even talking about road design at all), but you CANNOT disregard this when talking about how tires support a load. If air pressure was all-important, then how are run-flat tires possible?? It’s simple: they are rigid enough to where they don’t need the support of the air pressure at their load.

So you can kind of see why I was saying that the air pressure is secondary—it serves only to add rigidity to the tire. Air pressure and tire rigidity work together. But you can’t ignore rigidity because the air pressure affects how rigid the tire would be!!

Now, it’s possible for me to make a tire that’s SO rigid that it will support a couple hundred pounds with no air pressure at all. Obviously, the basic hydraulic theory approach falls apart here, since with ZERO air pressure, you couldn’t support any weight (if you disregard tire rigidity). So what do you do when you have a certain size contact patch with ZERO air pressure? Certainly, the math falls apart on that one.

Furthermore, the basic hydraulic method (weight=tire pressure*contact patch area) is ONLY accurate when tire rigidity is zero. You would have to have a tire so soft that it would collapse under its own weight. That tire is not used in any application.

So we have learned two things: we can’t separate air pressure from tire rigidity, and air pressure is secondary to rigidity, since the tire gets its rigidity from the air pressure. It’s a one way street, since you can have a sufficiently rigid tire with no air, but you cannot have air in the tire without it affecting the rigidity.



Now, onto the comments abut hydroplaning... ... .



Justin

 

[RowJ]

Hydroplaning

This subject may be as bad as asking which oil is best!!!

 

[fkovalski]

This subject may be as bad as asking which oil is best!!!

:-laf



That's funny! Alas, it is interesting as a disscussion topic. I never thought it would get as indepth as this when I posted the original comment. But, it has been educational for me. I must re- iterate: this is why I joined the TDR. Regaurdless of one's political persuasion or opinon of "bikini of the day," we can all agree on a fantastic disscussion about factors that affect our trucks. Cheers to all! -fjk.

 

[jwinnie]

Great thread!!!

Just thought I'd throw this into the mix: Click here for good info

 

[DaveN]

The good news is....

that at least you were able to see when you were hydroplaning, I hear you have some awesome custom wiper springs...



My 0. 02 on the hydroplaning issue (from a mechanical engineer, granted I was drunk for most of my college career, but... . )



1. Weight is a factor. More weight, less hydroplaning. Based on physics. more weight equals a higher pressure on the tire/road surface, this will become relevant after reading point #2.



2. Hydroplaning is caused by water not being able to escape from under the tire tread fast enough. It then builds hydrodynamic (or hydraulic, depening on your personal beliefs) pressure. If this pressure exceeds the pressure exerted by the truck/tire onto the road, then you're riding on a 7000 pound mass missle with no control. WHEEEEEE Based on physics.



3. My personal opinion about automotive tire pressure and hydroplaning is that tire pressure is mostly irrelevant. The only variable there is contact area, which could increase or decrease the pressure. In most cases if the tire is aired up enough to support the vehicle properly, the contact area is relatively close in size with small differences in air pressure.



4. Aircraft may be different. Their tires and tread are of a different configuration, and the aircraft discussion may not apply to automotive. Not to mention they are landing/taking off at 100+ MPH.



5. Bottom line, if you find yourself hydroplaning often, then a. check your tire tread. If you're getting low on tread then get new tires, don't be like my dad and wait until you see steel. That's asking for trouble, or b. get new tires with a more open tread design or c. slow down.

 

[DaveN]

Read a little further....

Air pressure does support the load that a tire carries.



You cannot calculate the contact pressure by measuring air pressure.



Contact pressure is: weight/area. Different tires will have a different contact area at different weights/pressures. So it's determined on a case by case basis based upon the tire design.



Sidewalls don't carry load. I've yet to see an automotive tire that could hold vehicular weight without air. The only expection to this was that my kids tricycle could, but it was holding up about 3 pounds of bike. Sidewalls are for side to side rigidity to keep the tire from rolling off the bead, they are for connecting the tread portion of the tire to the wheel, and they are used for holding air, and collecting sharp objects that wreck your tires. They are also used by the tire companies to put information and free advertising on.



OK another bit of 0. 02, I think I'm up to four cents now. This conversation is getting expensive!

 

[fkovalski]

that at least you were able to see when you were hydroplaning, I hear you have some awesome custom wiper springs...

Yes, Dave - It is working great! I have yet to put on the winter blades, but last winter was obsticle free and expect no less this year. Thanks again for letting me be a "guinea pig" for your experimental wiper arm springs!



As far as the hydoplaning issue and comment #5 of your first post- The tires I have are new (less than 1000 miles) so I don't think that lack of tread is a problem. I'll have to be more aware of the trucks handling characteristics and slow down in heavy downpour stuations. -fjk

 

[OL RATLR]

Hydro Planing

Bottom line Gentlemen! When there is that much water on Road slow down

and you want have near the problem Hydroplaning.

 

[fkovalski]

Do not use cruise control

How ironic that I recieved this e-mail from a friend related to the topic:

*****************



Energy is neither created or destroyed, it just changes form!







Please Read!!!!!







This could save your life... please read



A 36 year old female had an accident several weeks



ago, and totaled her car.



A resident of Kilgore, Texas, she was traveling,



between Gladewater &Kilgore. It was raining,



though not excessive, when her car suddenly,



began to hydroplane and literally flew through the



air.



She was not seriously injured but very stunned,



at the sudden occurrence!



When she explained to the highway patrolman,



what had happened he told her something,



that every driver should know -



NEVER DRIVE IN THE RAIN,



WITH YOUR CRUISE CONTROL ON.



She had thought she was being cautious,



by setting the cruise control and maintaining,



a safe consistent speed in the rain.



But the highway patrolman told her,



that if the cruise control is on,



and your car begins to hydroplane,



when your tires loose contact with the pavement,



your car will accelerate to a higher rate of speed,



and you take off like an airplane. .



She told the patrolman that was exactly what had



occurred.







We all know you have little or no control over a



car, when it begins to hydroplane.



You are at the mercy of the Good Lord.



The highway patrol estimated her car was actually,



traveling through the air at 10 to 15 miles per



hour faster than the speed set on the cruise control.







The patrolman said this warning should be listed,



on the drivers seat sun-visor - NEVER USE THE CRUISE



CONTROL,



WHEN THE PAVEMENT IS WET OR ICY,



along with the airbag warning.







We tell our teenagers to set the cruise control,



and drive a safe speed.



But we don't tell them to use the cruise control,



only when the pavement is dry.







The only person the accident victim found,



who knew this (besides the patrolman),



was a man who had had a similar accident,



totaled his car and sustained severe injuries.







If you send this to 15 people and only one of them,



doesn't know about this,



then it was all worth it.



You might have saved a life