# Suspension diagram

```On Mon, 19 Feb 1996, Eliot Lim wrote:

> i have never figured out the math & physics for unsprung weight, just
> that a teeny weeny bit of reduction goes a long way.
>
> which mass, spring & damper model applies to unsprung weight?  anyone?

Here's a shot at ASCII Dynamics;

|				|
|	Car chassis Mass	|
---------------------------------
\		|
/		|
Susp.	\	    | ----- |Suspension damper (shock absorber or strut)
Spring	/	    |_______|
\		|
/		|
-----------------
|Suspension	|  Includes; Hub, rotor, caliper and mount bracket,
|Mass		|	     lower portion of shock, part of spring
|		|	     part of antisway bar
-----------------
Tire	\		|
spring	/	      |_|_|
inc	\	      |___|Damping within tire
air	/		|
press___\_______________|_________  Ground

For representative values, the following are common

Susp spring - 100 - 300 pounds/inch
Tire spring - 30-70 pounds/inch
Air pressure - aprox 50 pounds/inch per psi of pressure

Damper values are described with a graph of force vs velocity.  In other
words, they exert a force on the attachment points, opposite to the
direction of motion, and directly(somewhat) proportional to the speed of the
deflection.

They look sorta like this;

F	|                       *
o	|                *
r	|           *
c	|        *
e	|      *
(pounds)|   *
|*___________________________

Velocity (in/sec)

In addition to the masses of each item, there would be inertias for each
item, which would resist motion similar to a damper.

> >but it was a \$28.00/rotor
> > hit, above the price of iron rotors!!  That's alot in OEM terms.
>
> well, that's not bad if you consider how much people are paying for
> alloy wheels over steel...

Yeah, but that's likely more than they pay for an iron rotor in the first
place, so to increase the price of the rotor by over 100% is not
acceptable at an OEM level.

HTH

Later,
Graydon D. Stuckey
graydon@apollo.gmi.edu
Flint, Michigan   USA
'86 Audi 5000 CS Turbo Quattro, GDS Racing Stage II
'85 Mazda RX7 GS 12A-leaning-towards-a-13B-soon

```