# [Vwdiesel] mileage

Val Christian val at mongo.mongobird.com
Sun Nov 29 13:37:50 PST 2009

```Well, kinetic friction would be a tire sliding on the pavement,
and static friction would be no relative movement.  Ideal braking will
have neither individually or a combination of both.

Mass of a vehicle will impact at least two factors (actaully more):
-the total kinetic energy to bleed away
-the normal force in friction

Other factors include the moment of the mass, and how the weight shifts
between tires, etc.

>
> I don't disagree with anything about there being differences in the
> brakes, and that causing differences in braking. I'm more interested
> in differences in stopping distances between a passenger car and a
> semi truck with brakes locked up. No slipping of the brakes, pure
> kinetic friction between the road and rubber. Ever since I first heard
> that mass didn't come into the equation it's interested me.
>
> But I also suspect, after further reflection, that truck brakes are
> somewhat limited from locking up, at least on the cab, from a
> standpoint of retaining control. If you have too much more braking in
> front you're in danger of jack-knifing and losing all control. I am of
> the opinion that it is likely more dangerous to have complete loss of
> control and jack-knifing, with the trailer going all over the place,
> than having a longer stopping distance while limiting the amount of
> braking going to tires at the front of the 'train.' This would also be
> consistent with an unloaded trailer having a longer stopping distance
> than a loaded trailer. I bet it's not a simple thing, but is very
> closely controlled to optimize braking while retaining control.
>
> I know that ABS can have a drastic difference on stopping, because of
> its superior properties, but in this I'm thinking that neither vehicle
> would have ABS to simplify and make the two more similar.
>
> Erik
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```