There are a lot of features in the LHB coaches that were not used in IR earlier -
1) Bogies - The Bogie (the part of the coach containing the wheels) plays the most important part in deciding the speed potential and ride quality of the coach.
LHB coaches have a different bogie compared to the ICF bogie, called a 'Fiat' bogie. This design has several advantages over the normal ICF bogie, particularly at high speeds. In addition, it also has features that improve the ride quality.
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Bogie-Shell connection -
The main body of the coach in which passengers sit, is called the 'shell'. This is mounted on the bogies through various mechanisms.
LHB coaches have a different arrangement compared to the conventional ICF coaches in connecting the shell to the bogie. The system in LHB coaches improves ride quality and simplifies maintenance.
3) Electrical systems and brakes - LHB coaches have a modular electrical system and electrically controlled anti-skid brakes, using disc brakes mounted on the wheels. ICF coaches have a much simpler braking system. (For those familiar with the brakes used in motor bikes, this is like the difference between Drum brakes and Disc brakes).
Of these, 1 and 2 are the most crucial differences between ICF and LHB coaches and had to be obtained from Alstom (who took over the LHB company in 1998), who had much more experience working with such designs than IR.
No.3, even though very important, was something that ICF could have eventually developed in-house within a short time.