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Replacing a top tube?

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Replacing a top tube?

Old 12-28-21, 03:03 PM
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kawaray
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Replacing a top tube?

I got a custom-built steel frame that is ~10 years old. I decided to get new paint for it this winter, so I stripped it off of components and drop it off with a builder (a different builder from the one had originally made it for me, since I moved to a different state). Upon inspection against a straight edge, the builder noticed about a slight bend on the top tube. The builder does not seem too concerned about the bend, but the problem is that I know it exists! So, I am debating if I should get the top tube replaced. I would like to keep the frame for another good number of years, so it could be worth the investment (and I don't have to keep thinking about the bend when I ride it).

Are there any concerns about replacing a top tube? I am not sure if the tubing material can be exactly the same as the original when it is replaced. I am not too concerned about the weight change, but I just don't know what impacts replacing a top tube has on bike...
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Old 12-28-21, 03:13 PM
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How much of a bend? Do you need a straight edge to see it? Has the bend on the top tube affected the Rake and front fork angle?
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Old 12-28-21, 03:19 PM
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It is very slight, and I did not notice it at all until the builder pointed out. He says the is bent down at the middle, and it does not sound like it is affecting the fork angle or the rake.
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Old 12-28-21, 03:42 PM
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Steve B.
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Leave it alone. It's a design feature these days, curved top tubes.

I mean really, you will be sending back to the builder, if it's a lugged frame they can take it apart and install a new tube, then re-braze, then paint. Tha's pretty expensive, might as well get a new frame. How's it ride, which is really all that matters ?. If it rides fine, leave it alone.
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Old 12-28-21, 03:55 PM
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The chance of doing more damage than any correction is way too high! The risk reward of replacing the top tube is not worth it in my opinion. Let's review some facts. Most frame tubes come to us builders with some kind of bow. It is unusual if they are perfectly straight. Take a good straight edge and go around and check frames and you will see. It is standard procedure for good builders to roll a tube on their alignment table so they can put the bow in the plane of the frame. I bet that is where the bow is on your frame.

The heat required to take a top tube out will stress the frame. There is going to be a debate among builders how much this matters but I wouldn't do it unless the top is truly damaged. Another problem is that it is hard to clean out the sliver residue inside the lugs. I have a powerful sandblaster and that helps but typically a builder can't get it all out and that messes with the miters fitting perfectly against the seat and head tubes anymore.

It isn't about the weight but top tubes come with different wall thicknesses. How thin the tube is affects its ride quality. I would never under any circumstances put a slightly heavier tube in a frame i made myself. This is another area builders might argue. Maybe I'm the kind that can feel a pea under my mattress. Also top tubes varies in butt lengths and a builder can vary where he decides to put the miters compared to the butts. I consider all these factors when building a custom frame. I would not under any circumstances want my name put on a frame I made if another builder replaced a top tube. I would have no idea if he was as careful as I am and as a result take away some quality out of the frame. YMMV. There is a lot of differences in build quality between builders.

If you like the way the frame rides, the chances of reducing the ride quality by replacing a top tube exists. You might think it is worth it but I can guarantee you I would never do it even on a frame I made myself in the beginning.
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Old 12-28-21, 04:12 PM
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Originally Posted by Doug Fattic View Post
The chance of doing more damage than any correction is way too high! The risk reward of replacing the top tube is not worth it in my opinion. Let's review some facts. Most frame tubes come to us builders with some kind of bow. It is unusual if they are perfectly straight. Take a good straight edge and go around and check frames and you will see. It is standard procedure for good builders to roll a tube on their alignment table so they can put the bow in the plane of the frame. I bet that is where the bow is on your frame.

The heat required to take a top tube out will stress the frame. There is going to be a debate among builders how much this matters but I wouldn't do it unless the top is truly damaged. Another problem is that it is hard to clean out the sliver residue inside the lugs. I have a powerful sandblaster and that helps but typically a builder can't get it all out and that messes with the miters fitting perfectly against the seat and head tubes anymore.

It isn't about the weight but top tubes come with different wall thicknesses. How thin the tube is affects its ride quality. I would never under any circumstances put a slightly heavier tube in a frame i made myself. This is another area builders might argue. Maybe I'm the kind that can feel a pea under my mattress. Also top tubes varies in butt lengths and a builder can vary where he decides to put the miters compared to the butts. I consider all these factors when building a custom frame. I would not under any circumstances want my name put on a frame I made if another builder replaced a top tube. I would have no idea if he was as careful as I am and as a result take away some quality out of the frame. YMMV. There is a lot of differences in build quality between builders.

If you like the way the frame rides, the chances of reducing the ride quality by replacing a top tube exists. You might think it is worth it but I can guarantee you I would never do it even on a frame I made myself in the beginning.

Thanks for your response. The bend is in the plane of the frame, so it might have been there from the beginning like you mention? I was not fully aware of the process involved in replacing the tube, so I am now getting convinced that it may not be worth the hassle.
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Old 12-28-21, 06:14 PM
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Another vote for leaving it be. Just curious, did your builder mention how much the offset was?
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Old 12-28-21, 07:13 PM
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I didn't get the value for the offset. He just mentioned that it was very slight when checked against a straight edge.
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Old 12-28-21, 08:19 PM
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It's not so much the offset but where it's centered and if there's any other frame integrity issues. Bowed tubes (which this sounds like) are not uncommon. If the tube has a gradual bow then it's less a concern. But a focused and localized one (front end impact ripples, as example) are another thing. Andy
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