Re: [alfa] Unsprung weight

["The Baylys" <dabaylys@xxxxxxxxxxxxxx>]

Biba,
it's anything NOT supported by the springs.

So, if you add weight to the item and the car doesn't 'sink' on the springs,
then you've added unsprung weight.  Of course, for small increments one
needs to imagine the above scenario as there may be no perceptible movement.

If you have a high (or is it low ?) sprung-to-unsprung weight ratio then the
vehicle will be easier to make ride comfortably (think XJ-6 Jag, RR etc).
This is because any forces acting to push the wheels upwards, are less
likely to affect the larger mass of the rest of the vehicle; the sprung
weight (mass).  If you compare this to say a Lotus Seven, then the ratio is
quite the opposite and the car is more likely to be affected by every
vertical movement of the wheels (buckboard ?).

It's not merely the ratio though as any moving unsprung parts (wishbones,
WHEELS, TYRES) have there own inertia which needs to be overcome to send the
suspension skyward.

The experts say that any suspension component which is not supported by the
spring but are hinged to the chassis (eg wishbones, leaf springs, driveshaft
on a 105 but not on a 116) contribute half of thier weight to both sprung
and unsprung calculations.

And, a torsion bar is all sprung weight.

Beatle
Oz



----- Original Message ----- 
From: "alfacybersite" <acs@domain.elided>
To: "AD" <alfa-digest@domain.elided>
Sent: Saturday, August 28, 2004 4:56 AM
Subject: [alfa] Unsprung weight


> I've been using the term for ages, but have no idea what it really
> means. I always assumed it simply meant a combination of all the items
> on the suspension, wheel / tire, brakes, etc. But if that was the case,
> it would simply be called suspension weight or something such as that.
>
> What got me thinking about this was a 64 pound package which just
> arrived via the man in brown from IAP. Four red springs and four red
> shock absorbers. Even dividing by four, I'm thinking that is a lot of
> "unsprung" weight. Thinking further it occurs to me the spring is
> pushing upward. Does that add or subtract to the equation? Then there
> are the shock absorbers...
>
> Don't get too technical, I'm not a racer guy and this is merely a
> curiosity + I'm sort of laying low since the Sheriff's helicopter flew
> over while I was primering late last evening. Then later a small plane
> flew directly over my, unh, err, exterior spray booth, at a pretty low
> altitude. Big Brother or merely paranoia? Only time will tell.
>
> Biba
> Irwindale, CA USA
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