That's the trouble when you start to change things which have been engineered to a specific design.
If you want a giggle have a search for suspension lift in the messages of this forum.. its been discussed many times.
The reason they don't tell you is that (in my view) they want us all to believe that we can just bolt stuff on to our vehicles without any thought and instantly make them "better", or more "extreme". If they actually tried to provide some useful information with the equipment they punt, including the good and bad points... they may not sell as much.
A jaded view maybe... but sadly I fear it may be true.