Mountain bikes with 500 TTT?

[Catrin]

You need to be looking at effective top tube length, what the top tube would be if it were horizontal.

Remember mtn bikes do not have to fit to the mm the way a road bike should, at least assuming you're not going to plant your butt on it and ride it like a road bike. You move around so much more and it is such a more dynamic activity that you won't notice the 1 mm differences.

I was wondering this, thanks! The differences are quite large though perhaps 25-35mm won't matter. When I am ready I will discuss this with my fitter. I won't know until the mountain bike clinic if my hands can handle it or if my skills have progressed enough to take on beginning mountain biking this year. I WANT to, but I don't want to set myself up for failure by taking it on too soon...