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trimming your seat post(13 posts)

trimming your seat postraleigh rider
Mar 1, 2003 4:24 PM
I've read that cutting the length of your seat post can eliminate weight. What's the max that can be cut, or how much should be left to go into the seat tube? What happens if you cut too much off?
Probably one of the cheapest ways to save weightSprint-Nick
Mar 1, 2003 4:36 PM
Its probably one of the cheapest ways to save weight. Keep in mind you may only save 50 grams though. To answer your questions.

What's the max that can be cut, or how much should be left to go into the seat tube?
Normally seatposts will have a max extension line. So measure the distance from the end this, mark where your post leaves the seattube and measure down from this. For safety maybe add 1/2-1 an inch.

What happens if you cut too much off?
Nothing or everything. The max entension basically is the safe limit (not sure how its determined) to have your seatpost in the seattube. Any less and you may not have enough material to stop it from breaking. Its an all or nothing thing since a seatpost failure is almost 100% catastrophic in it just snaps.

20 gm, max savingsKerry
Mar 1, 2003 4:45 PM
The amount you can cut depends totally on the length of your post and how much you have exposed. Typically, a post is marked for minimum insertion with a line or lettering or something. That tells you how much you need to have in the frame (usually about 2 inches/5 cm). Seat posts are very light per length, so your savings will be tiny from cutting some off, and you will lose the flexibility to raise your saddle if you want to change position in the future.
20 gm, max savingsrussw19
Mar 1, 2003 5:19 PM
Most of a seatpost's weight is at the clamp. Not the post. So cutting it won't do much. Don't bother, save the weight somewhere else on your bike. Save weight on rotational mass if you can, worry about static mass later. Go for a lightweight set of tubes, tires, and rim tape before you start cutting parts to save a few grams.

Mar 1, 2003 6:58 PM
Like Russ said most of the weight is at the clamp. And although it is free (granted you have a hacksaw) way to save a few grams its not worth it unless your going up Mont Ventoux.

re: trimming your seat postMR_GRUMPY
Mar 1, 2003 6:42 PM
If you got a great deal on a mountain bike seatpost it would be a very good idea. If you cut it off too short, you might cause the top of your seat tube to bend. If I remember correctly, you need at least an inch below the bottom of the top tube.
re: trimming your seat postrussw19
Mar 1, 2003 7:07 PM
And if it's an aluminum frame, you want to go an inch below the cut in the seat tube. You know, the little slot at the back by your seat clamp... go at least an inch past there.

Now if this is post is a 400mm MTB post and you have 5 inches in your frame, sure, cut it, but if it's to cut 1/2 an inch to save 10 grams, why bother... cut too short and you screwed up for what? 10 grams.... That's my take on it.

re: 1" below little slotcyclopathic
Mar 2, 2003 2:28 AM
actually you wanna go 1-1.5" below weld below seattube/top tube junction. keeping seatpost shorter puts to much stress and may cause welds crack.
1-1.5 inches is too littleFez
Mar 2, 2003 10:44 AM
If you want to clear the seat tube welds on most road frames, you would need a post that dips in at least 2.5 inches (approx 6.4cm).

That is for most road frames. Keep in mind that a raised seat collar adds another 1-2cm of distance from the top of the collar to the bottom of the welds.

FWIW, The max insertion line on a 27.2x250mm long Thomson post is 2.5 inches, and just for safety, I would always leave more post than that inside.
1-1.5 inches below TT weldscyclopathic
Mar 2, 2003 4:22 PM
it roughly comes to ~3" from top and that's what minimal insert is usually marked to. Sorry if I wasn't clear in previous post
Only if absolutely necessaryFez
Mar 1, 2003 10:00 PM
Like if you have a mtn bike post (330mm) or an extralong (410mm) seatpost and you have a conventional geometry road bike. These posts are so long that the waterbottle boss might interfere with the insertion.

Only then would I cut it. Why bother otherwise? Saving 20 grams or less is not worth the hassle.
Another considerationDERICK
Mar 1, 2003 11:01 PM
If you ever want to sell the bike or change parts to a new frame that short seatpost may be a problem. I was considering cutting my new carbon fiber post but changed my mind. The post was expensive and cutting it would bring the value to zero if I ever wanted to sell it.(I do a lot of E-bay) I don't think you would notice the weight savings anyway.
I have agree with rider
Mar 2, 2003 5:49 AM
cutting the post may not be worth the problems later. I cut a post once to save weight. Th rule is 3 inches from the point where the post is shown out of the seat tube (4 is better). I usually get bikes that need longer post so that's how I determine if I need a 350 or 410 post instead of the stock 330 on my mtb.

You could crack your frames seat tube clamp area if it's too short. The manufactor won't warrenty your frame if that happens. That's why the LBS tells me to get a longer post when it's only 2 inches in the seat tube.

I think i remember doing this to a KHS bike I used as a commuter. I put a longer post on and the thing quit creaking on me. MY seat gets set all the way to the back on the post, so I put alot of leverage on the seatpost. I think having more in the seat tube helped with that problem.