Springs and shocks are designed to work together. Springs have certain spring rates (measured in how many pounds of load are needed to compress a spring one inch). Shocks have compression and rebound rates designed to handle specific spring rates (shock rates are therefore a little more complicated). The stock shock is designed to handle a narrow margin of spring rate...read the maufacturer designs the original equipment shock to handle the intended stock spring rate (not much more or less). The length of the shock also corresponds to the stock spring and amount of travel designed for the car.
Since the spring you want to use is considerably stiffer and shorter it is a mismatch for the stock shock. You need a shock that will handle the increased spring rate and has a shorter body to maintain some suspension travel (primary compression) without bottoming out all the time.
Can you use the stock shock...yes...but for the reasons stated above it will not adequately dampen the new spring, it will bottom out and will eventually destroy the valving sooner than later, and you will find the meaning and purpose of bump stops far too frequently. Do it right the first time and enjoy what a well designed suspension can do both in terms of handling and improving looks if thats one of your main purposes. Function should be given priority over looks.
sorry to go off topic, but MAN is this guy smart!!! Every time I do a search on something related to the wheels/tire/brakes/suspension forum, 9 times out of 10 I read something he wrote, and it totally answers my intended question (one reasons I have so few posts on here). Don't ever leave, Geezer...
You're making me blush. Yes, I have learned from experience. More importantly I like reading various opinions on things. This way you can draw your own "informed" conclusions. Just remember, cars have been around for a long time. Braking and suspension issues just as long. There really isn't much new happening. The formulas and calculations the engineers use remain the same. What's changed is that computer design allows those same engineers to test a product before its even manufactured. In the old days you had to build it, try it, tweak it, and then do it all over again for each permutation. It took a long time for things to get to the market.
The single most important thing I can recommend is to take any marketing hype with a grain of salt. Its marketing...they're trying to sell something....let the product speak for itself. Well known companies like Eibach, Koni, Bilstein, Brembo, etc. have been around along time for good reason....they make quality products that work. Yes, you may pay a little more but in the long run these kinds of products pay for themselves.
My second word of advise, believe only half of what you read in these forums, including my ramblings. Do your own research, you'll learn so much more than listening to heresay. There are lemmings following lemmings and blind leading the blind here. This occurs in most forums its nothing new as well. My sole intent in most discussions is to politely challenge those who make misleading and sometimes flat out false statements. Hopefully they will learn or at least question those that they got their info from. Many people are here because they truly don't know much about cars and thats great! They deserve honest, straight forward answers and help finding the info they need. I came here because I wanted to learn about the nuances of the Focus. I have honestly learned a lot. I can honestly say that dollar for dollar it is the best car (of over 20) I have owned. With a few bolt ons this is one nice handling car. I enjoy driving it as much as my Miata (which is the most amazing handling car i have ever driven period).
And kudos to those of you who have tried things that don't work and ADMIT it. That old adage that you learn from yours and others mistakes is soooo true. Its better to admit a mistake than try to defend or make excuses (or worse, blame someone or something else) for why something isn't working.
I also read countless periodicals. The two I find actually helpful are Grassroots Motorsports and Sport and Compact Car. Grassroots Motorsports is more for those who are preparing a vehicle to race, rally or autocross. I like Sport and Compact car because the majority of writers are young mechanical engineers who like to try products that are being hyped and are not afraid to bash them or praise them after reasonable research and testing. Its always nice to let someone else spend the money before you do isn't it?
So much for the ramblings of an ol fart (if you need to know I'm 57 and trying to teach the same things to my 21 and 25 year old sons).
PS I have no desire to be a moderator, the guys here do a fine job!