What, if any, are the advantages to a stiffer leaf spring? I was considering replacing the stock leaf springs in my'66 coupe,as they need it anyway, and was looking at the 165 lb/in rating.

 

well, from what ive noticed, better cornering but they cause the rear to bounce a bit, say if your going over railroad tracks. also better support in the back if you have passengers.

the more leafs you get the higher/stiffer it will be, but more leafs is really for passengers or hauling (if you have a truck and have alot of cargo)

They make springs that stiffin but also lower, those would be reverse eye and mid eye

 

depending what you do to the rest of the car and what you want to use it for, increasing the rear spring rate will make the ride firmer.

it will improve handling to an extent but that depends on also replacing bushings and making sure there is a balance between front and rear. for example, if you are hard rear springs and soft front springs then your car will likely be tail happy.

you also need better shocks if you go higher spring rates as the shock is controlling the spring.

 

I went with 4 1/2 reverse eyes on the rear of my 68 ( not the springs in my avatar or below my post ).
It is, I would say they are a bit too stiff. Also even though the reverse eye was supposed to cause it to sit lower,
it doesn't as the springs give little with the weight of the car. Also up front I have 620lb springs, but with the
aluminum heads, manifold, headers etc, even with the 1" shelby dropthe car sits the same height as the
original springs. I'm not too fussed about it though, as in Japan all roads are near race track quality, so
stiff suspension is not really an issue.

Jav