Anyone cut off their top tube?

curtisfox

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Dec 29, 2008
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Very risky, the bike can collapse. The frames forum a triangle and if you remove one it will no longer be and collapse.........Curt
 
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5-7HEAVEN

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Aug 2, 2008
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A fellow member is doing a midframe pocket bike engine build on a BMX.

It's a very tight fit.

However, all the tubes and stays will remain unmolested.

So far, the only welding to the bike will be a triangulated brace from the bottom tube to the motor mount.
 

5-7HEAVEN

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Aug 2, 2008
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It depends where and how the engine is mounted.

Yes, I've seen instances in old board track racers, where the engine block braced two sections of the frame's down tube.

However, the bike's top tube was intact.

FWIW, I ran an electric hub, rear friction drive, and front and rear friction drives on a girlie cruiser.

It had no top tube, but the bottom tube was heavily braced.

When loaded to 6 SLA lead batteries, I could literally FEEL! the bike's frame twisting, ever so slightly.
 

LR Jerry

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Dec 19, 2011
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Very few BMX frames will allow you to do a mid frame mount without frame modifications.
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A rear mount is probably the best option without modifying the frame.
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wolframore

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Nov 10, 2016
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Related but different. I found a girls beach cruiser and cut the top tube and rewelded higher. People love the frame and it’s had no issues over 7 years. My old welds were pretty ugly but strong . The fenders didn’t last. I welded in a tube in the back for rear engine mount
183E32E0-DA6E-455D-86DE-99A7D9235259.jpeg
 

5-7HEAVEN

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Aug 2, 2008
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Well I just picked up a 16" kids bike. I should be able to cut off the top tube now right? The frame is so small
My opinion, that's a "Dead Man's" choice.

Unsafe at any speed.

Even a 20" bike would be squirrelly to handle above jogging speed.
(Ask me how I know that.)

I'd choose at least a 24" bike.
 
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LR Jerry

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Dec 19, 2011
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My opinion, that's a "Dead Man's" choice.

Unsafe at any speed.

Even a 20" bike would be squirrelly to handle above jogging speed.
(Ask me how I know that.)

I'd choose at least a 24" bike.
That's a bike with 24" wheels. A 24" frame would be for a person over 6' tall.