I have a formula for weight to rolling resistance, it is
Rolling resistance (lbs) = vehicle weight (lbs) x 0.012 to 0.015
The constant is based on tire type, tire pressure, wheel bearings...
So, if you drop the weight of a car from 2000 lbs to 1000 lbs your rolling resistance (everything else being equal and using a constant of .013) would drop from, say, 26 lbs to 13 pounds. Compare that to a 2001 Jetta going at 60 mph and find that air resistance is 57 lbs and at 80 mph it goes up to 101 lbs.
The reduction in weight is small potatoes in comparison to air resistance with speed changes. Getting a "slippery" car is much more important since the air resistance is a function of frontal area and coefficient of drag. For the new models these numbers are:
Style``````````Cd````````````fA
Jetta``````````.3````````````20.6
NB`````````````.38```````````21.4
Golf```````````.31```````````20.7
The Cd numbers are coming straight from VW, but the fA numbers I am guessing at, if anyone knows the fA numbers I would be interested.
To get a fairly accurate number for the rolling resitance, you can use a bathroom scale. Place your car on a flat smooth surface in neutral, no parking brake (duh!). Then push on the bathroom scale on the bumper of the car. You should get an intitial high number that is the force needed to get the car moving and then a constant number that is the force of the rolling resistance...
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2001 Jetta GL TDI, 5 spd,
Black/Black,
Shift early, shift often!
[This message has been edited by jorpet (edited November 03, 2000).]