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Discussion Starter · #1 ·
I'm a lightweight at 150 lbs, but I ride a somewhat delicate magnesium frame that has been known to break at the seat cluster under certain circumstances.

I use a P-2 Moab suspension post with a parallelogram design that allows the saddle to sag back and down under load. (The post is long out of production but was perhaps one of the better ones ever made at 394 grams and fully damped.)

My theory is that with the suspension post taking the hit, stress at the cluster welds is greatly reduced.

Parallelogram suspension posts currently available are the Thudbuster and Tricky Dick designs.

Would it not be practical for heavier riders to use such a post if they are riding a hardtail with several inches of seatpost showing and therefore have increased leverage/load on vulnerable seat cluster welds?
 

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interesting... moving seatpost.....

Something tells me that my 240 pounds of XC fury would feel rather, um, unsure ontop of a floating seat. Of course, there is always the chance that I would just force the seat to remain at a flexed position (she can't take na mor capitan!!)...

Most Clydes I know don't have to worry about the cluster welds since we tend to lean towards bikes that don't fall in the "somewhat delicate frame" catagory you describe.
 

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Of all the frames I have busted

it has never been the cluster welds that have busted, usually the cracks appear at the crank or where the head tube is. Methinks that if you are busting those welds you had should probably be standing a bit more, but of course I am a total pansy when it comes to pain.
 

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Discussion Starter · #4 ·
CactusJack said:
Methinks that if you are busting those welds...
I'd be pretty impressed with myself if I could ever break a frame.

I wonder if I can sneak this into Women's Lounge with a change of wording and get some positive feedback.

Thanks, guys.
 

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BadHabit said:
I wonder if I can sneak this into Women's Lounge with a change of wording and get some positive feedback.
Apologies, I didn't mean it to sound rude, I have worked at bike shops as a younger person, and haven't heard of anyone having an issue with the cluster welds - even on a road bike, unless it was improper welding due to poor workmanship, but running the type of material you have could pose a problem, I don't know.

For me, a floating saddle wouldn't be a good idea, especially with some of the ones I have seen that can make changing position a bit more difficult for the larger guy. Plus, I wonder if the elostomers that they use would flex too much under the weightier person, as most seem to be designed for the lighter rider
 

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Broken seattube

I have actually broken several frames at he seat tube cluster. The problem, though, was a short seatpost and a tall extended seat tube above the support of the seatstays and top tube. A slightly longer seatpost cured the problem until the frame broke elsewhere. Maybe a suspension seatpost would have saved the frame, but a more likely solution would be the company (long since out of buisness) were no to have included a 330 mm seatpost to save 6 grams.

And I don't know why some of you don't think a susp. seatpost would work well. The bike is virtually identical until you hit a bump while seated. I just looked at the cane creek website and the manual for the thudbuster claims that a particular set of elastomers are designed for people between 215-250 lbs.
 

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Discussion Starter · #8 ·
CactusJack said:
Apologies, I didn't mean it to sound rude, I have worked at bike shops as a younger person, and haven't heard of anyone having an issue with the cluster welds - even on a road bike, unless it was improper welding due to poor workmanship, but running the type of material you have could pose a problem, I don't know.

For me, a floating saddle wouldn't be a good idea, especially with some of the ones I have seen that can make changing position a bit more difficult for the larger guy. Plus, I wonder if the elostomers that they use would flex too much under the weightier person, as most seem to be designed for the lighter rider
No problem; I didn't take it that way at all. I was just joking about taking it to the women's lounge--I ain't that brave.

Yeah--I haven't heard about cluster werlds breaking either except on this magnesium frame (poor workmanship as you say) and for exactly the reason from jimbo below--trying to run the seatpost with a shim that was too short!

It's hard for me to add to anyone's knowledge on these forums!

One thing maybe: I happen to use a seatpost that is field adjustable for sag.
 

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Discussion Starter · #9 ·
jimbo2k said:
That you do not remove that seat tube reducer in your magnesium frame. That is the trick to getting that russian built mag tubing to last. Jim
You know your MiG tubing pretty well!

The first run of these frames was shipped with a reducer that was too short and put stress on some already questionable welds. A longer shim solves it.

Seven years and going strong (Lodestar).
 
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