Remove top tube of bike and weld lower?

[DeniseNJ]

I have a friend who is too short for her bike.  Even though the top tube is at an angle, she has a hard time with it.  So I sawed it off to weld it back on lower.  Bad idea:  Top tube is now too short of course, so I'm buying a new aluminum tube.  It's aluminum, which can't be welded with my machine.  I could braze it with a torch but I might set the entire bike on fire since the bike is not exactly in pieces.  I can't take it entirely apart since I'll never be able to put together.  The list goes on.

My question is will affixing the top tube lower on the seat pole destroy the geometry of the bike and make it fall apart?  I'm going to use an epoxy, JB Weld (?) to affix, sand down, spray paint.  My own bike is a step through but it weighs a ton and I'm sure is steel.  Will the absence of triangles destabalize this bike to the point of being dangerous?  She's just a recreational rider.  Do I owe my fiend a new bike?

I tried to encourage her to sell it and buy one that fits.  She bought at a bike shop so not sure why they sold this to her in the birst place.  It was a 500 bike on sale for 300 so she bought it.  She didn't want to spend any more money or get a crummy bike so she asked me to fix hers.  I didn't relaize what I was getting myself into. 

[ncornilsen]

Dude, throw the bike in the trash and get her a new one. You'll all be money ahead.

Bikes use incredibly thin, custom alloys for their frames. The welds and members are all highly stressed. Home-brewing a frame like this is extremely risky and unlikely to work very long... JB weld etc will not hold up very long. Cutting the bar you did eliminated the frame's triangulation.

When the frame breaks and she goes to the hospital for the likely injury, $500 will look cheap for the right bike.

-Nick

[kendallf]

My question is will affixing the top tube lower on the seat pole destroy the geometry of the bike and make it fall apart?  I'm going to use an epoxy, JB Weld (?) to affix, sand down, spray paint.  My own bike is a step through but it weighs a ton and I'm sure is steel.  Will the absence of triangles destabalize this bike to the point of being dangerous?  She's just a recreational rider.  Do I owe my fiend a new bike?

I concur with ncornilsen, I'd throw it away personally.  If you are determined to fix it, you need someone who can TIG weld aluminum well, you need to get a decent frame quality alloy aluminum tube, and you need to accurately notch it for the fit to the head tube and to the seat tube.  The geometry of the bike won't change as long as you didn't bend it while cutting the tube out.  Here's the only source I know of who sell aluminum frame tubes to the public. 

https://www.cycle-frames.com/bicycle-frame-tubing/TUBES-ALUMINUM/

FWIW, I am an experienced TIG welder, I bought a frame jig, and I threw away the first steel frame I started on after I wasn't happy with the weld quality.  It's definitely a craft.  We have a custom framebuilder who's a frequent poster on this forum but I'm guessing he'll stay away from opining on this.. lol.

[nereo]

I'm all for DIYing, but I gotta side with ncornilsen here - you've permanently compromised the structural integrity of the bike frame and you are never going to get that back with the methods you describe. It's now dangerous for anyone to ride, and there's no reset button.  The frame is done, toast, finished, dead, kaput.

Yes, you owe your friend a new bike... or at hte least a new bike frame.

More to the point, if your friend is too short for her bike, she needs a better fitting bike

[lthenderson]

Yes, JB weld is not adequate for what you want to do.  As someone who has also done some TIG welding, which is what you need to do to properly repair this bike, it is not something that you can just borrow a TIG welder and do. It requires a lot of practice and skill to make TIG welds functional and look nice.  To me, the only option is to buy your friend a new bike.

[DeniseNJ]

I'm all for DIYing, but I gotta side with ncornilsen here - you've permanently compromised the structural integrity of the bike frame and you are never going to get that back with the methods you describe. It's now dangerous for anyone to ride, and there's no reset button.  The frame is done, toast, finished, dead, kaput.

Yes, you owe your friend a new bike... or at hte least a new bike frame.

More to the point, if your friend is too short for her bike, she needs a better fitting bike

Oh, good grief.  It was her idea.  My flux core welds are super strong but of course did nothing for this.  Even trying to braze worked on a scrap piece of aluminum but did nothing for the bike pole.  So where to I get a new frame, since she is just too short for this one?  (Dang it--I should have just kept the bike myself and bought her a new one.  I think it's a trek)

What about this: https://newjersey.craigslist.org/bik/d/livingston-trek-72fx-hybrid-bike-for/6904792041.html
I have to see exactly what she has.  Ugh.

[roomtempmayo]

Like others have said, the frame is toast. 

The Trek you link to above is a nice town bike.  Swap the rear wheel from the other frame (you may need to also swap cassettes, which requires a cassette tool, a chain whip, and a big hex wrench), and she should have a nice bike if it fits her.

[DeniseNJ]

Like others have said, the frame is toast. 

The Trek you link to above is a nice town bike.  Swap the rear wheel from the other frame (you may need to also swap cassettes, which requires a cassette tool, a chain whip, and a big hex wrench), and she should have a nice bike if it fits her.

Is this english?  How does someone who knows nothing at all about bikes start taking apart someone $500 bike.  I don't know what on earth I was thinking.  If I can get the onw linked I will swap out the tire, or take it to a bike shop and ask them to make the change.  Maybe I could sell the toasted one for parts.

[nereo]

Like others have said, the frame is toast. 

The Trek you link to above is a nice town bike.  Swap the rear wheel from the other frame (you may need to also swap cassettes, which requires a cassette tool, a chain whip, and a big hex wrench), and she should have a nice bike if it fits her.

Is this english?  How does someone who knows nothing at all about bikes start taking apart someone $500 bike.  I don't know what on earth I was thinking.  If I can get the onw linked I will swap out the tire, or take it to a bike shop and ask them to make the change.  Maybe I could sell the toasted one for parts.

Hey, don't beat yourself up too bad.  We learn from our mistakes, and as someone who's gotten into similar situations in the past you'll look back at this and laugh. For reasons that make no sense now, I once thought it would be a good idea to try to re-spoke a bike rim with nothing more than a multi-tool.  That didn't go well (destroyed the rim, had to start over).

It sounds like you are just learning about bicycles and their components, so if you can I'd find a bike co-op that will allow you to work on this bike while someone with more experience is nearby.  If you a local college nearby, chances are they have a bike co-op.  Next up would be a independent bike shop, hopefully was heavily tattooed mechanics.  Throw yourself at their mercy and the good ones will take pity and show you a thing or too (provided they aren't too busy). Just dont' take it to some big sports store that sells everything from hiking gear to soccer cleats; those places rarely employ bike mechanics that are up the task of rebuilding an entire bike from teh frame up.

As for bike frames, understand that they are actually very well designed components that very carefully balance low weight with high strength.  Most riders won't even trust a frame that's been in a crash and has a small dent, because just a seemingly minor dent can lead to the frame buckling at the most inopertune time (high speed, tight turn) causing a very serious crash.

[BudgetSlasher]

I'm all for DIYing, but I gotta side with ncornilsen here - you've permanently compromised the structural integrity of the bike frame and you are never going to get that back with the methods you describe. It's now dangerous for anyone to ride, and there's no reset button.  The frame is done, toast, finished, dead, kaput.

Yes, you owe your friend a new bike... or at hte least a new bike frame.

More to the point, if your friend is too short for her bike, she needs a better fitting bike

Oh, good grief.  It was her idea.  My flux core welds are super strong but of course did nothing for this.  Even trying to braze worked on a scrap piece of aluminum but did nothing for the bike pole.  So where to I get a new frame, since she is just too short for this one? (Dang it--I should have just kept the bike myself and bought her a new one.  I think it's a trek)

What about this: https://newjersey.craigslist.org/bik/d/livingston-trek-72fx-hybrid-bike-for/6904792041.html
I have to see exactly what she has.  Ugh.

They make different size frames for different size people a quick google of how to size a bike frame will give plenty of results. Here is one from the first page of my search: https://averagejoecyclist.com/bike-frame-size-guide-2/

It sounds like she started out with a frame for someone who was taller (or at least had a longer inseam).

And I echo what everyone else has said, the modification you are attempting to make, even if welded properly, could significantly compromise the bike. If you have no experience with the welding type that is needed this is not the first project and epoxy (at least the kinds you pick up at the hardware store) are not the answer.

[DeniseNJ]

I'm all for DIYing, but I gotta side with ncornilsen here - you've permanently compromised the structural integrity of the bike frame and you are never going to get that back with the methods you describe. It's now dangerous for anyone to ride, and there's no reset button.  The frame is done, toast, finished, dead, kaput.

Yes, you owe your friend a new bike... or at hte least a new bike frame.

More to the point, if your friend is too short for her bike, she needs a better fitting bike

Oh, good grief.  It was her idea.  My flux core welds are super strong but of course did nothing for this.  Even trying to braze worked on a scrap piece of aluminum but did nothing for the bike pole.  So where to I get a new frame, since she is just too short for this one? (Dang it--I should have just kept the bike myself and bought her a new one.  I think it's a trek)

What about this: https://newjersey.craigslist.org/bik/d/livingston-trek-72fx-hybrid-bike-for/6904792041.html
I have to see exactly what she has.  Ugh.

They make different size frames for different size people a quick google of how to size a bike frame will give plenty of results. Here is one from the first page of my search: https://averagejoecyclist.com/bike-frame-size-guide-2/

It sounds like she started out with a frame for someone who was taller (or at least had a longer inseam).

And I echo what everyone else has said, the modification you are attempting to make, even if welded properly, could significantly compromise the bike. If you have no experience with the welding type that is needed this is not the first project and epoxy (at least the kinds you pick up at the hardware store) are not the answer.

Can you use a different size frame with the same bike?  Like she has a Trek 7.2 fx, like in the link a few posts up, but I fould this smaller bike.
 https://newjersey.craigslist.org/bik/d/ho-ho-kus-trek-700-series-15-frame/6895458093.html
 If I remove the frame and clean up nice or even spray paint, can I have a bike shop just switch out the frame?  (I should've done that and not even tell her--then she'd think I fixed her bike and I'm awesome.  lol)  I ordered my bike in the mail and put it together.  Wondering how hard it would be to put together, just switching out the frame and leaving everything else as is--taking it to a shop though so they could check it out.

[lthenderson]

So where to I get a new frame, since she is just too short for this one?

My dad fixes bikes as a hobby. He buys all his frames mostly on eBay. He likes that because you can get a nice frame that is perfect in size and then put on all the components.

[DeniseNJ]

So where to I get a new frame, since she is just too short for this one?

My dad fixes bikes as a hobby. He buys all his frames mostly on eBay. He likes that because you can get a nice frame that is perfect in size and then put on all the components.

So if she say has a 17 inch bike right now and I buy the exact same bike but with a 15 inch frame, can I switch out the frame?  Would all the stuff "fit"?  I would take it to a shop for a proper tune up to be sure it doesn't fall apart under her but wondering bc I found the exact same bike with a 15 inch frame for 100 bucks on craigslist.

[BudgetSlasher]

So where to I get a new frame, since she is just too short for this one?

My dad fixes bikes as a hobby. He buys all his frames mostly on eBay. He likes that because you can get a nice frame that is perfect in size and then put on all the components.

So if she say has a 17 inch bike right now and I buy the exact same bike but with a 15 inch frame, can I switch out the frame?  Would all the stuff "fit"?  I would take it to a shop for a proper tune up to be sure it doesn't fall apart under her but wondering bc I found the exact same bike with a 15 inch frame for 100 bucks on craigslist.

I would make sure that you actually need to switch everything from the current bike to the CL bike; if they are the same bike (only different sizes) its likely they have similar components. If it is in good shape and your friend didn't have a lot of upgrades on their bike swapping over identical or very similar parts could very well be a waste of time and money.

[GuitarStv]

Yikes.

Modifying a frame is a very tricky thing to do.  Kudos for trying, but I have to agree with everyone . . . you're in need of a new frame now.

Yes, the majority of components from the bike should be interchangable.  Most wheels and tires are standardized (700C for road/hybrid bikes, 26" for mountain bikes).  Check that the new frame uses the same size rim and you're all good there.  If it has Shimano 8 speed shifters, they'll play well with most 8 speed cassettes you run across.  The saddle can be swapped over.  The bikes both likely have square taper bottom brackets, so you can swap the cranks over.  The pedals should be easily swappable too (just be careful about the thread direction . . . it's different for left and right).

The brakes are the area most likely to give you difficulty.  The bike you linked has cantilever brakes.  Most newer bikes will have V-brakes.  The levers have a different amount of pull for V-brakes than cantilever brakes and can't be used interchangeably.

[DeniseNJ]

Bought exact same bike in black for $115 that had missing spokes on the back wheel so I switched out the wheels and the seat and now it's the exact same bike in black, which is still too big for her.  But I figured she's back where she started and can sell the bike or not as she wants.  (the very first thing I told her was to sell her bike and use the money to buy a new one but she said she didn't want to spend any money on it.)

Well she decides she wants a new bike and orders one online for $250.  She says she doesn't need any money from me but of course I feel aweful.  So I said I would sell the bike and give her whatever I could get for it and could also sell the parts from the original bike.  ugh.  Now I have THREE bikes in my garage.  She said I should keep hers and sell mine but I like my bike.  So I took the broken one apart to sell the parts and I will sell the new one I "built" but brother what a hassle.

So while taking the old bike apart I remember that you can remove the cassette so I take out the innerds of the back wheel with the broken spoke to remove the cassette.  Well all these greasy little silver balls start falling out of the hole and the more I try to shove them back in the more fell out until I had a dozen of them rolling around my garage! So that didn't work.  All the rest of the parts I took off very carefully, wiped them down, and put aside and will take what I can get for them.  Hoping to build fun stuff with the wheel parts like the inner tubey thing that the spokes are attached to. 

Oh, and she wants me to put together her bike when she gets it in the mail.  She says an 11 yr old can do it.  I used to think we were Lucy and Ethel.  Now it's more like we're Laurel and Hardy.

[GuitarStv]

Before you touch another bicycle, please carefully read through both of these websites:
https://www.sheldonbrown.com/
https://www.parktool.com/blog/repair-help

Working on bikes isn't rocket science, but I feel like you need a bit of a grounding in information before you do anything else that will cost you money.

[DeniseNJ]

Before you touch another bicycle, please carefully read through both of these websites:
https://www.sheldonbrown.com/
https://www.parktool.com/blog/repair-help

Working on bikes isn't rocket science, but I feel like you need a bit of a grounding in information before you do anything else that will cost you money.

LOL--thanks.  I definitely will.  I'm just selling the parts and selling the new bike for whatever I can get for it and walking away.  But I do find bikes interesting and will build what my firend gets in the mail.  Actually, I may even try the bike I just bought for her.  Her's is a trek.  Mine is a purple heavy walk trhough bike I bought on Amazon for $125.  From what I hear and read, big box store bikes are a whole different animal than a "real" bike.  the trek seems to have cool levers and stuff to remove and adjust stuff whereas my Schwin needs wrenches and stuff to move or adjust anything.  And it must weigh a ton.

Thanks for the links, I will definitley give a thorough read.

[nereo]

Before you touch another bicycle, please carefully read through both of these websites:
https://www.sheldonbrown.com/
https://www.parktool.com/blog/repair-help

Working on bikes isn't rocket science, but I feel like you need a bit of a grounding in information before you do anything else that will cost you money.

LOL--thanks.  I definitely will.  I'm just selling the parts and selling the new bike for whatever I can get for it and walking away.  But I do find bikes interesting and will build what my firend gets in the mail.  Actually, I may even try the bike I just bought for her.  Her's is a trek.  Mine is a purple heavy walk trhough bike I bought on Amazon for $125.  From what I hear and read, big box store bikes are a whole different animal than a "real" bike.  the trek seems to have cool levers and stuff to remove and adjust stuff whereas my Schwin needs wrenches and stuff to move or adjust anything.  And it must weigh a ton.

Thanks for the links, I will definitley give a thorough read.

Yes, beware of 'Bicycle Shaped Objects (BSOs)' sold through many big-box stores.  Many feature parts which literally cannot be serviced, and take short cuts to sell them at the lowest possible price-point.
https://www.southcoastbikes.co.uk/Dont-Buy-a-Cheap-Bike

[Car Jack]

Stop.

Admit to yourself that you are not a successful do it yourselfer.  Take her to a bike store.  Have them set her up with a properly sized bike.  Buy that.

Now take the bike you wrecked and put it on Craigslist for $100.

[DeniseNJ]

Stop.

Admit to yourself that you are not a successful do it yourselfer.  Take her to a bike store.  Have them set her up with a properly sized bike.  Buy that.

Now take the bike you wrecked and put it on Craigslist for $100.

I bought the exact same bike on craigslist for $115 with a bad wheel, switched out for her wheels and her seat, and gave that to her.  Fits even better than the original.  I also striped all the parts from her original bike to sell on CL but I'd rather just give them away to anyone who wants them.

[BudgetSlasher]

Stop.

Admit to yourself that you are not a successful do it yourselfer.  Take her to a bike store.  Have them set her up with a properly sized bike.  Buy that.

Now take the bike you wrecked and put it on Craigslist for $100.

I agree that the project that prompted this post was outside of TS's seeming skill set long before they hit "Post", that blanket statement seems a little harsh.

[big_owl]

This was probably one of my favorite threads I've ever read on any forum in the history of the internet.. As soon as I saw JB Weld and bicycle frame I knew that it was (TM) Very Serious.

[DeniseNJ]

This was probably one of my favorite threads I've ever read on any forum in the history of the internet.. As soon as I saw JB Weld and bicycle frame I knew that it was (TM) Very Serious.

Lol.  Glad I could entertain. I've told this story at work to much enjoyment, especially when I describe your responses!

[BudgetSlasher]

This was probably one of my favorite threads I've ever read on any forum in the history of the internet.. As soon as I saw JB Weld and bicycle frame I knew that it was (TM) Very Serious.

Lol.  Glad I could entertain. I've told this story at work to much enjoyment, especially when I describe your responses!

I admire your sense of humor and the relationship you have with your co-workers.

I probably would have asked for assistance behind an anonymous screen name and then done my best to pretend it never happened (of course after making everything right)

[Goldielocks]

This was probably one of my favorite threads I've ever read on any forum in the history of the internet.. As soon as I saw JB Weld and bicycle frame I knew that it was (TM) Very Serious.

Lol.  Glad I could entertain. I've told this story at work to much enjoyment, especially when I describe your responses!

Well all these greasy little silver balls start falling out of the hole and the more I try to shove them back in the more fell out until I had a dozen of them rolling around my garage! So that didn't work.

Dude,  I haven't laughed so hard at a post in a long time.   I think we have all been at this place with the little ball [bearings] falling out while we try to catch them....and shove them back in after 25 minutes of searching...and realize we are still 8 balls short.... maybe not with a bike part, but with SOMETHING....  mine was a pair of drawer glides.