Seatpost length??

hoakin1981

Fellow riders, as shown in the subject line my question is about the seatpost length. I am looking to built my first road bike so now that i am in the market for a seatpost i noticed that there are 2 main lengths available, 400mm & 300mm with the latter being a little pricier. Provided that the frame's vertical tubes can accomodate both lengths with no problem why go for the 400mm and why for the 300mm? I am thinking seatpost - saddle height is the main factor to consider, in this respect if based on the frame i got & the seat height i am planning to use i could use both lenghts which one should i go for?

Many thanks in advance for all replies & MERRY XMAS TO ALL!

rake

select one that leaves pleanty of seatost in the tube, pleanty more than minimum insertion marks imo. never mind about an extra 20g in weight.