Getting the instant center takes more than a tape measure ... you need will some drafting skills.

Something else not dwelled on above is what happens to your roll center (and the instant center) as well when you lower the front. 'Typical' with a McPhearson strut type of geometry is roll center gets lower, which means the front end roll couple gets bigger and 'generally' you need more roll stiffness to counter act it ... if not other adverse things can start to happen like the o/a roll stiffness starts to shift to the rear ... this spells over steer. Roll stiffness is provided by the suspension, sway bars and transitionally by the shocks.

Yes there is a lot to understand.

Steeda has two ways to solve the change in front roll center. One is to raise the inner pivots of the upper a-arm, The other and not yet available is to lower the lower ball joint.

Also checked my 05 tonight. For the rear springs, there are very roughly about 8 active coils (give or take a little as very hard to make a accurate assessment with then installed). Assuming 8, and everyone seems to have settled on two cut coils for the rear(?) then you can expect a (8/6 -1) x 100 = 33% increase in spring (or wheel) rate. Something to take note of is the spring stiffness distribution (including roll stiffness) is now moving towards the rear axle. Generally speaking, at some point that equates to oversteer type stability. ideally, even for a family or race track car ... you want netural or slight understeer.

 

I'd be concerned about the spring lengths. I thought I read in the Eibach install article mentioned above that the smaller section of the spring in the rear didn't provide any support but was simply to "keep them in place" under full suspension travel. Personally, I'd be worried that the rears could fall out under the right circumstances. The front's are at least constrained by the strut but they're obviously loose after the mod as well since no compression tool is needed.

 

There is absolutely no way the rear springs could fall out. With the car raised, and the rear-axle lowered all the way, the rear springs (with 2 coils removed) are not easily removed.

I'll be installing my Bassani X-Pipe in the next few days. When I do, I'll take a couple pictures to show this is impossible, especially when it is sitting at ride height.

 

Update...

After two weeks of driving my lowered stang (I cut the springs per the writeup provided by Dave) and everything is feeling and looking great. I went out a few days ago and took her through some very spirited cornering (Austin stangers: Lime Creek Rd.) and I love the improved handling and feel!

So I took her to the Ford dealer today to check out a rear-end scraping noise and had them check the alignment. Only a slight tow adjustment was needed. No camber kit was needed and no camber/caster adjustment was necessary. It seems in my case cutting the springs and lowering 1" - 1.5" didn't affect the alignment much at all.

However, I do plan to get her checked out regularly to keep an eye on things.

 

This is a great topic. back in the late 70s I was cutting coils and removing rear leafs because thats the only way we had to drop a car. All my buddies were jacking thier cars with airshocks, I was dropping mine. I had a 63 Falcon with a 200/6and a 3 speed that would smoke some pretty big guns on a curvy road.

I had Ford Motorsport lowering springs on my 88 GT. The ride was so harsh I took them off and bought new oem coils and cut them. Loved them.

I put oem SVT springs on my Focus, dropped it about an inch, loved them.

I dont want to go to the trouble that messing with the front suspension brings, so Im cutting 1 coil off my rears to bring the rear height close to the front height. I dont carry passengers or cargo in my Stang so Im ok with it. Im also going with larger tires next time around so I dont want to go to low.

I had a flat the other day and couldnt get my floor jack under the front end, ggod thing that sissor jack works well.

Anyway, for a mild drop cutting coils is fine. I have thousands of miles, maybe even 100,000 miles on cars with cut coils with zero problems. The only thing I did was watch the tire wear, you can chew up a $100 tire in no time.