[Spits] Softer than stock front springs

[Jim Muller]

On 28 Dec 2007 at 10:47, M D Nugent wrote:

> - a 2" reduction of free length will result in a 2" drop in ground
> clearance, and...

For any given weight, the loading within the spring is the same 
everywhere.  Regardless of the free length (and assuming a linear 
spring), if the spring compresses an amount X and original length Y, 
that compression will be linear within the spring.  If it compresses 
a fractional component Z = X/Y, then the new length will be shorter 
by Z times 2in, not shorter by 2in.

To put it an other way, you must distinguish between the compression 
modulus of the coil as a material and the effective compression 
constant of the actual spring as a unit.  The effective spring 
constant is the compression modulus (dimensionless w.r.t. length) 
times the spring length.  If you shorten the spring its effective 
rate goes up so a given load compresses it less that you'd expect.

> - reduction of front weight by 40% would require a spring with 40%
> lower rate for "same as stock" performance.

Wow!  How does one reduce the front weight by 40%?  Install a 2-
cylinder engine??  Cut the Spitfire engine in half, factor in the 
lightened frame, suspension, and brakes, move the battery to the 
trunk, remove the alternator, lights, horn...

-- 
Jim Muller
jimmuller at rcn.com
'80 Spitfire, '70 GT6+