My mtn.bike is a '96 (frame), components more modern, so it has "old school" geometry. I find I ride best with the seat as much as 1/2" lower than if I was riding it on pavement. You might ride with the seat higher on rolling, non-technical singletrack than on more technical trails. For me, it was trial and error-I don't have a set seat height- as it might be diff. for diff. trails. But that's just me--do what works for you.