After I bought the B-17 saddle I needed to inrease the height of my seatpost (for my 1999 rigid MTB), and I have playing around with the height of the seatpost a little bit just today again. I just now discovered that my seatpost is further out than it should be (I guess) by about 3/4 of an inch. There was a line that looks like it indicates the max height. Has anybody had any real-world experience (for our type of commuting riding, not jumping off of rocks) with going outside the recommended range. Is there
someway to see if the seat post is holding up? Or do I need to buy a new (longer) seat post.
Thank you for any advice.

You can damage the frame and/or hurt yourself (with the seatpost 3/4" above its design limit). Assuming the frame is a good size for you in the first place, it should be no problem finding a suitable longer seatpost.

There is reason that range is there, above that and you can be torquing the seat tube causing damage that you wont notice until one day it fails, putting you at risk and perhaps ruining your frame.

At a minimum it should extend below the bottom weld of the top tube/seat tube connection. Sure you might get by with it as it is, but I'd recommend being on the safe side, It's not a big deal, just buy a longer seatpost. It doesn't have to be expensive but the consequences of running a too short post might some day be.

The seat post is not only supposed to be in to at least then the maximum height. The post need to be below the joints of the seat stays/seat post/top tube.

(disclaimer I quickly found these photos to help make my point. They link to were they came from.)

The Post needs to he bellow any of the points in the frame were it is joined together. I hope this might help. There is no seat stays on the bike but it still applies. The post should be bellow the the joint. It helps combats any leverage put on the frame with the seat post. This post should be farther in probably then what they are showing.



Or this might happen. I believe you can see the bottom of the post in the crack,(the silver bit in the left. It was not below the joint.

Save your bike just get a longer one.

I had the same problem. I recently got back into biking and am using a nice old Fuji S-12S Ltd that is a little small for me. So I had the seat post set about 1" over the max setting at first. Once I realized it, I bought a much longer post at the LBS for about $18. Now no worries about cracking the frame, like in the picture posted by amckimmy

Wow you guys know how to make a compelling point.

Ok new seat post it is.

Thanks.