Doing the math (for vehicle weight)

[Joe Yakubik <75363.2524@compuserve.com>]

91  200 TQW weighs in at a whopping 3563 lbs.

This is, of course, only as accurate as those four bathroom scales I parked it
on and includes the five inches of snow on the roof.

Actually you can get a ballpark figure for the weight of your car, but you do
have to....."DO THE MATH"

The Gross Vehicle Weight Rating is posted on the inside of the drivers door.
This number is supposed to be the maximum the vehicle can weigh.  It includes
the max. load plus a full fuel tank, oil and coolant.  The max. load is the
estimated weight of passengers and luggage.  This is the max number of seats x
150 lbs plus luggage.  Or the easier way to find "max. load" is to look in your
fuel filler door and read where it says "max load".  Subtract this and the rest
of the values from GVWR and you get a weight, or don't subtract the oil, coolant
and gas, because those are always in the car (or should be!).

My example:  '91 200  TQW with the proverbial "loaded" - power leather seats,
A/C, roof rack, etc.

fuel tank 78 liters/ density of gasoline 0.67 kg/liter   (20.6 gal@5.6 lbs/gal)
= 115 lbs
oil 4.5 liters / density of oil 0.9 kg/liter (5.0 qts@2.1 lbs/qt) = 10.5 lbs
coolant (50/50 alcohol/water)  8.0 liter @ .9 kg/l  (2.1 gal@7.54 lbs/gal) =
16.5 lbs

total "liquid weight" = 142 lbs

GVWR from drivers door = 4805 lbs
max load from fuel filler door = 1100 lbs
Liquids = 142

 car "dry weight" = 3563 lbs

There are some minor inconsistencies in the metric to ips conversion but these
amount to only a pound or so difference



BTW  I've done the other math too, and come up with an approximate value of 410
joules/kilo brake weight delta per brake @ 100 kph,  for a total of 1640 for the
four.  This is out of a total value in the neighborhood of  500,000 joules.
Throw out an estimated weight difference of 2.5 kg per rotor and you have an
energy delta of 16,400.  This makes for a 3.3 percent energy difference, not
insignificant but not especially remarkable either.  This was done setting
vehicle weight at 1200 kilo, heavier the contribution is smaller, lighter
greater.  Disclaimer:  I'm an electrical engineer by training, not practice and
am familiar with mechanical engineering theory and can wade through an
engineering handbook, but I'm not sure the energy level is the total answer.  A
brake disc can be lighter AND be more effective, but I don't think it is always
more effective BECAUSE it is lighter.  Cause and effect, blah blah blah.  Using
lighter materials gives you opportunities to do different things. 

 I missed the start of this discussion, but gather it was something like: Team
Prowler guy says "Our newer better whiter-than-white and lighter brake discs
give us a shorter stopping distance."  Did anyone ask if they were larger?
enabled the use of a stickier pad? etc.

The real question is when they're going to make these discs into a cheap and
easy retrofit kit for my UFO brakes.

Joe Yakubik
BTDTM, ain't gonna read another post about Viper/Prowler brakes