Mechanical Monday: Quick Tips for a Stuck Seatpost
A stuck seatpost is never fun, especially when you want to change the height of your saddle, lend your bike out to a friend, or take the seatpost out for packing. Obviously, the best treatment is to give the inside of your seatpost a light treatment of waterproof grease to ensure that the metal doesn't bond.
But let's say it is too late for that. Conventional wisdom suggests using heat if the sheer force of you and your friend are not enough to pry the seatpost from the seat tube. In reality, this completely depends on the kind of seatpost you are using.
Have a carbon fiber seatpost with a steel or aluminum frame bike? You're in luck. Using a hairdryer around the seatpost methodically on all sides will expand the metal. Concentrating the heat in one area, however, may damage the paint on the frame.
If you are using an aluminum seatpost, however leave that hairdryer or heat gun in the closet. Want the nerdy explanation? The thermal expansion coefficient of aluminum is 0.0000222 meter/meter kelvin while steel sits at 0.000012. What does that mean for your bicycle? If you try and heat up your frame, your seatpost is going to expand much more than the frame, making your job even more painstaking.
The better solution is using a WD-40 or a liquid wrench on the post first to attempt to free up the corrosive chemical bond. If you really want to play with temperature, though, try sticking with the cold instead. The expansion of aluminum under heat is true in reverse: it will shrink more than steel. If you feel bad leaving your bike out in the winter air, you can go get some dry ice and target that seatpost instead of both the post and the frame.