Spring rate for rear coilovers

[ColoradoSteve]

I found these http://www.ground-control-store.com/products/description.php/II=749/CA=159
to install on '87 951, would not be removing torsion bars. What would be a good spring rate for city/highway driving, good cornering capability, was thinking 300?

[flash968]

if you have the 23.5mm torsion (126#) then i would say about 150# for the helper spring - the math makes that about 210 wheel rate

if you have the 25.5mm torsion (175#) then about 90# for the helper spring - the math makes that about 225 wheel rate

we set up a 968 with coilovers on 25.5mm torsions and used 90# springs - VERY nice

then you can change the front springs to about 250#

remember that the torsion bars establish the ride height - you will need a small amount of preload on the spring just to keep it quiet - that means that the rear will come up a bit with a helper setup like that - you can install a tender and coupler though to eliminate that preload - that's what we did on the 968