BMX Specs: Trimoly

Trimoly is a term often seen on mid-level BMX bikes. Bmx companies use this term to describe a frame that has a mix of strong chromoly and weak hi-tensile tubing constructing the frame. While it is better than a plain hi-ten frame, don't be fooled by the weak aspects.

showing what trimoly is

What is Trimoly?

Trimoly is (Triangle and Chromoly) mixed together to make a word. This sounds a lot better than some chromoly and some hi-tensile steel. When you see that a bike has a trimoly frame, imagine the top tube, head tube and downtube are strong chromoly. While the chain stays and sometimes seat tube are weak hi-tensile steel.

Read about the difference in hi-tensile vs. chromoly here.

Why is it important?

Here's why I care, I was suckered into getting a trimoly frame once. It was a pretty light killabee killarado frame. I thought it was chromoly, and therefore stronger. But after a few months of 360s and 540 attempts, I noticed that the back end had bent from constant contact.

A beginner to mid-level rider might not care too much. For riders with a bigger bag of tricks, it might be a good idea to get a full chromoly frame.


  • Back end will bend with continued spins
  • The welds are weaker due to the different metals being used
  • Will be a little heavier than chromoly frames

Does it really matter?

Just make sure you understand what level of riding you do. For a beginner, this is a stronger frame than the other options. But for a seasoned rider, you will shred through this frame. No one wants to replace a frame every few months.

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