I want to turn my bike into a motorized one, but i can't get engine clearance because the 2 tubes in the picture are so wide on my bike. I was wondering if I cut those tubes and replace them with thinner tubes will the bike still be safe to ride?

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    If you want a motorbike, buying a second-hand motorbike is almost certainly going to be cheaper than jury-rigging one from a pushbike and an engine. – David Richerby May 12 at 12:11
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    Up-voted because while the OPs plan is not good, the question is good. It is clear, in our scope, and answerable. In other words, it is far better someone asks here than doing something silly. – gschenk May 17 at 15:58


Those tubes are what stop you hitting the ground - hard. If your modification fails you could have a very bad day, or a very bad (even brief) rest of your life. A competent frame builder could modify a frame if it's steel, but would probably find it easier to purpose-build a frame.

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    Frame is most likely aluminum or carbon - steel frames do not benefit significantly being oversized. – mattnz May 12 at 21:56
  • @mattnz I suspected aluminium, which is why the mention of steel is a bit of an afterthought. But a small picture on a phone screen with freehand markup on top doesn't give much away and it's not impossible that someone's using oversize steel gas pipe to build hardtails. – Chris H May 13 at 5:41

Regardless of whether a modified frame would be structurally safe, modifying the frame wold almost certainly more expensive than just buying a different frame more suited to your purpose.



That you have to ask such a question suggests a lack of the engineering skills and experience required to bring such a project to completion, safely.

Also, any engine that won't fit in your bike will likely be too big to be legal on the road of first-world countries.

The existing brakes really won't suit anything larger than a couple hundred watts, which is 1/5 of a horsepower.

If you want an ebike then look for a retrofit kit that puts a hub motor inside your wheel's hub. If you're fixated on a liquid fuel engine, then try the mechanics SE site.

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