# Can I use a shorter seatpost?



## redline09 (Nov 21, 2009)

Hey everyone,
The current seatpost on my Fuji road bike (54 cm frame) is 300mm in length, which is plenty long enough -- lots of post left below the minimum insertion point.
Could I use a 250mm post?
I found a post of that size, with more setback and it's a lot more adjustable.
Many thanks for your help with this.
Ride safe.


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## PJ352 (Dec 5, 2007)

redline09 said:



> Hey everyone,
> The current seatpost on my Fuji road bike (54 cm frame) is 330mm in length, which is plenty long enough -- lots of post left below the minimum insertion point.
> Could I use a 250mm post?
> I found a post of that size, with more setback and it's a lot more adjustable.
> ...


If your bike was OEM'd with a 330mm seat post I suggest contacting Fuji support (either directly or through the LBS's rep) and asking that question before purchasing.


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## Hank Stamper (Sep 9, 2009)

PJ352 said:


> If your bike was OEM'd with a 330mm seat post I suggest contacting Fuji support (either directly or through the LBS's rep) and asking that question before purchasing.


??? Maybe I'm missing something but unless Fuji makes the seat post and knows how high this guy needs it I don't think they'd be of any help.

Wouldn't the min insertion line answer this question?


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## PJ352 (Dec 5, 2007)

Hank Stamper said:


> ??? Maybe I'm missing something but unless Fuji makes the seat post and knows how high this guy needs it I don't think they'd be of any help.
> 
> *Wouldn't the min insertion line answer this question*?


I don't think you're missing anything. Other than my suggestion for the OP to contact Fuji, we're essentially saying the same thing. I've never dealt with Fuji's support, so you may very well be right that they'd be of no help, but IMO they should be a resource. 

It's not the manufacturer (of the post) that matters, it's the amount of unexposed post that's required. In this instance, saddle height is a constant, so if you shorten the post by 8cm's the minimum insertion line changes, leaving the possibility that the 250mm length is insufficient. Granted, someone other than Fuji (or the LBS) would be able to assist the OP with that.

An alternative for the OP would be to measure the exposed section of his current post and see if the min. insertion line on the new post would be below that, but given an 8cm difference, I think s/he should seek guidance from a professional before purchasing.


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## Mike T. (Feb 3, 2004)

Redline there is a seatpost rule of thumb - the post MUST extend down into the frame at LEAST to where the underside of the top tube intersects the seat tube. Then all the strain isn't on the top tube/seat tube junction. And to be safer I'd go an inch longer than this too.

Easton, for their seat posts, says this - "For frame durability, ensure the post is inserted past the bottom of the top tube."

Thomson says to insert "so that it sinks below the top tube." Here in fig. 7 -

http://www.lhthomson.com/docs/seatpost.pdf


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## PJ352 (Dec 5, 2007)

Mike T. said:


> Redline there is a seatpost rule of thumb - the post MUST extend down into the frame at LEAST to where the underside of the top tube intersects the seat tube. Then all the strain isn't on the top tube/seat tube junction. And to be safer I'd go an inch longer than this too.
> 
> Easton, for their seat posts, says this - "For frame durability, ensure the post is inserted past the bottom of the top tube."
> 
> ...


You (and the manufacturers mentioned) aren't taking some important variables into consideration. For instance, the fig. 7 diagram shows a bike with compact geo (sloping TT), so when they say make sure the post drops below that point, it's essentially 1/2 way down the seat tube. If you take that same advice at face value and apply it to a frame with traditional geo (horizontal TT), it means that the seat post extends approx 4-6cm's into the seat tube - clearly an unsafe condition. 

The advice seems geared more towards preventing frame damage (admittedly, a worthy goal) but disregards a combination of other safety related factors, such as rider weight, the amount of exposed seat post and minimum insertion line - all in all poor advice as written, IMHO.


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## millennium (Apr 3, 2002)

My answer: Make sure seat post will insert past the bottom on the top tube, or past the minimum insertion line on the seat post, whichever gets you the furthest insertion. There might be some other factors, but to me, the prior sentence is the starting point.


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## Mike T. (Feb 3, 2004)

PJ352 said:


> You (and the manufacturers mentioned) aren't taking some important variables into consideration. For instance, the fig. 7 diagram shows a bike with compact geo (sloping TT), so when they say make sure the post drops below that point, it's essentially 1/2 way down the seat tube. If you take that same advice at face value and apply it to a frame with traditional geo (horizontal TT), it means that the seat post extends approx 4-6cm's into the seat tube - clearly an unsafe condition.
> 
> The advice seems geared more towards preventing frame damage (admittedly, a worthy goal) but disregards a combination of other safety related factors, such as rider weight, the amount of exposed seat post and minimum insertion line - all in all poor advice as written, IMHO.


Only a mental case would NOT put a post in at least down to its minimum insertion line. I think the seat post experts (Thomson & Easton here) kind of assume that. Otherwise they would have to ship a service mechanic with each post.


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## PJ352 (Dec 5, 2007)

Mike T. said:


> Only a mental case would NOT put a post in at least down to its minimum insertion line. I think the seat post experts (Thomson & Easton here) kind of assume that. Otherwise they would have to ship a service mechanic with each post.


Many people assume - that's partly my point. Noobs (and consumers in general) assume what's written is fact and proceed accordingly, thus my statement_ "all in all poor advice as written"._

Your 'experts' may build well designed bike components, but IMO in this instance both you (and they) have provided misleading (and potentially unsafe) statements, thus my response.


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## Mike T. (Feb 3, 2004)

PJ352 said:


> Many people assume - that's partly my point. Noobs (and consumers in general) assume what's written is fact and proceed accordingly, thus my statement_ "all in all poor advice as written"._
> 
> Your 'experts' may build well designed bike components, but IMO in this instance both you (and they) have provided misleading (and potentially unsafe) statements, thus my response.


Don't you think they DON'T have the "insert post to at least the min insertion line" on their sites and in the instructions with the posts? Of course they do. I just typed the minimum for my posts. It's all there. I can't believe you wouldn't know or think this. I wasn't pretending to be a stand-alone instruction manual for the OP.


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## PJ352 (Dec 5, 2007)

Mike T. said:


> Don't you think they DON'T have the "insert post to at least the min insertion line" on their sites and in the instructions with the posts? Of course they do. I just typed the minimum for my posts. It's all there. I can't believe you wouldn't know or think this. I wasn't pretending to be a stand-alone instruction manual for the OP.


I said many people assume, but didn't say that I do. I based my responses on the material and opinions you supplied, not what I thought or assumed. In retrospect, I'm glad I did, because IMO in doing so some points have been clarified for the OP and others. 

To the OP: Apologies for the slight diversion, and I stand by the advice to seek professional guidance before purchasing. Ride safe! :thumbsup:


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