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I want to cut the crossbar on a mens bike to make it easier to get on and off. Will it damage the bike?

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    What do you mean by "crossbar"? Are you talking about the top tube (en.wikipedia.org/wiki/Bicycle_frame#Top_tube)? – sleske Sep 16 '15 at 16:09
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    If you mean the top tube in a classical "diamond" frame. No. You will destroy the integrity of the bike. You should trade the bike for one with a "mixte" or "woman's" frame. – Daniel R Hicks Sep 16 '15 at 16:10
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    If the top tube wasn't important it wouldn't be there in the first place. – whatsisname Sep 16 '15 at 17:00
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    Don't cut it - you'll destroy its strength. If you want a stepthrough then buy one off bay or craigslist or go to the local bike cooperative and swap. At ours, ladies bikes are less popular so we've got stacks of them. – Criggie Sep 16 '15 at 21:44
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    All the other comments are far too serious. Can you cut it? Yes, certainly! Will the bike (or you) survive if you ride it afterwards? Probably not. Would it be fun to watch? Depends if you like American humor – andy256 Sep 17 '15 at 7:12
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This is downright dangerous and should never be done on a bicycle someone intends to ride. The top tube is integral to the strength of the bike. The frame can buckle or worse when you try to ride it.

First, make sure you're looking at the right size of frame. If its too big, it's going to be hard to get on and off from. You can buy a stepthrough frame or a mixte frame if you want something easier to get off and on, or a recumbent bike.

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Yes it will damage the bike. Frames that have that top tube rely on that bar for structural integrity. Other bikes with step through frames are built to add rigidity elsewhere.

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    But they are never as rigid as a diamond frame. – andy256 Sep 17 '15 at 7:14
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    Mixtes can be as rigid as diamond frames. – Batman Sep 17 '15 at 13:29
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    For a given weight and construction technique, a diamond frame will always be more rigid than any other frame shape. – LeoR Sep 17 '15 at 13:48
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When you sit on a bike with a traditional diamond frame, your weight on the saddle pushes the bike down and this force is resisted by the wheels where they contact the road. The tendency of the bike to "sag" in the middle under your weight is resisted by the top tube – without it the seat and handlebars would be forced towards each other by the reaction of the wheels to your weight. I'm not sure if an adult could even sit on a bike with the top tube removed, there would be a large bending load on the downtube.

Frames that are built without a traditional top tube (for example mixte and step-through frames) use other means to resist this tendency and are not (generally speaking) able to be as strong or as light as the diamond frame. One of the very wonderful things about bicycles is the elegance of design that goes into creating light, strong structures. Every bit has a purpose.

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    Yeah, the diamond frame (double triangle) is a very strong design that minimizes weight while still remaining relatively strong for an affordable price. It's similar to the way many bridges are constructed. You can find alternative bike designs, but they generally made for very specific uses such as when things like aerodynamics is more important than weight, price, or strength. – Kibbee Sep 17 '15 at 12:42
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    "Every bit has a purpose." Some people would argue that the freewheel and rear brake are superfluous. (wink) – RoboKaren Sep 17 '15 at 19:03
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Nope! The force on the down tube/seat tube connection would be too strong. You'd break the frame right there and crash horribly.

  • Not necessarily (immediately). I've had diamond frames fail me, and each time it was the fact that there was a second tube that saved my ass. However, it was always the lower tube that broke while the upper tube remained intact. Your bike suddenly gets very springy when that happens, which should be the cue to get off the bike immediately. Because the next pothole, root, branch, whatever can kill the remaining tube. (Btw. that's the reason why I would never trust a Y-frame: There's simply no backup if anything breaks. I've learned to avoid single points of failure...) – cmaster Mar 27 at 22:39
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I've often wondered this myself. There is a manufacturer that eliminated the downtube and replaced it with a cable.

I have broken the seat tube on a frame and ridden it home that way. It was more flexy, but it was rideable.

When you ask these kinds of questions, you get an immediate kind of response exactly as you see above, usually with no empirical basis.

Based on what it felt like to ride a bike with broken seat tube, I think you'd find WAY more flex, and as the frame flexed, your seat tube and headtube angles would change. I believe you'd notice that in the way the bike handles. Would the frame eventually fail? It probably depends on the frame. If you have a chunky steel frame, it might just flex and steer differently, but hold up indefinitely.

If it's a steel bike you can afford to lose, my advice would be to try it and see. Steel fails in a slow predictable way. You'll see if it bends past its ability to recover or start to crack. Take it on an easy ride first, somewhere flat.

  • Do you have a reference for the cable downtube bike? It sounds interesting – I'd have thought that there would be some compression loading on the downtube at least some of the time – and I didn't have any luck searching for it. – dlu Sep 18 '15 at 0:52
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    @dlu the cable bike Lee mentioned was a Slingshot. – Klaster_1 Sep 18 '15 at 2:19
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    The Slingshot folder seems like a cool idea. The depth of the top tube make me think that they are taking the compression loads there and the purpose of the wire is to hold the top tube down. – dlu Sep 18 '15 at 3:23
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    "You get an immediate kind of response" because people are trying to prevent others from getting killed. The safest approach to a question like this is to assume the person asking is not familiar with the risk involved, and thus the community answers with "doing that is dangerous, beware". The opposite may lead to someone trying this absentmindedly getting themselves in a situation that can be fatal. – LopSae Sep 22 '15 at 21:39
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    While an Interesting response, this doesn't address OP's question which was about removing the top tube, not the downtube, which experiences more compression loads not tension loads, so your answer really doesn't apply to this question. Leaving for completeness. – Criggie Mar 24 at 5:50

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