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Sizing-Potentially stupid question regarding seatposts?(5 posts)

Sizing-Potentially stupid question regarding seatposts?funknuggets
Jan 2, 2003 11:23 AM
I know this is likely the most mundane and laborious discussion regarding cycling... the dreaded fit issue.

Im just curious, is there a point at which there is simply too much seatpost exposed? I know the whole compact geometry movement can skew this, but on non-compact designs, other than the maximum limit line on the post, is there a point at which it becomes obvious someone needs a larger frame? Or, conversely, if someone buys a bike, but only has like 1 or 2 inches exposed but is otherwise decently positioned, should they have gotten a smaller bike? Im looking for a % of seat tube or x cm is too much/litte...

I realize there will be impacts as to how the rider is balanced in relation to their hands and relative height of the handlebars, but putting that aside are there any "rules" of the road as far as seatposts go?

One last question. Is there any importance to standover height other than comfort when standing still? Should it be an important factor in determining whether a bike "fits" you?

Thanks in advance
Traditional vs. contemporary thinking (I'm a traditionalist)cory
Jan 2, 2003 11:48 AM
The old rule for seatposts used to be that you should have about a fist full showing--close your hand around the post with your little finger touching the top of the seat tube, and your fist should just cover the post.
As you can tell by looking around, that's widely ignored these days. I see people with eight inches of exposed post all the time. But when I set up my new bike, I sized the frame to work that way, and it's REALLY comfortable. A larger frame also makes it easier to get the handlebars up, where (again, traditionally) they belong.
As for SO height, I'm 6'4" with long legs, so I've never had to think about it. But you do want enough clearance so if you have to hop off the saddle, you don't squash The Boys....
My custom frame was built "traditionally"...Stinky Hippie
Jan 2, 2003 2:03 PM
...which has meant that I have a little more than a fistfull of post and a half inch of spacers using a 110 mm stem with a 5 degree negative rise --- all of which produce about a two-inch drop from saddle to the top of my bars. Sometimes I think that I would have been happier with a little more standover (I get about 2 inches) and a little more of a saddle- to bar height differential, but my setup has meant I never feel like I'm putting any excessive weight on the front end while standing on steep grades , and I feel much more confident during descents.

I think the trend toward smaller frames, more exposed seatpost etc. has alot of us (including myself)rethinking our setups for lthe wrong reasons... Yes, or maybe I'm just trying to justify the design of my custom frame:)

Feel the gin
Some of the fit esoterica makes it all seem harder than it is.bill
Jan 2, 2003 12:02 PM
These are the considerations:
Standover. You don't want to hang your jewels on the top tube. Not a whole lot more to it.
Exposed seatpost. The real consideration here is two-fold. One is common sense and the other is a bit overblown.
One: You want to be able to have enough drop or little enough drop to the handlebars to be comfortable on the bike. Because you can't get your handlebars any lower than the headtube plus headset height, and you can't raise the bars indefinitely, either, you need to have the proper differential between the saddle height and bars to get you into the aerodynamic position you want. For some riders, this is 6 inches, with lots of exposed seatpost. For some, the saddle and bars are more or less even, which means little exposed seatpost and maximum extension on the stem spacers or riser stems or stem height or turn of the bars or whatever other trick or device you care to use.
Two: traditionally, racers used the smallest frame they could get to work as a way to maximize stiffness, minimize weight. I think that other design considerations easily can outdistance this wisdom.
And then you have to get the top tube to fit. Too small, and your saddle is pushed all the way back. Too big, all the way forward. Centering on the rails is most pleasing, aesthetically, and probably gives you a little more comfort. Some people believe that the position of your knee over the pedal spindle at 3 o'clock is critical -- I'm still working through that one. Even here, stem size can make a big difference, but you want your stem to be probably in the 110-120 range for handling purposes. If you want a certain bike, and you need to have x toptube length, you're going to have y seatpost exposed.
And then there are aesthetics. More seatpost, even with a few stem spacers, makes your bike look more aggressive, and vice versa.
There are lots of ways to make a bike fit. If you get within about 2-3 cm of ideal, maybe more, you can make it work pretty easily.
all this by way of saying, other than what you already knew,bill
Jan 2, 2003 12:49 PM
for my money it's a fashion thing. Assuming that you are comfortable with the drop, two inches of seatpost looks like a touring bike, 6 inches -- like a racer.