The old "what frame size" question for a mountain bike

[jaybee]

I'm about to buy a full suss bike second hand. Got my eye on a few and will be buying within the next few weeks. I am noticing that a lot of the bikes like Specialized and Trek for example state something like:

Actual 18.5 inches
Virtual 17.5 inches

I get that. I think. So virtual is what it kind of would be if the top tube was more horizontal and traditional?

Thing is, I hear of a lot of people say to buy the smallest frame you can get away with because it's "more chuckable" and controllable over jumps and when mucking about. Is this generally what people do?

I have ridden my mates medium sized Specialized stumpjumper and it feels fine. But then I get on a large and it also feels fine but more stretched out.

I am 6ft2 and lanky build and weigh about 11 and a half stone. I know buying second hand is a gamble, but would you say I should generally look for LARGE frames around 19/20 inch or mediums around 17/18 inch?

Any advice welcome.

 

[TheBrooder]

you need to try a few more if possible, bike geometry differs from one manufacturer to another

 

[semi-pro waster]

As TheBrooder says the only sensible thing to do is to try them, frame geometry tends to be fairly standard within a single manufacturers range but the feel can be wildly different between two bikes that are nominally the same size if they're from different manufacturers. There are certain things you can do such as changing the stem/handlebars/seatpost etc to adjust the feel if it's slightly wrong but if the frame is seriously wrong for you there's not much you can do.