Contour Enthusiasts Group Archives Forums General General Theoretical Tire Question (EdwardC, I need a physics lesson here)

Suppose you are buying tires for your Contour and you were concerned about hydroplaning. Given the same tire in two different widths, assuming the same weight of the car, identical tire pressures, identical tread patters (except for the width of course) which would resist hydroplaning better, the wider or narrower tire, and why.

This sounds like a problem for EdwardC

TB

Hydroplaning occurs when water, which is non compressable, cannot be "squeegeed" out from under the moving tire. The non-compressible water will act like a more viscous solid (ice?) and cause the tire to skid. Deep, wide grooves in a tire, along with grooves that go sideways funnel water away and help prevent hydroplaning.

Assuming that both tires had similar tread, I think that the narrower tire would have "higher force per unit area" with the same weight vehicle, and deliver more force to displace the water. Bicycles probably would never hydroplane.

Buy good M&S rated tires with cross tread, and the wider tire should be fine. Good Luck.

Al :rolleyes:

This is what I thought too, however:

http://www.smartmotorist.com/rai/rai.htm

If you check the science of hydroplaning in this text, it says just the opposite.

In fact, go to this site, and it backs that up with a mathematical rule of thumb http://www.msgroup.org/TIP035.html

So, while your answer makes sense to me, and this was how I was thinking. I now wonder if what we believe is true at all.

EdwardC, we need the physics, but in laymans terms, please!

TB

That's true.. sorta. Let's take this to extremes to see what I think is much more important.

If you had a bicycle tire on your car.. basically 1" wide, you'd never for any reasonable speed (sub 150mph) hydroplane. The simple weight of the car plus the fact that the tire will work like a knife will stop that from happening.

If you were to put balloons.. say 14" wide on your car, you'll hydro-plane that much faster. Which seemingly contradicts that quote.

You'll push that much more water in front of your tire to hydroplane with, becaue the contact patch's difference in cross sectional area creates less PSI for the water to carry the car.

Say the car weighs 4000 lbs. for arguments sake. If your contact patch is say 25 square inches, you have 4 of them(tires ya know). You'd need to have 40psi of water underneath your tires to support your car.

If your contact patch is say half that, you'd need 80psi of water underneath your tires to support the car. The chances of accumulating that pressure under the car with a narrower.. ie smaller contact patch is harder to accomplish and therefore takes a progressively higher speed to create that psi.

However if the contact patch was like a paddle, it would perform exactly like the bicycle wheel, cutting through the water instead. Provided that breaks in the tread are provided for the water to pass through. You could just as easily build up as much of a wave front before the tire with a wide but short patch that may create enough water to supply the necessary psi, but it's harder to do so it will plane before the bicycle tire but a lot more speed is required than the a wide and long patch area.

The area of the contact patch is what's key here, not really the width.

Ok,

I understand the area thing. So, give two tires of like construction, same tire pressure, the area of the contact patch "should" be the same. But the length and width values would be different.

And that was in my original question. Perhaps my assumption that the writers in these web articles are also keeping other variables the same and only varying the width of the tire, and hence the width of the contact patch, is incorrect.

But what really happens?

TB

What if you had tires 5 feet wide that were siped and grooved correctly to remove water from under them? You probably would never be able to hydroplane, I'm guessing due to the large contact patch. What if you drive over a hole in the road when wet say going bout 50 on bicycle tires? You lose it, but not if your on 5 feet wide tires. Like Pontaic says "wider is better."

I figure the larger the patch is the more water is needed to be removed from under the tire.

Well we can always go back to the Double tire like trucks have. There was (maybe still is) a company in europe making rims like that for high performance cars. Basically because this guy was getting sick of being passed by VW's on the Autobahn whenever it was raining. He made the dualie rim and the tires basically 'cut' through the water like a bycicle tire.

For all practical reasons, the wider the tire, the more likely you are to hydroplane.

Basically the wider the tire the better (if they both had the same treads). We just covered this in Drivers class last week. You would want more surface on the road as opposed to less - But the width doesn't always count, it depends on the tread as well.

Bump, I'm hoping our resident physics expert EdwardC would chime in here.

Maybe I should post a new topic on Off Topic.

"Fundamentalist Christians claim Hydroplaning is the work of the Anti-Christ"

Perhaps that would get his attention

TB