Mountain Biking - Why seat tube clearence is so important?

Why is the 1 or 2 inches of clearence between your crotch and the seat tube so important?
I mean why 1 or 2 inches. If withthe saddle you will have no clearence even it is all the way down.
I am 6.1 and my inseam is 34". Should I go with a 19" or 21" frame?
Thanks

so you dont nut yourself when you slip:crash: :crash: :crash: :crash: :crash: :crash: :crash: :crash: :crash:

I know that. What I mean is that the seat tube measurement is not necesseraly the height of the horizontal bar of the frame.
SO, that is the only reason?
It has nothing to do with with ability to maneuver?

Originally posted by PeterG1185
so you dont nut yourself when you slip:crash: :crash: :crash: :crash: :crash: :crash: :crash: :crash: :crash:

Well put! :p

One of the big reasons for getting some space between the top and tube and the crotch is to give some space in the case of a fall. If you have ever fallen onto a top tube at speed, you know why it is important to leave some space. A smaller frame will also be slightly easier to maneuver over real technical terrain, and will be easier to handle in general because of its smaller size. A slightly bigger frame will be a bit more stable at speed because it is larger, but may be a little harder to maneuver underneath yourself because of its larger size. With some practice, though, you can get used to either. Most people would go with a smaller frame. I tend to like larger frames and handle one as well over technical terrain as anyone I ride with. A good LBS will be able to give you some suggestions as well.

-Moab

PErsonal preference. I have a good 4 or 5 inches between me and the top tube...why? Because I need my dangly bits protected when I do drops and jumps. If I was PURE xc...then I wouldn't worry about it so much but I fall...and the more clearance I have the better chance I have of producing babies...

I just tried both sizes again. The 19" gives me more clearance, but I don't think my position will be healthy for long rides. The 21" feels beter, but I maneuvering will be not that easy on the trails.
Would 1" clearance be enough?

Do you do more epic rides or technical short rides? Depending on which you do will be your decision breaker.

Based on your measurements, I would say the 21" would be a good choice. It's kind of strange that you only have an inch of clearance, but my bike has a sloping top tube, so it could be different. You will not notice much of a handling difference on the trail - at least not enough to make you go with the bike that doesn't feel as good. When I mentioned that it might be a little harder to handle a larger frame, I didn't mean it would be a dramtic difference. Some people just feel that a smaller frame is easier to move around over and easier to shift your weight over for technical terrain. I ride a 21 inch frame and both of my friends ride a 17" and a 19". Last season, I could out-maneuver both of them in nearly any technical situation. The person with the most practice riding at a slow speed and over technical terrain will be the better bike handler no-matter the frame size. If the 21" feels better, have no reservations about buying it because of bike-handling. It alll comes with practice.

-Moab

It is a long time I don't ride. But I used to do a bit of everything. Sometimes, just like adventure ride, XC. Sometimes straigh steep tracks, an dother times just downhill.
As for now, I am not sure what I will be doin the most. Cause I just moved here and have'st bein griding at all.

Moab, my heigh is 6.1 (1.86m) and my inseam 34"(86cm) .
If you guys want to check the geometry it is in

http://www.giant-bicycles.com/us/catalogue_popup.asp?sPageID=popup&popuptype=geometry&geometryid=10635

It is bad that they don't tell what is the standover height!?

I had knee problems in the past (sprained), is the bike size going to influence on that?

Skuba,

Your knee problem can be taken care of with adjustment of the seat and setpost independanlty of the frame. By raising or lowering the seatpost, you can adjust based on where you might be experiencing pain. Clipless pedals with more "float" might help when you get to that step, and various other things can be experimented with to see if they help. Knee problems shouldn't be a concern when picking out a frame - just make sure the seapost cann safely compensate for the size of the frame (e.g. - not coming out past the limit mark to raise yourself up high enough.)


-Moab