RE: Unsprung weight & Coil overs

["Bergman, Micke" <M.Bergman@domain.elided>]

Unsprung weight is important, especially on a rough road. On a smooth track
the difference isn't that big.

Anyway. Assume you run a rough course and care a lot for this.

The assumption of the unsprung weight of 40 lb is somewhat optimistic.

Tire: 20 lbs
Rim: 16 
Brake disk: 9 (solid 2.0)
Brake caliper: 5 
Hub: 6
Upright: 9
Lower A arm: 22 (of which ~30% is unsprung)
Upper control arms: ~14 (of which ~40 is unsprung)

My 600 lbs front coil spring weighs 4 lb of which 30% is unsprung -
significant - I make my conclusion - you make yours.

BTW. You're right about push rods and beefy A arms. Using coil overs enables
to use A arms of 7 lbs.

PS! Any idea what 27 mm torsion bars weigh? And the solid iron transverse
the rear end attaches to? In addition to the A arms it makes interesting
calculations for front end weight.


Micke
GTV 2.0
183 hp / 1990 lbs
Coil overs & decent handling


-----Original Message-----
Subject: Unsprung weight and wheels

Adding 4 lbs per wheel of unsprung weight is a significant deterioration. 
The wheel/tire package probably weighs less than 40 lbs so that is 10%. 
(try adding 10% to the sprung weight and note the performance penalty). No 
sense spending money on light alloy wheels and light strong performance 
tires only to add unsprung weight you don't need (to be fair not all the 
coil over will be unsprung, usually about half)

Torsion bars require beefier suspension components than stripped down coil 
over suspension. But for a heavy road car the A arms need to be beefy 
anyway. For racing cars note the coil overs have been mounted in fully 
sprung weight position for many years with only the actuating rocker arms 
unsprung.

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