i have been trying to read up on frame geometries. it is interesting how different frame sets and different lengths of forks affect riding. i was wondering if somebody could give me a first hand knowledge base about stuff like this. the basics i guess. how the length of the top tube affects comfort positions, the angle of the seat, the angle/length of the stem (the short tube that attaches the headset to the handlebars, is that called a stem?), yknow stuff like that. for the most part i notice XC based frames have the frame in a diamond sort of shape whereas the freeride aggressive frames are more triangular. that is the angle of the top tube and seat stay flow into each other in the latter frames and in the XC frames the angles differ. how the heck do these differences serve different riding purposes? how would a very short stem affect steering? ah i guess it is impossible to tell it all to me but i just wanted some sort of basic know-how so i could figure things out a little bit. i have a trek 6500 and the frame geometry is pretty different from the specialised xc bike but the giant ones (iguana) seems more like the trek. im basically interested with trail biking that can also do some aggressive-on-the-bike stuff like a few drops, probably not more than 3 feet yet though. i bought a trek 6500 because thats all they had and although im riding it anyway i feel like i was just wondering if i could figure out what the intents and the limits of my bike geometry are. also, well there is no way i am going to upgrade anything on my bike until something breaks i have also been wondering about stuff like is it okay to put a 130 mm fork on a bike that came stock with an 80 mm one? i have never seen a fork other than my own so im wondering how they adjust the larger travel into the length cuz if the length of the fork increases the angle of the bike will too. anyway, just some basic stuff like this. a link would be very helpful too of course. im just more curious than anything else i guess, its interesting stuff..