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From: lee@unmvax.UUCP
Newsgroups: net.auto
Subject: Re: Suspension systems
Message-ID: <311@unmvax.UUCP>
Date: Fri, 27-Apr-84 01:57:47 EST
Article-I.D.: unmvax.311
Posted: Fri Apr 27 01:57:47 1984
Date-Received: Sat, 28-Apr-84 10:20:10 EST
References: <7368@decwrl.UUCP>
Organization: Univ. of New Mexico, Albuquerque
Lines: 57


 Wow. What a question! Here's a couple of reasons:

Unsprung weight
travel
progressive damping (dampening?)
sway control

Anyway, these four things are pretty important when speaking of suspension
systems. Briefly:

Unsprung weight is the weight of the parts that are below the shocks.
Things like, the wheels themselves, brake parts, calipers, etc..
The heavier these are the less responsive the component is. The
faster you go the harder your shocks need to work to dampen the
motion and get the wheel back under control. It is pretty desirable
to have the wheel in good contact with the pavement at all times.

Travel. This is a measure of how far the wheel can pivot before it
strikes some part causing it to stop dead (read HARD jolt friends).
The more of this, the more time those shocks have to get things back under
control. Oh yeah, this is usually movement upwards by the wheels. Cars
don't fly, usually.

Progressive damping. Neat thing to have. When your toodling along
the highway the shock doesn't try to stop the wheel very much at the
start of compression. Makes for a nice ride. The harder you push
the car the further the wheels will travel. the shock gets stiffer
and hence the ride stiffer. Air shocks are great for this. They are
"infinitely" progressive. Air is not easily compressible. Thus, the more
you try to compress it, the harder is resists.

Going around a corner where the body wants to lift on one side is a BIG
problem. The shocks don't like to expand either, so they control this, though
usually well out of proportion to their resistance to compression. Sway bars
help in that they effectively tie (to a degree) the two sides of
the auto together forcing it to try to push the inside into the pavement,
improving traction.

Big cars have alot of mass. 2,000 punds being loaded down on the
suspension takes a LONG time to stop. These cars are usually meant
for fairly slow speed (< 90 MPH) and use softer shocks so that the
wheels take more of the jolt. Push 'em too far and the wheels
can't be kept in contact with the pavement as they flail around.
Go around a corner, hit a bump and LURCH to the outside.

Sports type cars, meant to drive at higher speeds, need stronger shocks,
in proportion to their mass so that when they get going REAL fast
the wheels come under control very quickly should they hit a bump.
Too bad, at low speeds this means a harsh ride as they stop wheel motion
very quickly transferring more of the jolt to the body than the
large beasties.

The automakers try to trade off on ride and handling but they ARE
mass produced.
-- 
			--Lee (Ward)
			{ucbvax,convex,gatech,pur-ee}!unmvax!lee