Seatposts ship long and can usually be cut down. But how much can you cut? And should you cut? This article will tell you when and how much to cut.
The short answer is that a standard seatpost can be cut, but should extend at least 5″ (13 cm) into the seat tube AND at least one inch (2 cm) past the top tube intersection. Cutting excess length is not absolutely necessary, but useful in that it saves weight and reduces the likelihood of jamming.
|CUT SEATPOST||UNCUT SEATPOST|
+ lower weight
+ less jamming & corrosion
+ safe with 5″&1″ rule
– less interchangeable
– too short unsafe
+ resale value
+ always safe
– more weight
– may jam
– may trap water
How short can I cut the seatpost?
You can cut as short as you wish but make sure there is a sufficient length of seatpost in the seat tube.
General rule: The general rule is that the cut post, when installed to the correct height, should:
- Extend at least 5″ into the seat tube, AND
- Extend at least 1″ below the top tube intersection
Use this rule for standard aluminum posts and metal frames. This rule ensures the rider’s body weight is transmitted from the seatpost to the seat tube without causing too large stresses on the parts at the joint.
What about minimum insertion length?
Some seatposts have a minimum insertion length marked on the tube. This length is the minimum for the post and should be respected. However, your frame may require more insertion – make sure you adhere to the general rule above.
Extra inches, just in case
In most cases, it makes sense to leave the seat post a few inches longer than the minimum.
A few inches of extra length makes sure you are on the safe side in terms of frame strength. It also leaves you some margin for a different saddle height, saddle model or a slightly taller rider.
The weight penalty from the few extra inches is not an issue unless you are racing. This length will also not make the tube much more likely to jam due to corrosion.
Should I cut the seatpost at all?
Cut the seatpost if grams are a priority and you are not going to swap or sell the post; otherwise you may be better of with an uncut post.
A long, uncut seatpost is more versatile than a cut post. A full-length post works with your bike, but also any other bike frame & rider combination. This gives you the option of selling the post or using it in another frame.
A cut seatpost is optimized for the frame and rider. It takes realizes all possible weight savings and is also less likely to jam in the frame.
How to cut the seatpost?
A standard aluminum seatpost can be cut with most common metal-cutting tools:
- Hacksaw or reciprocating saw
- Rotary multitool (e.g. Dremel)
- Oscillating multitool
The cut does not have to be very clean as long as you deburr and chamfer the end with a file after cutting. This is so as to reduce scratching inside the seat tube.