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Danger of this frame modification?

Old 03-06-05, 08:10 AM
  #1  
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my friend has a cheapo wallmart bike thing that he wants to mess around with. he's thinking about removing the seat tube and just having the thinner white tubes support the weight. he's also thinking about modifying the fender to support the rear of the bike. but all in all, is this a bad idea for him to be removing that seat tube?? im thinking its a bad idea, but thoughts from people in the know would be appreciated.
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Old 03-06-05, 08:51 AM
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A Darwin Award candidate.
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Old 03-06-05, 08:51 AM
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I'm no engineer, but I suspect the frame will collapse under his weight if he cuts out most of the seat tube (i.e., between the bottom bracket and the top tube). The seat stays just aren't designed to carry that much load.
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Old 03-06-05, 08:53 AM
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this is a joke, right?
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Old 03-06-05, 04:42 PM
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Geez, I wouldn't think a Wal Mart bike would be safe riden as is.
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Old 03-06-05, 04:44 PM
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poor man's suspension??? .....bet it'll be a comfortable ride, but won't last long....
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Old 03-06-05, 04:53 PM
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not even a funny joke!
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Old 03-06-05, 06:51 PM
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The frame is made of not so resilient low carbon steel. It will be weak at best, since the frame is designed to have the seat tube be the load bearing member. With it not there, the trussing of the remaining tubes will kink most likely and at the very least the seat will have no lateral stability. Not a wise idea.
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Old 03-06-05, 08:08 PM
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People have been doing that mod to low-rider bikes for years.

here's an example
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Old 03-06-05, 09:29 PM
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That is in my opinion not an acurate comparison. The bike in your example uses a smaller frame and an axle-supported banana seat. On the beach cruiser sized frame there are much longer runs of tubing for flex to affect.
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Old 03-06-05, 11:39 PM
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Originally Posted by modmon
im thinking its a bad idea, but thoughts from people in the know would be appreciated.
Tell your friend he's an idiot. If he insists on doing it register at the flower shop so all you have to do is call for the "Get Well" or "Sorry for your loss" flower arrangement
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Old 03-06-05, 11:42 PM
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Put pivot points at the top tubes, then remove the seat tube and replace it with a shock...
What is that guy smoking?
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Old 03-06-05, 11:44 PM
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Originally Posted by slvoid
Put pivot points at the top tubes, then remove the seat tube and replace it with a shock...
What is that guy smoking?
Dunno, but I bet a guy could get rich selling it.
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Old 03-07-05, 12:04 AM
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GAARRR! My eyes...
Ignoring the ride quality, why do people even buy bikes that look like that? They're so darn ugly. What's with the curved tubes and loopy white thingies?

I guess I'm a stickler for form-follows-function. I like a pretty bike, but I like to see that every physical feature is there for a purpose too.
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Old 03-07-05, 08:46 AM
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Do it anyway, it will be funny when it breaks. Then post pictures.
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Old 03-07-05, 10:43 AM
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And you people think I'M crazy?
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Old 03-07-05, 11:15 AM
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Originally Posted by CdCf
And you people think I'M crazy?
Hehehe I'm gonna downgrade you to eccentric. This guy is trying to remove major structural elements of his bike. Freakin' nuts.
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Old 03-07-05, 08:27 PM
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Give it a try. Kestrel has been doing it for years and their bikes are hot sellers:https://www.kestrel-usa.com/bikes/airfoil.php

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Old 03-07-05, 08:31 PM
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If he's got balls for coming up with the plan, he probably won't have them after trying it.
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Old 03-07-05, 08:59 PM
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Originally Posted by Sprocket Man
Give it a try. Kestrel has been doing it for years and their bikes are hot sellers:https://www.kestrel-usa.com/bikes/airfoil.php

Well... Cannondale builds a fork with only one blade. Softail makes a bike with neither seat tube nor seat stays. The catch is that they specifically overbuild the other affected components so that they can handle the strain.

I'm not sure that Walmart has designed their bikes for de-seattubification.
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Old 03-07-05, 09:31 PM
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The lefty fork is almost exactly like what aircraft have been using for decades, so that has the least of the worries in my book. The real designs have a set target and they engineered all elements to reach it with a margin. The walmart bikes are made to be just strong enough to not break under normal loads. Name of thier game is low cost. There are few mods I would consider to a walmart, most of the time are bracing, not deleting...
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Old 03-08-05, 12:16 AM
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Originally Posted by CdCf
And you people think I'M crazy?
Yes, and I still do to a point. Here's why: Just as there are varied degrees of mental illness this numbskull is a much more severe case than you are. You do things that are (in my opinion) obsessive, redundant, and impractical. This guy does things that are borderline suicidal and / or will injure him with a great deal of certainty.
CdCf I will say this much at least you have a somewhat understandable reason for some of your ideas. You don't just do things because you think they "look cool"

Originally Posted by mtbikerinpa
The lefty fork is almost exactly like what aircraft have been using for decades, so that has the least of the worries in my book.
I trust Aircraft engineers a lot further than I do the folk at "Crack-n-Fail" but that's me
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Old 03-08-05, 12:58 AM
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Originally Posted by Raiyn
I trust Aircraft engineers a lot further than I do the folk at "Crack-n-Fail" but that's me
Lol.
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Old 03-08-05, 02:00 AM
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He should start making mods on his new wheelchair too!




Originally Posted by modmon
my friend has a cheapo wallmart bike thing that he wants to mess around with. he's thinking about removing the seat tube and just having the thinner white tubes support the weight. he's also thinking about modifying the fender to support the rear of the bike. but all in all, is this a bad idea for him to be removing that seat tube?? im thinking its a bad idea, but thoughts from people in the know would be appreciated.
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Old 03-08-05, 02:11 AM
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Originally Posted by ultra-g
He should start making mods on his new wheelchair too!
Naww I vote for airbrush work on the casket.
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