switch diameter...

the ieee 802.1d standard recommends a diameter for the tree of 7 switches.  this means that any two switches should not be more than 7 hops apart...

the default hello time for the tree is 2 seconds... in other words, if the default hello time was set to 1 second (it can be from 1 to 10 seconds) the bpdu traffic for the tree would double...

knowing that bpdu's at two seconds is already a heavy load for any switch:

als2#debug spann bpdu                                                          
als2#                                                                          
Apr 17 05:47:11: STP: VLAN0001 rx BPDU: config protocol = ieee, packet from Fas
Apr 17 05:47:11: STP: enc 01 80 C2 00 00 00 00 0B 5F C9 00 07 00 26 42 42 03   
Apr 17 05:47:11: STP: Data     00000000006001000B5FC90000000000006001000B5FC9000
Apr 17 05:47:11: STP: VLAN0001 Fa0/7:0000 00 00 00 6001000B5FC90000 00000000 600
Apr 17 05:47:11: STP(1) port Fa0/7 supersedes 0                                
Apr 17 05:47:1                                                                 
als2#1: STP: VLAN0001 Fa0/17 tx BPDU: config protocol=ieee                     
    Data : 0000 00 00 00 6001000B5FC90000 00000013 80010009B752D780 8011 0100 10

setting for 1 second would be unwise...  remember to un all before the debug, then up arrow twice to recall the command and enter,  as a good practice before running debugs... setting hellos for longer will make the bpdu output to the terminal more palatable..

as always, running debugs on a production network is at your risk... you'll need an understanding boss...

changing timers is most effective at the root switch as the timers will then be propagated throughout the diameter...

also changing stp timers is a tricky proposition at best, and not recommended... leave that shit alone...

for stp enhancements, see...

 http://insearchofthecert.blogspot.com/2012/02/guest-post-warren-sullivan.html