Difference with m-technik suspension?
 

I see that some sights claim that a certain suspension will work on a 318ti that is not an m-technik. What is so different, and how do I know if I have the m-technik suspension?

Do you have a sport edition car?

If you're replacing both the springs and shocks it doesn't matter. Those parts and the swaybars are the only functional differences between the M-Technik/Sport cars and the standard cars.

I do have a sport edition

If you have a sport, then you should have the M-Technik suspension. That just means your car has slightly shorter/stiffer springs, thicker swaybars, and different shocks than the Active or Base model cars. That's important information if you're buying any of those parts from a dealership as they'll need to know which to supply you with. If you're buying aftermarket stuff it doesn't really matter, especially if you're replacing both springs and shocks. The only reason I've found that some suppliers specify is that the amount of drop you get by putting on lowering springs is less if your car already had the sport suspension, i.e. if you put the Eibach Pro-kit on your car and they say it will lower it 1.2 inches you won't get that full measurement if you were already sitting on lower springs. Here are the numbers I came up with when I was researching springs:

With a 16 inch wheel:
Front
Standard suspension - 589mm (23.19 in)
Sport suspension - 574mm (22.59in)

Rear
Standard - 531mm (20.91in)
Sport - 520mm (19.96in)

So, Eibach claims a 30mm drop with the Pro-Kit. I'm pretty sure that means 30mm off the standard height, not the sport height. Incidentally, there is a misprint in the Bentley manual for the front heights. They hosed the mm to inch conversion for the sport suspension.