Jump to content
Ultimate Subaru Message Board

Recommended Posts

Is there a new formula for Hydroplaning Speed? I learned from the Brits that it is 9 times the square root of the tire pressure. That is, 54mph for 36psi. This is valid for 1" or more standing water. The tests and subsequent results were a product of the late '50s by Dumlop with bias-ply tires. :burnout:

Share this post


Link to post
Share on other sites

How much water is on the road? What is the tread pattern? What is the tread depth? What is the weight of the car? All of these unknowns make me think that the calculation is far more complex than the one you posted.

 

BTW: I have found that tires start to hydroplane far before the tires reach the end of their life, usually about half way.

Share this post


Link to post
Share on other sites

The tests done by Dunlop were very extensive by any standard. There were variations for extremely wide tires and low normal forces. However, the end result was as I previously stated, no matter how simplistic it may seem. My question is are there NEW formulas that exist that reflect steel belt radials, tread design, etc. By the way, depth of water has to be about 1" or more for one type of hydroplaning. There are two other types but we are just concerned with Dynamic Hydroplaning.

Share this post


Link to post
Share on other sites

I would say there's no simple formula to determine the point at which hydroplaning will occur. It would have to take into account a lot of variables.

Share this post


Link to post
Share on other sites

My "mentor" Leonard Setright, long time journalist in CAR Magazine, once stated that aquaplaning was a function of the tyre pressure, so there is certainly some truth to that formula.

 

He might have been talking about viscoplaning - which is what we actually experience most of the time. Sliding on an ultra thin film of water.

 

I shall dig up the article from my extensive collection, and report back!

Share this post


Link to post
Share on other sites

The formula is

Dynamic Hydroplaning occurs when the speed is at least 8.73 times the square root of the tire pressure.

 

However, some other variables include Viscous hydroplaning and Reverted rubber hydroplaning.

 

But like Legacy777 says, this formula is only one part of the picture...because then I can take like 5000 PSI and never have to worry about hydroplaning. While I'm at it, forget the tires, I'll just run on solid metal rims.

;)

 

P.S. According to the reference that I am using, this formula also applies to radial tires

Share this post


Link to post
Share on other sites
Originally posted by Strakes

...because then I can take like 5000 PSI and never have to worry about hydroplaning. While I'm at it, forget the tires, I'll just run on solid metal rims.

 

that's what trains do. It'll work.

Share this post


Link to post
Share on other sites

FWIW, Consumer Reports has an article on hydrplaninng and worn tires.

 

The faster you drive, the greater the risk of hydroplaning, since higher speeds allow less time for water to escape through the tread grooves. Shallower tread worsens that situation by allowing more water to stay beneath the tire. Our half-tread tires began to skim over the water’s surface at as slow as 40 mph in our hydroplane test, about 3 to 4 mph slower than the full-tread tires. As the chart in All-season-tire wear shows, that represents a nearly 8 percent drop in hydroplaning resistance compared with the same model tires when new.

 

This was very noticable on my Michelin X Ones ('97 OB wagon), which I just replaced with 60K miles despite significant tread remaining.

These tires when new were the best rain tires I'd ever had. But by last month I was hydroplaning at 65+ in heavy rain. Inflation pressure was 35 psi cold.

 

I replaced them with Michelin HydroEdge tires last week. With about 300 miles use they are noticalbly quieter and turn-in better than the X-Ones. It has not rained since I bought them, but by the end of the week I should have a rain report as well - maybe even snow.

Share this post


Link to post
Share on other sites

These Gemans on the autobahn over here must have the formula. On my way to the airport this morning, it was raining and extremely dark, and I was being passed by people going over a hundred mph.

 

Or, maybe they use the formula that has a multiplier of stupidity in it...

 

My formula is: If the road is pretty wet, slow down!

Share this post


Link to post
Share on other sites

Indeed, I limit myself to 100mph on wet Autobahns. If the stretch is de-restricted of course!

 

Have you noticed how many stretches have "110 bei nasse" signs? "70mph in the wet"

 

Watch out, the cops get really angry if you ignore these signs! Over 30km/h above the limit and your license is in serious danger.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

×