69 Camaro Mini Tub - Leaf or 4 Link Coil over?

[srode]

In the planning stages of putting mini tubs in my 1969 Camaro, and have read comments about the spring rate needed on leaf springs for 2 or 3 inch lowered set up makes the ride quite harsh vs a coil over set up. In my mind, I'm struggling with understanding why the coils would be less harsh unless the available travel is longer before bottoming out - is that the case, more travel?

[79T/Aman]

Suspension travel at the rear with a stick axle is primarily dictated by the frame to axle clearance and when a car is lowered that distance is of course reduced regardless of the type of springs used, so unless the frame is altered to increase physical clearance neither the leafs nor the coil overs can have more suspension travel than the other.
The other point of contention is the shackle, if the bushings don't move freely you will get resistance as the leaf spring flattens under compression and grows in length, if the shackle bushings don't move freely enough the shock energy will transfer to the chassis instead of being dissipated, it also affects proper suspension travel and shock absorber effectiveness.
The angle of the shackles can affect ride quality, they should be straight down to angled rear ward.
Leaf spring design also affects ride quality, reversed eye leafs will tend to "pull" at the front bolt as the tire hits a bump instead of rotating the front eye bushing.
Remember that multi leafs are progressive, you can not compare one leaf spring to another, they all will have less rate at static ride height and progressively get stiffer in rate, this is another reason leafs can feel harsher they may have a ratting of 150# but as they compress you may have 200# rate, as where a coil spring that is most often constant rate of 150# will not get stiffer ( also don't compare the rate used by link systems vs leaf springs they have vastly different motion ratios )
Over load lowering type springs will have even less rate at static rid height and often will bottom out before the overload leaf make enough difference to avoid hitting the bump stops, ALSO too many people forget about the pinion snubber it may look like you have enough clearance to the axle bump stops but the pinion snubber is almost hitting.
The reason link suspension (coil over) feels less harsh is that the shock load from the road is spread over more mounting points, shock valving and bushing bind have far more effect on ride quality than anything.
For instance spherical bearings in the leaf springs will eliminate torsional bind along with free moving shackles the ride quality is very good.

[srode]

Thanks, makes good sense. I wasn't aware the coils didn't have progressive rates like leaf springs. Guessing that means they are also easier do bottom out unless there's non linear compression damping in the shocks?

[79T/Aman]

coils can be linear or progressive but multi leafs are always going to be progressive.