I don't know when you should do it but I "check" mine about every 7 years or so. I put about 4 to 5K a year on mine. I just take a peak and if it looks good it's good. I have to replace the brakes about every 7 to 10 years or so anyway.
~ Too many freaks & not enough circuses ~
"Life is not tried ~ it is merely survived ~ if you're standing
outside the fire"
"The best way to get a bad law repealed is to enforce it strictly."- Abraham Lincoln