cracked frame.

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February 08, 2012, 10:55:04 PM

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Total Voters: 252

[domino0]

about 35mm below the bottom of top tube

This is getting confusing, im confused that is what it is, and yes i work on my own bikes and am good at it, and no i dont work in halfords, the way you worded it and what u said next etc kinda confused me a bit i think, not myself tonight dont think 

[Steve P]

ok, you are meant to have about an inch and a half or more below the top tube

hmm fair enough, still i wouldnt have said 35mm was enough, if thats i wat u are saying is in the seat tube when you are road riding

Do you know how much difference there is between 35mm and an inch and a half?  About 3mm.  No  one measures their seat tube position that accurately.  Effectively stubs69 is saying that, occasionally, he has his post where you have said your limit would be, and then you tell him it's not enough. 

In a previous post Iain said he thought the MIN mark should be where the top tube joins the seat tube.  I'm not sure if that's 'recommended' advice or just Iain's opinion.  I don't remember any lengths being mentioned, and interestingly, when I looked for Iain's post, I couldn't find it, despite being quite sure where it was.  Have you been deleting, Iain? 

Anyway, stubs has 130mm (over 5" to you, Dom) of insertion and that should be enough for anyone 

[iain1775]

Your not quite right on that either what about frames that have an interrupted seat post or a suspension pivot that stops the seatpost going down very far you would never get the post down far enough to get the minimum insertion mark below the top tube. Also if you had a Thompson layback post you wouldnt get it down far enough and if there is one company thats keen on safety its thompson.

Dom is mis quoting me here, I said that refering to one specific incident that was posted on here and regarding that specific model of bike

[mc]

The general guide is that the bottom of the seat post should be below the lower side of the top tube.

The minimum insertion marked on a seatpost is specific to that seatpost.
It's the minimum insertion the seatpost manufacturer recommends to prevent damage to the seat post.

I've previously cracked two frames due to not having the seatpost in far enough, but I've never had any problems since ensuring the bottom of the seatpost is at least 5mm below the toptube.

[domino0]

ok i said sorry, and yes iain ok sorry, i misunderstood you