Why should I replace the stock springs on my 20 year old RX7? I can see how some people want to lower their cars for better looks and handling. But my springs are already sagging; I bet I already dropped an inch. I'm not looking to go any lower.

I don't want to invest in coilovers; they are too expensive for me and I don't want to go any lower; I'll bottom out on every driveway. This car is my daily driver (when it isn't snowing) and I don't want a teeth chattering ride. I don't do AutoX or Track days either.

And some people want progressive springs like Eibach rather than linear springs; but then again some prefer linear springs. I'm leaning towards linear, too. Which is what I have now.

If I like my ride height as it is, and the linear effect of the springs. Why replace what ain't broke?

I know I could benefit from a new set of shocks, but I would rather save the money for replacing springs and put it towards adjustable shocks. That way I can make it softer for in town but make it firmer for sporter driving events. Also, I think adjustable shocks could add more resale value than non-adjustable shocks with shiny new springs.

So why, why should I get new springs?

 

For your particular situation, it does seem like you'd be better off just replacing the shocks and any worn bushings.

People replace springs for 2 reasons:
1. b/c a lowered car looks cool
2. b/c they are racing, autocrossing or doing track days

 

If you aren't having any bottoming problems you probably don't need to buy new springs.

Manufacturers go stiffer when they make lowering springs because they have less travel to absorb a big bump.

 

Cruisin' down the road, you'll be just fine on saggy old stock shocks.
But...
- when you brake, new stiffer springs will keep your nose up higher
- when you accelerate, new stiffer springs will keep your back end from squatting
- when you change lanes on the highway, stiffer new springs will keep you from wobbling (add anti-sway bars too)

If you had to do an emergency maneuver , new springs could help you stay in control.
But of course , good shocks/struts play a big role here, too.

 

You said, why fix what isn't broke. A sagging spring means a broken spring, just not in the literal sense. As John said, your losing performance. And there's no point driving a sports car if your not going to keep it up to par. If you like the stock car, just replace the springs with stock ones. Maybe some new shocks. If the car is that old, you'll need them. I upgraded everything on my 84 and it's not overly harsh unless the road gets retarded ie: the construction on wellington at the 401. Even replacing everything with stock you will notice a significant increase in your cars abilities. If you like how your car looks if the springs are sagging and its lower than stock, to keep it there you will need lowering springs. Stock springs will end up raising the car back up higher than it sits now.

You don't have to use a coilover system, you can just piece your suspension together. The difference is that in a coilover system, the parts are designed to work together, whereas piecing it all together, you get different parts from different companies, and they are just designed to improve on the stock piece alone. Replacing your shocks and leaving the old saggy springs will just destroy your ride. It will be overdamped and rough, and your more likely to ruin the new shocks as the springs get worse. The springs are there for a reason, and although its a simple part, people tend to overlook their importance. If the springs are bad now, they'll only get worse, if your putting new shocks in, you might as well do the springs. The resale value may go up with adjustable shocks (however not by much) but thats until the buyer bargains the price down because he now has to go and replace the worn out springs. If your in it just to sell the car, sell it now as it is, and let the new buyer worry about it. You have to drive it now, so might as well keep it in good shape.

Good Luck

 

faster weight transition
more resistance to roll
lower center of gravity (if you get springs that lower)
better handling in general

what you are thinking of doing (performance shocks set on stiff with stock springs) is technically an overdamped condition, where the compression is too stiff such that the shock is absorbing part of the bump instead of damping spring oscillation only. i guess that works, but i'm not sure its kosher from an engineering standpoint.

i do remember from linear algebra that in oscillatory systems, damping is ideally set at the critical damping value, where the system will return to the rest state in the minimum amount of time. the problem with overdamping is that it should technically extend the amount of time needed for your suspension to come back to rest state.

ooh look what i found

 

I tryed to explain this to my friend the other day, so i drew this up to show him. Do you think its accurate?