Hello all, i just have a few questions i would like to ask. Basically i am grinding my own rim tomorrow for the first time, i have watched the TNN and Tartybikes videos on rim grinding but they both do some things different, so my questions are: 
 
Do i fully remove everything so i just have a rim, or shall i grind my rim while it's sill on the bike? My main concern is cutting into the tire some how? 
Is there a lot of drag when grinding i.e. will my angle grinder feel as if it wants to pull away? 
How will i know when i have ground my rim well enough? 
Do i even have to grind my rim for TNN LGM pads on a rear magura? Or is it better to leave it? 
How long will my grind last if i ride 4 days a week? 
What disc shall i use? 
For a sharp medium grind shall i use a thin disc at about a 45 degree angle, this is what TNN suggests you do? 
 
I am going to be running a rear magura with TNN LGM pads if this makes any difference, TNN say i should do a sharp medium grind for best performance, both videos i have referred to can be found below. 
  (TNN)
http://www.tartybikes.co.uk/media.php?group=guides&id=2 (Tartybikes) 
 
If you wondering what rims i have, well there stock Saracen rims on my mod so i think they are both 20", that as much as i know about them. 
 
Thanks 
 
EDIT: My dad is certain that this will ruin my rim, don't ask me why, is it just him being stupid? He doesn't even know what a trials bike is, hes just had experience with motor bikes and old mountain bikes lol