RE: Hydroplaning

["Graydon D. Stuckey" <graydon@apollo.kettering.edu>]

On Wed, 25 Nov 1998, Geoff Jenkins wrote:

> Been thinking about this... I agree in re: the effect of pressure, but _how_
> do you separate pressure from area? Assuming vehicle mass is identical, as
> you lower the pressure, surely don't you soften and flatten the tire, so
> that the force downwards remains constant?

I tihnk that the pressure is merely the factor that produces the feature 
that improves hydroplaning.   Its the hardness of the tire that affects 
hydroplaning.  Sinceair is compressible and water is not, you need alot 
of pressure to reduce how much the air compresses when it hits water.  If 
it compresses very little (extremely high air pressure) then the shape of 
the tire stays relatively constant, and then it becomes a fight for 
space.  Once this happens, although water is not compressible, it does 
move, so eventually it gets out of the way, and you do not hydroplane.  
If there is enough water though, the force required to move it out of the 
way is more than the tire can muster, so you go straight.

> > but I've no idea where.  I do know that the front tires on semis are
> > typically inflated to around 85psi and all the rest to around 65psi.

So Gross, are we to run out and change our front tire pressures to 85 
psi?  Its raining here...  :-)  Just joking.

Later,
Graydon D. Stuckey
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