Why is it bad to lug an engine?

[leonardc9]

I've always been told it's bad to lug an engine. On the other hand, I've been told with my car that it is most efficient at low RPMs with max torque (for example, 6th gear going uphill vs. 4th gear). My car can do this smoothly but my monster engine isn't happy below 3K RPM. Other than potential stalling though, why is lugging an engine considered bad? Or is it an issue specific to Monster engines?

Thanks,

Leonard

[ROBsS4R]

People always told me it puts more strain on the engine components. I have no idea if that is true or not. 

I can't really ride my S4R lugging it so I guess I don't need to worry about that 

[He Man]

i heard your engine is working harder to move the pistons and it ends up dragging on the walls of. 14T or +2 rear = no more lugging at low gear!

[swerdna]

Lugging causes extreme stress between the rear thrust faces of each piston and the cylinder walls. Small bits of piston skirt can break away causing the rear surface to scuff. The best prevention for lugging an engine (either old or new) is to downshift to a lower gear where the engine runs more freely, and the transmission assists the engine in delivering peak power to the rear wheel.

Source

[hypurone]

Lugging causes extreme stress between the rear thrust faces of each piston and the cylinder walls. Small bits of piston skirt can break away causing the rear surface to scuff. The best prevention for lugging an engine (either old or new) is to downshift to a lower gear where the engine runs more freely, and the transmission assists the engine in delivering peak power to the rear wheel.
Source

'nuff said...  [moto]

[abby normal]

plain bearings need lots of relative speed (rpm) to develop pressure to support the piston loads.  
do the math and you'll see that oil pressure as supplied by the pump is insufficient ... the real
pressure comes from the shear which, effectively, jams the oil into the narrow gap.  slow the engine
too much and rotating parts will come into contact.

[leonardc9]

plain bearings need lots of relative speed (rpm) to develop pressure to support the piston loads.  
do the math and you'll see that oil pressure as supplied by the pump is insufficient ... the real
pressure comes from the shear which, effectively, jams the oil into the narrow gap.  slow the engine
too much and rotating parts will come into contact.

Thanks guys -- this is useful. I assume this would cause jerking then in both my car and motorcycle engine?