Maximum seat height
06-07-22, 09:35 AM
#26
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Take the post out and learn to ride standing. It's the only way that makes sense for you with this frame.
06-07-22, 09:35 AM
#27
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You know, if you're gonna do it anyway, why even ask people who know much better than you whether you should do something?
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06-07-22, 09:36 AM
#28
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I know a guy who bought an entire bike for a seatpost. It was a very nice seatpost, and he ended up restoring the whole bike. But still.
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06-07-22, 09:43 AM
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06-07-22, 09:46 AM
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06-07-22, 09:49 AM
#31
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It's not necessarily the height of the seat post (thought that is a big part of the lever) as much as it is the amount of post inside the frame to counter (be equal & opposite) the forces of you sitting on the post levering it around.
A foot between the saddle & seatpost clamp with 4 inches of post in the frame equals a 3:1 multiplication. Ergo 200 pounds of you equals 600 pounds trying to blow apart the seattube/top tube junction. Mentally multiply to that 2,3,4g transient loads from potholes etc...You'll see we are dealing with appreciably large forces on relatively thin walled tubing. An inch of post inside the frame with a 200 pound you a foot above is 2400 pounds of bending force. Well over a ton...& that's just a static value. A simple unexpected bump could easily make momentarily well over 10,000 pounds or more lever force trying to pry your bike apart.
Don't be stupid. Get a longer post that at least extends down to below the lower top tube weld.
A foot between the saddle & seatpost clamp with 4 inches of post in the frame equals a 3:1 multiplication. Ergo 200 pounds of you equals 600 pounds trying to blow apart the seattube/top tube junction. Mentally multiply to that 2,3,4g transient loads from potholes etc...You'll see we are dealing with appreciably large forces on relatively thin walled tubing. An inch of post inside the frame with a 200 pound you a foot above is 2400 pounds of bending force. Well over a ton...& that's just a static value. A simple unexpected bump could easily make momentarily well over 10,000 pounds or more lever force trying to pry your bike apart.
Don't be stupid. Get a longer post that at least extends down to below the lower top tube weld.
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06-07-22, 10:12 AM
#32
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Why?
It's a first-order lever.
The seat-post clamp is the fulcrum. Larry is the effort force (200 pounds @ 12 inches distance.) The bottom of the seat post inside the frame is the load (600 pounds @ 4 inches from the fulcrum).
First-order levers are force multipliers.
You might be thinking a second-order?
It's a first-order lever.
The seat-post clamp is the fulcrum. Larry is the effort force (200 pounds @ 12 inches distance.) The bottom of the seat post inside the frame is the load (600 pounds @ 4 inches from the fulcrum).
First-order levers are force multipliers.
You might be thinking a second-order?
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06-07-22, 10:16 AM
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Why?
It's a first-order lever.
The seat-post clamp is the fulcrum. Larry is the effort force (200 pounds @ 12 inches distance.) The bottom of the seat post inside the frame is the load (600 pounds @ 4 inches from the fulcrum).
First-order levers are force multipliers.
You might be thinking a second-order?
It's a first-order lever.
The seat-post clamp is the fulcrum. Larry is the effort force (200 pounds @ 12 inches distance.) The bottom of the seat post inside the frame is the load (600 pounds @ 4 inches from the fulcrum).
First-order levers are force multipliers.
You might be thinking a second-order?
Larry is 260 pounds.
06-07-22, 10:26 AM
#34
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Why?
It's a first-order lever.
The seat-post clamp is the fulcrum. Larry is the effort force (200 pounds @ 12 inches distance.) The bottom of the seat post inside the frame is the load (600 pounds @ 4 inches from the fulcrum).
First-order levers are force multipliers.
You might be thinking a second-order?
It's a first-order lever.
The seat-post clamp is the fulcrum. Larry is the effort force (200 pounds @ 12 inches distance.) The bottom of the seat post inside the frame is the load (600 pounds @ 4 inches from the fulcrum).
First-order levers are force multipliers.
You might be thinking a second-order?
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"Everybody's gotta be somewhere." - Eccles
06-07-22, 10:26 AM
#35
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06-07-22, 10:35 AM
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06-07-22, 10:37 AM
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06-07-22, 10:42 AM
#38
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06-07-22, 10:44 AM
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Ha!
Ok, you both are right!
While diligently working on my BFEngineering degree, I was turning the result in my head of running it as a second order to find the tension the seat/top tube junction was under & not just the load at the bottom of the seat post...I came back to say you may have been on to something. I see you were right about that, too!
Ok. It's time I realize my BFEngineer license is due to be revoked. Where do I turn it in at?
Ok, you both are right!
While diligently working on my BFEngineering degree, I was turning the result in my head of running it as a second order to find the tension the seat/top tube junction was under & not just the load at the bottom of the seat post...I came back to say you may have been on to something. I see you were right about that, too!
Ok. It's time I realize my BFEngineer license is due to be revoked. Where do I turn it in at?
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06-07-22, 10:47 AM
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I've seen a lot of bad ideas suggested on these forums but welding an extension on an alloy seatpost has to be right at the top. I mean we're talking pennies on CL for a proper one.
06-07-22, 10:50 AM
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I think if you are going to talk about maximum seat height, you need to discuss max headroom as well. Very important to this thread.
06-07-22, 10:53 AM
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We keep saying that a proper seatpost is available. However, OP claims he should be riding a 63 cm frame but is on a 47 cm frame. A 350 or 400 mm seatpost might not be big enough. There might not truly be a long enough seatpost available. That doesn't solve the problem that he should be riding a frame that fits though.
06-07-22, 10:59 AM
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I'd be be worried about all of that weight out over the front wheel/axle. That bike might handle like crap, especially when climbing. OP probably thinks he has a brake dragging or a flat tire when going uphill. Come to think about it, didn't he have a thread about his disc rotors rubbing? I can see why.
06-07-22, 11:18 AM
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06-07-22, 11:22 AM
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I'd be be worried about all of that weight out over the front wheel/axle. That bike might handle like crap, especially when climbing. OP probably thinks he has a brake dragging or a flat tire when going uphill. Come to think about it, didn't he have a thread about his disc rotors rubbing? I can see why.
06-07-22, 11:27 AM
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It's a great idea. It gives the user a chance to see firsthand failure modes in compromised alloys subjected to cantilever bending. (But he really should spend his time riding looking between his legs to be sure he doesn't miss the key moment. And with the money he saves on a new post, he can invest in a bridge I'm proposing. Based on the breakthrough Tacoma Narrows design.)
