What's the difference in "Progressive" vs "Specific" rate lowering springs?
 

don't laugh!

Progressive rate springs have bigger gaps between the coils at the top and bottom and smaller gaps in the middle. What this does is allow the spring to compress alot in a slight lean or over bumps, but the more force that gets applied to the spring such as a hard corner, the stiffer the spring gets because you start to compress the tighter coils. These are good for someone who is anal about keeping good ride quality, but wants "a little" more performance. This setup allows quicker turn-in than stock, but is still not really considered "quick" turn-in. Turn-in is the immediate controlled RESPONSE during a corner, like if you are going straight and suddenly pull the wheel on an autocross car it will "turn-in" very fast while being accurate and the same speed left turn in a '53 buick the right side of your bumper would scrape the ground, VIRTUALLY having no turn-in.

Specific rate springs have coils which are evenly spaced these provide very fast turn-in, but don't "absorb" as much of the road and unfortunately are a little harsh over even small cracks.

got it? good. Now go get some 650 lb specific rate springs!:D

kidding, that's just what I bought altough I haven't yet installed them.

cool, Thanks.

lx5091 did a pretty good job of describing how they are different
this is just a couple points to add in
specific rate springs have one spring rate thoughout the entire spring and a linear response (i.e 650lb/in) so in this case it would take 650 lbs to compress the spring one inch and another 650 lbs to compress it another inch.
Progressive rate springs do not have a linear spring rate. I don't know exactly what the rates are but it may only take 300 lbs to compress the spring the first inch and then as you compress it more you would work up to say 650 lbs per inch.

Progressive springs are better for someone that wants to increase looks and handling a little while maintaining smooth ride qualities.

Specific rate springs are better for someone looking for more performance and better lowering qualities and willing to sacrifice the smooth ride quality a little bit.

The BBK springs I have are specific rate 650 lb/in and I like them. They are not too harsh and I think specific rates are also cheaper.

the specifics are cheaper, and do all the BBK specifics have 650lb rate?

wondering cause i have them on my car and always wondered what the rate was.

I think they only make one specific rate set for mustangs and they are 650

Re: What's the difference in "Progressive" vs "Specific" rate lowering springs?
 

Ok got a quick 2 quick questions. I have Eibach sport line spings on my 2000 mustang GT coupe, and with 2 jl audio w7 in the back which makes the back lower than the front and I basically want it up a little more. The other thing is that I am trying to do my suspension this year so that next year i can do a new engine w/ kenny bell w/ a 2.6 or 2.8 sc. thx.