It seems to me that the easiest way to measure coefficient of friction of
actual tires on salt is with a good accelerometer. Maximum acceleration
(just before tire spin) could then be used to calculate friction from the
expression G accel. = friction (%weight on driving wheels).
Some old literature gives a value of around 0.5 without saying what the tire
width is, but presumably the usual 3" Bonny tire by Firestone of those days.
The electrical devices measuring resistivity or conductivity would measure
the most conductive layer, but is that the water on top, or the solid
(saturated) salt below?
We have established that the fastest runs occur when rolling resistance is
lowest. Couldn't this just be a function of how warmed up the wheel
bearings and rear end gears are? You do see astute tuners heating their
rear ends in the morning with a torch or running the engine and turning the
wheels in gear with the rear jacked up.
Dave the Hayseed
----- Original Message -----
From: DrMayf <drmayf@teknett.com>
To: Dave Dahlgren <ddahlgren@snet.net>; Marge and/or Dave Thomssen
<mdthom@radiks.net>
Cc: Land-speed Racers <land-speed@autox.team.net>
Sent: Thursday, June 28, 2001 10:50 AM
Subject: Re: Air density and rolling resistance.
Dave,
I'll do a bit of thinking on this. But there are several problems I can
thnkof right off the bat, that will need to be ovecome. One is the rubber
compound being used under the skid. Soft or hard would play a big role in
determining the coefficient of friction. Then there is the problem of loose
salt under the skid, a condition most likely on the actual race surface.
These can be estimated tho, maybe...HArdness, what would we relate that to?
Take for example, old concrete vs new concrete...how to tell the difference
there and what effect it has? I am in the dark here with zero knowledge on
the subject. For me, traction is a weight thing (normal force) but what I
would like to investigate is rolling resistance. If I had a data system like
yours and my car with the front struts and trailing link, I would find a way
to put strain gages on that link so that I could convert the wheel rolling
force to strain and load. I would then vary air pressure in the tire and
make several runs, do that for as many conditions as I could think of, and
maybe even different tires to get a set of numbers that could be related to
rolling resistance. Or build a "trailer" with a load cell between the tow
and it to measure rolling resistance. Could add and subtract weight to
change the parameters. Lots os stuff. Maybe I'll look into it...
mayf, the really red necked ignorant desert rat
Subject: Re: Air density and rolling resistance.
. Ok Mayf how do we easily measure the
> available traction and hardness. I have 2 ideas. For traction a small
weighted
> sled with rubber on the bottom and a pull scale. measure the breakaway and
> sustaining force to move it along the salt. Then a round metal ball may a
few
> pounds in weight dropped from a certain height and measure the diameter of
the
> imprint to measure hardness.. Could also measure the temperature and I am
sure
> someone would have a way to measure the moisture content at the surface.
With
> all the traction issues at Bonneville it really has to come down to where
the
> rubber meets the road for a lot of people
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