Mountain Biking - how crucial is standover height on a mountain bike (if everything else fits)?

I'm 5'6" with a 29" inseam and a background in road cycling. I'm interested in a used mountain bike with an 18" frame. When I stand flat-footed over the frame, I'm comfortably straddling the top tube, but there is basically no clearance. I can adjust the saddle to a proper height/angle to be comfortable while pedaling, and the top tube doesn't seem too long because I don't feel stretched out in the cockpit while holding the bars. I realize that I won't be in the saddle all the time while riding offroad (unlike road cycling where I'm in the saddle 99% of the time), so how important is standover height on a mountain bike? Should I pass on this one and keep looking for a smaller frame?

i would say it is pretty important if you are riding technical trails

im going to assume your male...so i ask you this question. how important are your testicals to you?

you have a background in road, which is great, but when buying a mtb you usually want to get a smaller frame than you would if buying a road bike. for the simple reason that trails are not flat. there are dips and ruts that when you have to bail or step down will be lower that flat terrain causing you to smash your boys on the TT.

so to answer your question...yes pass on the frame/bike and find one that gives you ~2" on standover clearance.

Yes, I'm a male. Thanks for the advice, I'll pass on this bike and look for a 16" frame.

Yeh be on the safe side, get the 16" frame and keep your testicles.

Yes, I'm a male. Thanks for the advice, I'll pass on this bike and look for a 16" frame.

yes, i am 5'8"+ and i like the geometry and feel of this 16.5" ... it works for me on trickier, slower technical trails...

I'm a lady, well female at least LOL, and it still hurts, just not as much, so definitely get a smaller frame than you need. Also makes the bike more "chuckable" in corners and stuff i find...

My first MTB (1996 Fuji Suncrest) was too big. I didn't make that mistake again.

I'm a tick over 5'6" with a 30" inseam. I prefer an 18 over the 16.

how important is standover height on a mountain bike?

Depends. Are you a boy or a girl? If the former, how much do you like your sex life?

As people have already done this joke I'll be somewhat useful and add that I find a lower top tube makes it possible to apply much more "body English" to the bike, if that's the correct Americanism.