Re: Unsprung weight - was: two transfercases

[Curt Cleavinger <rcleavin@domain.elided>]

>Not just ride quality, but articulation, undulation and everything in
>between. The body tends to move less and the suspension more in relation to
>the ratio of sprung weight/unsprung weight. Simple physics - inertia.
You're talking about driving on a washboard road at 40 mph, I'm talking
about crawling over rocks at 2 mph - inertia drops out of the equation
for my example. I think more unsprung weight would probably improve 
articulation for the low speed case, since (for a given spring) the 
heavier axle/wheel will tend to droop more.

>And I think that we're talking about more than "ride quality" here. It's
>the whole action of the suspension: axle assembly in relation to body
>thing. Otherwise, we wouldn't even need springs, just solid mounts would
>do. And, if sprung weight could equal unsprung, that is probably how it
>would work - just like it had a "solid" suspension.
Agreed. If you had a trail-only rig, you might very well come up with
a design that didn't include springs. The vehicle that they built and
sent to Mars to crawl around - did it have springs? anyone know? Do 
road graders, earth movers, front end loaders and other heavy 
equipment have springs?

> But a vehicle with more unsprung weight will have a lower
>center of gravity, and less of a tendancy to lean or roll over in 
>off-camber situations - a Suzuki Samurai with front and rear dana 60's 
>would be very difficult to roll. And at very low speeds the ride
>quality isn't an issue.
>
>I'll give you that. But do you think a Suzuki Samurai could even turn the
>dana 60's? Ride quality not an issue - perhaps. But how you going to drive
>this thing on the freeway? A little "whoop-de-do" and you'll be airborne
>going 60 MPH! 
Maybe you're not going to drive it on the freeway. Or maybe you're 
willing to live with a 50 mph top speed for a truck that was built for
the trail. I'll grant you that increasing unsprung weight will tend to 
have a negative impact on a vehicles *highway* driving characteristics. 
But sometimes that's not a concern, or it's a secondary concern. 

>I don't know, I have this strange vision of a Samurai bouncing along a
>rough road with axles/wheels/tires that are bigger than it is. Like one of
>those "exagerated" cartoon charactures of a 4WD vehicle they put on
>T-shirts.
I was giving a (somewhat) extreme example to illustrate the point. But 
that just demonstrates that in between the extremes is a multitude of 
choices. For each choice, you need to evaluate the desirable and 
undesirable effects of each choice with your intended application
in mind. If I wanted to build a great highway cruiser I'd make one choice,
for a baja racer I'd make another, and for a rock crawler I'd make another.
You sounded like you were making a blanket statement that unsprung weight
is bad and should be minimized, and I was making the point that it depends
on your intended application - for some applications increased unsprung 
weight can be good. It depends on what you're trying to achieve, and 
whether you're willing to tolerate whatever undesirable side effects there 
may be. 

Later,
  Curt
   rcleavin@domain.elided  San Diego, CA
   Binder Bunch: http://www.off-road.com/~jweed/binder.htm
   Scouts West: http://www.scoutswest.com
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