Expert: Paul Klarreich - 1/23/2006

Question
We bought a treadmill about a week ago.  The treadmill has 15 different positions for the incline, but these 15 positions are not according to incline percentages.  For example, when I set it at the 5th incline position, I have no idea what percent incline that is.  Could you help me figure this out?  I imagine I could use trigonometry to figure this out, but I don't remember how to do this (I took trig in the late 1970s).  A giant protractor would come in handy!  Maybe I could do some measurements to figure it out.

Thanks!
David

Answer
Hi, David,
Your Question:  We bought a treadmill about a week ago.

>> and it still works?

The treadmill has 15 different positions for the incline, but these 15 positions are not according to incline percentages. For example, when I set it at the 5th incline position, I have no idea what percent incline that is.

Could you help me figure this out? I imagine I could use trigonometry to figure this out, but I don't remember how to do this (I took trig in the late 1970s). A giant protractor would come in handy! Maybe I could do some measurements to figure it out.

1. Use some chalk to mark the position of the rear roller for the belt, and also to mark the front position.

2. Determine the distance between the two marks, which we will call r, the 'length' of the belt.

3. Set the incline to zero (lowest).  Determine the height of the top of the belt at each of the marks, and confirm that these are the same.

4. Now set the incline to some other level, i.e. raising the front of the belt so you have to walk 'uphill'.

5. Again determine the height of the top of the belt at each of the marks; they should no longer be the same.  Call the difference between the heights h.

6A. The 'percent grade' incline is the ratio h/r as a percent.  For example, if the belt is 50 inches long between the marks and the difference, h, is 2 inches, that is a 2/50 or 4% grade.

6B. The angle of inclination is arcsin(h/r)