The only downside to Parabolic Leaf Spring is that it has lesser capability when it comes to carry heavy loads. 

As such, these types of springs are used for when comfort is more preferred such as the cases with passenger 

buses. Only the coil springs are offer more comfortable than parabolic springs. However, coil springs which are 

often attached only to a single point of the chassis have the disadvantage when it comes to load distribution.

There are also newer developments with parabolic springs with brings it close to coil springs when it comes to 

comfort.