Originally Posted by Tequila Joe
How to know? When the brake tabs, drop outs or stancions snap when you are flying down a hill, you will know....
Simply pain....lots and lots of pain hahaha
Its usually pretty obvious actually. Forks rated "xc" or "trail" forks will not support 8in without some risk. Fr and dh forks, usually good to go, all mountain would be the only confusing ranking, but really I would assume they would be fine. Pre 2002 these rules change a bit as the ratings were different and 20mm and 8in in general were not common.