how long is your seat post?
 

Just getting started bicycling. Trying to decide between 56 and 58 cm road bike. I'm 5'10" but with long inseams. I'm aware of many internet sites toget proper bike size and most conclude getting a 56 cm. Trouble is, that leaves 5.25 " of seat tube sticking out. It looks excessive and I just haven't seen that much on other cyclists. What is normal or excessive? Thanks, Joe

Welcome to the forums Joe!

I have about that much out as well, I'll double check the exact distance tonite. Most charts fit me at a 61cm bike, but i felt most comfortable on a 59cm (c-t) Klein Quantum Race. I guess its really up to you, however I would have a competent local bike shop that deals with road bikes fit you. The last thing you want is a bad fitting bike.

My Bianchi Cross bike is 4 1/2" and my MTB is 6".

Two things to remember... (1) It depends on the bike's geometry. Compact frames with sloping top tubes will naturally have more exposed seatpost than traditional frames. (2) The amount of exposed seatpost is relative to the size of the frame. Smaller frames will have less seatpost exposed than larger frames.

There are a whole lot of other variables, like the proportional length of your legs to your torso, and the proportional length of your shins to your thighs, not to tmention crank length, stem height and angle, pedal stack and shoe sole thickness. In other words, there is not set formula for how much seat tube should be exposed.

Typically, the length of exposed seatpost will be about equal to the bike's headtube length on a traditional geometry frame. But this is just typical. Sean Kelly rode for years -- and won a whole lot of races -- with his saddle so low that only about four centimetres of seatpost were exposed. On the other hand, you'll see a good number of pro riders with 15-20 cm, or more showing.

The bottom line is your saddle position, and this the amount of exposed seatpost, relates to the length and extension of your legs and not fashion, aesthetics or the way anyone else does it. You should be looking for about 95% leg extenstion with the crank at the very bottom of the pedal stroke. If you need more or less seatpost to achieve this, then that's what you should do.

Many of the compact road frames (sloping top tubes) seem to have considerably more seatpost than that exposed. As long as the "Minimum insertion" line is not exceeded it should be fine.

Thanks for all the rapid replies, great forum. I forgot about the compact frames. The bike I measured the seatpost on is a Trek with pretty conventional geometry I believe, just so we are comparing apples to apples. Are there a lot of regular cyclists with the post out over 15-20 cm (as was mentioned)?

If this is a non-compact frame, then the height of the top tube controls the height of the head-tube. If you want to get your bars very low, then the smaller frame size is better. If you want the bars higher, the the larger size.
If the top tube is 1" lower, and you have an extra inch of exposed seatpost, it really doesnt make any difference to the saddle position.

How do the frames differ in top tube length. This is the really critical dimension, that will affect your reach to the bars, and the stem length you need.