Un-Sprung Weight.

[ianfox]

Does anyone have any thoughts on the advantages of increasing/decreasing unsprung weight? I am about to start the build of my 2001 Academy Car with adjustable suspension and I have seen pictures of other sevens, some with the dampers (springs down - less unsprung) some with dampers (springs up - more unsprung). What is the best way of fitting these?

 

Regards.

 

Ian.

[Matt Prior]

By my reckoning, turning a spring/damper unit upside down increases, not decreases, the unsprung mass.

 

Why? Because the damper end is heaviest - so should be bolted to the chassis (where it's sprung), not the wheel (where it isn't).

 

The right way up then (damping unit at the top) seems to me to be the best bet.

[Paul Ranson]

> By my reckoning, turning a spring/damper unit upside down increases,

> not decreases, the unsprung mass.

 

Does the piston and rod weigh more than the casing and fluid?

 

I think it's insignificant. Upside down is good because you can change springs without removing the damper, and because it keeps the adjusters further away from road dirt.

 

And anything that unsettles the opposition is worth doing.

 

Paul

 

[Chelspeed]

Come on guys, you're both saying the same thing.

 

It's better to put the damper body on the top (chassis end) and the piston rod on the bottom (wheel end).

 

Whether this is upside down or the right way up depends on what you are used to.

 

Some kinds of damper only work when the piston is at the bottom, so damper down is "the right way up". This is why Paul calls damper up the wrong way up.

 

Some kinds of damper work either way up (Caterham's Bilstein is one of these) in which case it's theoretically better to reduce unsprung weight so damper up is "the right way up". This is why Matt says damper up is the right way up.

[Matt Prior]

That's what I thunked.

[Graham Perry]

I have read various books on suspension set up over the years. Most of them say the same thing. Aim to get unsprung weight to about 35 to 40lb per wheel. Apparently if you go significantly under this amount, the tiny improvements gained are not worth the trouble.