Could someone please explain to a simple chef what the (obvious?) difference between the two is, which is good and which is bad-and why?
Cheers, Mart.
Basically everything that can move up and down when you compress the springs (by pressing down on the car) is sprung weight, everthing that can't is
unsprung weight.
Wheels, tyres, brake discs, calipers for example, are all unsprung weight.
The idea is that the less unsprung weight
you have the easier it is for your springs and shocks to keep the tyre in contact with the road because of the reduced inertia.
So the easier it is for your shocks and springs to do their job the better.
Probably someone will explain it better, but I hope that helps.
Unsprung weight is all the weight on the car that is not carried by the springs - believe it or not! This would normally include wheels, tyres, brake
disks and calipers and a percentage of the weight of drive shafts, suspension arms etc.
Sprung weight is the weight on the car that is carried by the springs and includes - well, everything else really!
In the simplest of terms the unsprung weight is important as it dictates the speed or ease at which the suspension reacts to changes in the road
surface.
The higher the unsprung weight relative to the sprung weight and the more likely any deflection of the road wheels will be transfered to the body of
the vehicle rather than absorbed by the susspension.
Think in terms of inertia - the wheels etc are a mass and the lighter they are the easier it will be to deflect them. The rest of the car is another
mass and the heavier it is (Compared with the unsprung weight) the less likley it is to be deflected and the more likley it is that the movement of
the road wheels will be taken up by the springs.
In reality it is far more complicated than that but there is the basic idea.
Reduction in unsprung weight can be carried out in many ways - the most obvious being changing whels for lighter ones - hence alloys. However alloys
have now become fashion items as much as tuning accessories and it no-longer necessarily follows that your new set of shiney alloys are any lighter
than a good set of steel wheels.
Other ways of reducing unsprung weight include IRS as opposed to a live axle so that the weight of the diff is carried by the chassis of the vehicle
rather than attatched to the unsprung axle. Inboard disks and callipers are another way of reducing unsprung weight.
I've just read my previous post and it sounds a little garbled - too late and too much beer. I'm sure someone will clarify it for you if it makes too little sense.
An example:
Consider IRS v live axle.
If you imagine pressing down on each of these you can easily see what moves relative to the road, and what doesn't 
On the live axle you have wheels, tyres, hubs, brakes and the whole axle and diff as unsprung weight, all has to be controlled by the
springs/shocks.
Compare to the IRS where only the wheels, tyres,brakes and hubs are unsprung, but significantly the diff. is not.
Obviously in the case the springs/shocks have an easier job keep the tyres on the tarmac 
Cheers Guys,
Funny how it all seems so obvious once somebody explains it. Appreciate the help. Oh, and by the way, both explanations make sense, even after a
beer!!
quote:
- too late and too much beer......
