Cutting Carbon the right and the wrong way.


The Performance Bike Scoop happens every Wednesday at 3:00PM EST on our Performance Bicycle Facebook page.

This week we had the opportunity to test the durability of carbon fiber on a discarded frame damaged in shipping. This was a great opportunity for us to demonstrate how strong carbon fiber really is and the best practices for cutting carbon handlebars and steerer tubes.

Check out the video below.  We’ll admit, we had some fun during this one.

If you’re thinking you need some carbon cut out of your life, we’re more than happy to help!  If you live close to one of our shops then please swing through anytime.

The two most common carbon components you might want to cut will be steer tubes and mountain bike handlebars.  In some instances there could be a need to cut a seat post, and on the rare occasion, some seat tubes and masts need to be cut.  The process is pretty much identical for all of them.

Things you do not need to cut are pretty obvious.  These would be things such as parts of the frame, road specific handlebars, stems, wheelsets, saddle rails, etc.

If you’re looking to do it yourself, here are some must have tips and tools you’ll need before beginning the process:

  1. A good understanding of bicycle fit.  Cutting steer tubes, mountain handlebars, and seat posts all are to achieve the best bike fit.  Some folks need more upright positions, lower saddles, wider or shorter handlebars, etc.
  2. Adoption of the rule that you need to measure 5X and cut 4X.  Once you cut it off you can’t put it back on . If you go too short you’ll have to buy a new one, and carbon isn’t all that cheap.
  3. Tape to wrap around the component you’re about to cut.  Wrapping it in a couple layers of tape helps prevent the carbon layers from splintering when you take the hacksaw to it.
  4. Speaking of hacksaws, you’ll need one of those too!  The blade is the most important part.   Most hacksaws come with around a 24-25 tpi (teeth per inch) blade.  That’ll do the trick just fine, but having a finer blade that’s around the 30 tpi mark will help you make a better, smoother cut.
  5. A sharpie.  When you’re measuring those five times, you’ll want to use the sharpie to mark the spot you’re going to cut.  No eyeballing it!
  6. A tube cutting guide.  Slide the component into the guide and when the sharpie mark lines up, clamp it down just to the point where it doesn’t move.  Over tightening could damage the component!
  7. A vice securely attached to a bench, or other similar surface.  Putting the tube cutting guide into the vice helps secure everything in place, gives you the stability you need to make a good cut, and prevents you from hurting yourself!
  8. Sandpaper.  After you make your cut, take off the tape and use some sand paper to smooth out the edges.
  9. A torque wrench.  You’re going to need to put those components back on your bike so you can ride it, but be sure to use a torque wrench so you don’t over tighten the bolt and crack the frame or the component you just cut.  Most carbon is recommended to be torqued to around 5nm, but make sure to read the manufacturer’s suggested spec, as a lot of them are slightly different.

If in the unfortunate event you get in a crash and break a carbon component you should always replace it.  If you suspect your carbon frame is damaged in an accident, take it to your local shop to have it inspected.  There are carbon repair companies out there who are highly talented and can fix your carbon bike!  Doing these repairs will void your manufacturer warranty, but most repair companies will give you a warranty on their work.  At the end of that day that’s a pretty great option.

If however your frame is damaged and not repairable you will need to dispose of the frame properly.  One fun way to get rid of it is to hang it in your shop or turn it into a piece of art (a pretty expensive piece of art!), but whatever you do, make sure the frame is clearly marked as broken and unrideable, or the frame is broken in half so it’s obvious it’s damaged, like we demonstrated in our video.

Thanks for reading and watching, and check out the Performance Bike Scoop every Wednesday at 3:00PM EST on our Facebook Page.

~Bike Scoop

One thought on “Cutting Carbon the right and the wrong way.

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