Hydroplaning, was: Re: I have seen 225/50-15's on a 4kq

["Janet Scruggs" <scruggs@mbay.net>]

Now that the topic of hydroplaning has been broached, I'd like make it more
complicated.  Dave Eaton, and others, have made the case that what we are
dealing with is a 'weight per square unit' relationship and I agree that it
feels 'right' and there is probably no need to investigate further... but.
Years ago the trucking industry studied this issue and found that there is a
direct relationship between tire pressure and ability to resist
hydroplaning.  Further they found that the loading of a tire was not as
significant a factor as the tire pressure.  I'm sure that on a graph of
these two influences the loading and pressure lines will cross somewhere,
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.

I offer the explanation that with increased pressure the tire will deflect
less as it rolls into a non-solid surface, like water, effectively 'cutting
through' the water layer to a solid surface more effectively than a tire
having less pressure.  Examining the extremes seem to support this:  Imagine
two tires of the same width and loading one being inflated to 10psi and the
other made of aluminum (sorry Phil and Jim... aluminium).  Now roll them at
speed through your imaginary water trough.  Seems to me that the stiffer of
the two should 'cut through' the water and resist riding on top of the water
film.  Comments?

A word about how we, the qlist, go about explaining the things we experience
with our automobiles.  The very most helpful analogy for solving any problem
is that of the blind men attempting to describe the elephant by each
relating what they touch.  When the problem is large, this is an effective
way of addressing it.... divide the responsibility then assemble the
individual reports.  Problems arise when any of the participants deny the
any of the other reports... and the shouting begins.  Sound familiar?  The
group goal should be toward integrating the experience of each of the others
and assembling a total picture of the elephant.

So, I offer the above explanation of the influences of hydroplaning in the
spirit of one of the blind troops reporting his findings.  I understand that
I do not have the total picture but hope that my report will help us better
understand the that total picture.  My most fervent hope is that chance has
allowed me to place my hand on a part of that elephant that contributes to a
solution and not, as I often fear, placed my hand on a part of the elephant
that one should not be touching.  Just in case, I'm going to go wash my
hands... and inflate my tires.

Regards, Gross Scruggs