Belt Stretch and Stepper Holding Measured

You’ve got a substantially larger extension there for the Gates GT3 I believe, but that’s not suprising given the somewhat improvised nature of my “test equipment”.

What is interesting is that you have a much smaller difference between your Gates GT3 and the regular Fiberglass belt, so either my OEM Fiberglass belts were particularly bungee cord like or my GT3 sample is less stretchy.

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Thank you for taking the time to do the testing!


It seems to me that data shown on the chart differs significantly from that in the table. :confused:


Whilst digging in the Gates belt data I found their spec for the fiberglass cord in their GT3 belts giving (for the 9mm);

  • breaking strength min 190lbs (no, stop, you’ll break the stepper motor)
  • tension for 0.1% elongation 5.7 lbs

Taking The_real_janderson’s measurements of a sample belt; 0.68% for 38lbs this equates to 5.59lbs tension for 0.1% elongation, which is pretty close to the spec (no tolerance given in the spec). Always nice to see consistent data points.


Use the table rather than the chart then?

Yep, I saw that thanks and read the table for the Gates belt sample instead of the chart.