Russ;
RE: "...there was one very lightweight car (that I can identify, from the
front tireprints) that was definitely wandering a lot-- and the back tire
tracks were faint. ..."
I'll wager that car's problem was aerodynamic lift at the rear.
Regards, Neil Tucson, AZ
-----Original Message-----
From: rtmack [mailto:RTMACK@pop3.concentric.net]
Sent: Saturday, December 15, 2001 7:40 PM
To: DrMayf
Cc: land-speed@autox.team.net
Subject: Re: High Speed Traction A few thoughts..
Mayf:
interesting theory, doctor! I think that some were definitely having
traction
problems that were not hydroplaning-- because they were digging-in, not
riding
the surface (not "planing"). However, there was one very lightweight car
(that I
can identify, from the front tireprints) that was definitely wandering a
lot--
and the back tire tracks were faint. I have heard since then that the team
was
having difficulty getting the car to "hook-up" on the "big-end". I wonder
if
they might have been "hydroplaning", as you call it. I think it is possible
that
the cars with not a lot of downforce (relative to area of the footprint of
the
drive tires) may be doing something like that. That might also explain why
the
cars whose drive tires are not "digging trenches" seem to leave tracks that
wander around more-- if they are "hydroplaning", they get batted-around with
every little gust, every little bump.
But that particular car was only in the 250mph range, so tire centrifugal
growth
(shrinking the footprint--??) would not be so much a factor as with the
big-power
guys. As a matter of fact, I think the "shrinking the footprint" part
doesn't
relate to increased hydroplaning tendancy: given the same tread pattern (and
depth), the same vehicle, and the same tire pressure-- a wider tire will
hydroplane (on wet pavement, anyway) quicker than a narrower one. The
narrower
tire tends to "cut-through" the water (or salt??) like a V-bottom boat,
while the
wider tire acts more like a ...well, more like a hydroplane. Note the
difference
in the "rain tires" on the F-1 cars. They are narrower (as well as having
deep
tread).
But the disfiguration of the tire cross section due to centrifugal force--
and/or
the action of the centrifugal force against the salt surface-- could be
contributing to the problem in some other way. Is the centrifugal force
trying
to push the car away from the surface? That is-- is the centrifugal force
of the
tire "countering" (to some degree) the downforce (whether aero, or ballast)
built
into the cars? What do you think about that possibility, Mayf?
Russ
DrMayf wrote:
> Dan, hit your delete key now! Don't want you to get bored..lol
>
> I wonder if the car tires are hydroplaning? That is at high speeds, the
> tires are expanding and becoming pretty rigid from centrifugal force on
the
> outer plys. This makes for a pretty small foot print I suspect. Add to
that
> there is loose salt on the hard stuff. So I think that the tires could
> possible hydroplaning or skating on the loose salt. Why? Well, have you
eve
> driven in sand? Go slow and you sink, but go faster and you skate across.
> Add a bit of moisture and maybe the "hydroplaning" get even more so.
Anyway
> to test this?
>
> just a question...
>
> mayf, the red necked ignorant desert rat in Pahrump...
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