TIGER AND BEAR From tiger expects books. Tigers are not very courageous, they generally attack by surprise...

TIGER AND BEAR
 
From tiger expects books. Tigers are not very courageous, they generally attack by surprise by the back. First  lets make things clear. Siberian killing by the back adult brown bears are rare and it is on adults females or cubs. Secondly brown bears did killed tigers and steal the tiger's food too. In frontal attacks with serious opposition tigers in general don't do too well and tend to retreat rapidly when its too tough or see they can't win.  Tigers running from lions are numerous but when a tiger as not the advantage of surprise again a bear even smaller than them they often not very successful.  On the first example a tiger ran away from a sub adult grizzly after a face to face battle. We have to take in consideration it was a captive tiger (perhaps taken from a scene from a movie) not a wild but the determent bear was still a sub adult. As we see with lions the tiger tried to escaped from the bear too.   
 
TIGER VS YOUNG BROWN BEAR FIGHT.
http://videos.transcendense.com/grizzly-bear-vs-tiger-fight-ultimate-fighter-revealed-video_e73571f1a.html
 
Two TIGERS FIGHTING A SLOTH BEAR with no element of surprise.
https://www.youtube.com/watch?v=ysNa_YQFwiM  
FROM WCS RUSSIA (wildlife conservation society)
 
Physical appearance:
 
Siberian tigers are often considered the largest of the tiger sub-species, although they are in fact about the same size as the Bengal tiger. An adult male usually reaches a body length of 2 meters, with his tail adding another meter. Average weight for males is 160-190 kg (353-419 lbs), while females are smaller, weighing in at 110-130 kg (243-286 lbs). The largest male captured for scientific research under the Siberian Tiger Project weighed in at 206 kg (450 lbs).