2nd Gen Non-Engine/Transmission Hydroplaning-- what is it, what causes it, how can I avoid it?

[Hohn]

First of all, let me say that I am posting this in hopes that I don’t insult anyone’s intelligence. I have just read a thread where someone was talking about tall tires vs skinny tires in relation to hydroplaning, and I found that there is some misinformation out there on the exact phenomenon. If I do a good job writing this, maybe they will let me write for the TDR mag? OK, maybe not…



Hydroplaning is what happens when a tire fails to contact the road surface because it is “riding” on a wedge of water on the road. Imagine the difference between your buddy’s bass boat trolling along THROUGH the water, versus when that monster 150HP outboard has you skimming ON TOP of the water. The skimming is hydroplaning, and the variables we will discuss all play a factor in both tire hydroplaning and the bass boat scenario. Since hydroplaning occurs specifically on the tire’s contact patch, let’s look at the factors that affect traction on a wet road:



1) Width of tires -- more accurately, the surface area of the contact patch (to some extent tire height plays a role as well, since a taller tire has a bigger contact patch for a given width)

2) Axle weight—the FORCE acting on the surface area of the contact patch

3) Depth of water on the road—this determines the VOLUME of water that the tires must displace to contact the road.

4) Viscosity of the fluid displaced—i. e. a “thinner” fluid pumps easier, and therefore would be less likely to hydroplane. We assume we are talking only about water, so let’s consider this one constant.

5) Speed of vehicle—This determines the TIME available to displace the water in the contact patch.



In order for a tire to have traction on a wet road (primarily standing water) it has to first displace the water between the contact patch and the road. Because water is a viscous fluid, it tends to resist this displacement. The more water you have, the more resistance. In fact there are really only three factors that play a role in hydroplaning: pressure on the contact patch (weight on each tire divided by surface area of contact patch), the volume of water that must be displaced, and the time available to displace that water. In fact, we could write it as a formula:



(Pressure * Time)/volume= resistance to hydroplaning.



We can draw from this formula a number of conclusions:

1) the deeper the water is, the more likely I am to hydroplane (more water volume)

2) The more pressure on the contact patch, the LESS likely hydroplaning is.

3) The more time available to displace the water, the less likely hydroplaning is. (Slow down!)



This confirms what you already know—tall skinny tires tend to hydroplane less than fat tires. We can see two reasons for this. First, the wider tire has to displace MORE water. Second, the wider contact patch has LESS pressure on it since weight has stayed the same (P=F/A) This is a “double whammy”.



This isn’t the only way to decrease the chances of hydroplaning. The formula tells us we can drive a heavier vehicle or slow down. But if we increase the efficiency with which the tire displaces water, then the TIME required to displace it decreases, and we are less likely to plane out. This allows us to either decrease vehicle weight or increase speed safely as a result.



Finally, the SHAPE of the contact patch has a role in hydroplaning. For a given area, say 15 square inches, a longer, narrower contact patch is better than a short wide one. Why? Because the majority of the water displacement is done by the leading edge of the patch only (picture our bass boat and its bow). The rest of the contact patch gets a “free ride” along behind the leading edge that already displaced the water. Thus, a narrower leading edge slices better through the wedge of water.



Go ahead and run the biggest tires you wish. Just remember the physics that is taking place at your tires’ contact patches and SLOW DOWN!! (or add a bunch of weight, or run narrow tires, or……. .



HOHN

 

[Diesel Freak]

sounds good to me

 

[benhall]

That floats my boat. :-laf



I can't wait until someone brings up black ice.



Ben

 

[Hohn]

Black Ice?

So you are saying you want to here my spiel on the formation of the crystalline structure of ice under various conditions?



Ha! I won't torture you all with THAT one>>>>>>



HOHN

 

[Diesel Freak]

Re: Black Ice?

Originally posted by Hohn

So you are saying you want to here my spiel on the formation of the crystalline structure of ice under various conditions?



Ha! I won't torture you all with THAT one>>>>>>



HOHN

awwww come on... go for it!

 

[TPCDrafting]

HOHN, I read many of your posts and although I don't always agree 100%, I could think of at least a few regular articals in the mag that could be replaced by your writing.



BTW, I do agree 100% with this one. Tim

 

[jerryrigg]

Hohn... . Excellent write up, but if I may be so bold to add one item



Tread Design and wear also play a key role in the ability of a tire to displace the water. Aggressive mud tires and special designed water tires (aquatreads) are superior in water due to the deep channels allowing more water to pass under/through the tire without the tire riding up on the water surface. Of course the more miles and less tread a tire has also leads to a greater risk of hydroplaning because the "channels" have reduced in depth. These tires also work on the principle of the "contact patch" and "ground pressure" for water displacement. The tires may have a contact width of 9" but you must subtract approx 1. 5-3 inches of that for the channels (depending on the tire) in the tire thus the contact patch is only 6-7. 5 inches this inturn increase the contact pressure in psi allowing the tire to penetrate the water easier. But once again we are back to tire wear, the deeper tread allows more water to flow through the narrower contact patch.



-Matt

 

[Hohn]

tread design in hydroplaning

Matt:

I didn't mention it specifically, but this is what I meant when I talked about the efficiency with which a tire displaces water. That infers the "rain tire" designs like the Aquatred and others.



FWIW, I don't think that a mud tire is necessarily all that good in the rain, though you are right that it does resist hydroplaning, which is what we are discussing here. I find a mud tire to only be good in the rain if the bigger lugs are heavily siped. Yes, they wear fast, but the extra traction is your reward.



By the way, I have a 1997 Nissan Maxima, and I have decided to always put on the stickiest, Z rated (or higher ) rubber that I can find. Yes, the tires are more expensive. Yes, you might not get 20K miles out of them. BUT if either myself or my wife find ourselves in a situation were maximum traction means the difference between an accident and avoidance, then all the tire $$ in the world would STILL be cheaper.



I also gave up replacing tires as sets of four on a FWD car. I replace them as pairs and only rotate side to side. Since a FWD car does ALL its acceleration and 80% of its braking with jus the front, I figure you want the stickiest tires you can get out front. Also, since almost every FWD car tends to understeer (they're front heavy), you can even out the handling by getting a little less traction in the back relative to the front. So I put all season touring rubber on the back, and gumballs up front.



I have my eyes on the Toyo Proxes T1-S. That has to be the coolest HP tire I have ever seen.....



TPC: Thanks for reading the writings. I am going to lay off the political/religious stuff and reserve those thoughts for when people ask. I don't want someone ignoring my tech posts because I ticked them off with a pol post.



HOHN

 

[Steve Campbell]

This doesn't quite fit....

but I will talk about "loosing control of the vehicle" so I ask for some leeway.



If you are driving on "white" roads (covered with snow) and the tread of the oncoming vehicles appears "white" the traction is "pretty good". Temperatures are cold enough for the snow to "stick" to your tires. (Think of the tongue stuck to the metal bar in the winter "problem". ) In this case, it is a good thing.



If you are driving on "white" roads and the oncoming vehicles treads are "black" (duh-they come from the factory that way), then the traction is "poor". It is warm enough that snow won't stick, thus the traction suffers. Time to slow down, which won't improve your traction, only the distance you will slide if you loose control.



Come to think of it..... maybe there is a form of hydroplaning involved (a thin layer of water created between the "warmer" tire and the snow. )

 

[Hohn]

snowplaning?

TO some extent, you are right, Steve. The pressure of a rolling tire on snow lower the freezing point, causing the snow to melt. This is why roads get so icy where tire tracks are: the traffic melts the snow from tires exerting pressure, and then it refreezes almost instantly.



There IS a thin layer of water there, but it's not TECHNICALLY hydroplaning as we generally think of it. The presence of a thin layer of water in the contact patch on snowy roads is why you see winter tires have a BUNCH of sipes, and they are usually a multicell ruber compound (little air bubbles in it).



This is why you have a lot more traction in bitter cold than when it's between 25 and 40 degrees. When it's really cold, it's too cold for your tires to melt the snow, so you don't have that layer of water.



Just to be clear: it's not the HEAT from the tires that melts the snow as you drive over it, it's the PRESSURE caused by the weight of your car... ...



HOHN

 

[CFAR]

2 things,



1. Tires designed to have long tread life tend to have more rubber on the road, skinny or not, hence more chance of skiing.



So to determine the "resistance to hydro... " you would need to calculate the actual amount of rubber on the road and don't forget to factor in groove volume(water escape route), as we all know the large flat stone skips better than the round one.



couldn't agree with you more on speed



2. Snow tires, well good snow tires(or so I've read), are designed to pick up and hold snow, snow on snow has much better traction than rubber on snow.



probably should have kept my keyboard shut



If anyone wants me to write any articles, sorry I can't, I'm already writing for the speed readin thing.



Woody

 

[dan_gilson]

Weight on the tire is much less a factor than you think. You can still hydroplane a plane landing with a gross of . 5M#'s.

on just a few tire with a relative small contact patch. So the PSI per size of patch is whay up there.



The key is being able to channel water out. And this is a factor of the speed you are traveling.



The best place to find the research for this is planes. The did the initial research because they could not further reduce the speed of landing (otherwise stall).



In a car, the best thing to do is SLOW down. Thereby giving the tire more time to channel the water out.



All tires designs are a compromise. They bias one feature over another. There is no perfect tire. Having good tire with deep thread that channels water out is essential.



Longer and narrower means bigger diameter. Can anyone say big truck wheels and tires. There are some other advantages with this. The tire rotates less frequently. Which means there is less contact per a given mile. Less contact per given mile means less heat because of less contact and sidewall flex.



Good write up!