# How do you calculate the frictional losses in wire ropes over sheaves?

I am currently pulling a load with a wire rope that is moved through a system of sheaves, but had to replace a smaller wire rope cable (1/2") with a larger wire rope cable (3/4"). The sheave/wire diameter ratio is below the recommended guidelines, which I understand affect fatigue life and strength.

However, I have also noticed that the motor seems to work with a lot more effort than it did before, so I wanted to compare the frictional losses of the smaller cable with those of the larger cable to see if the diameter is making the difference.

Is there any formula, perhaps empirically-derived, or a table that could gauge the relative frictional losses between these two systems?

• Do a search, lots of info, this is but one : researchgate.net/publication/… – Solar Mike Nov 17 '18 at 15:28
• There are two points of friction in the cable itself associated with each sheave. Making the bend onto the pulley and straightening out after the pulley. For a given sheave diameter/cable diameter ratio and a given sheave groove/ cable diameter ratio, the friction is pretty constant regardless of the angle of bend around the pulley above a certain minimum bend. The friction is also a function of the cable material and construction. So basically, you work from tables supplied by the manufacturer. Using a cable correctly sized for the groove is very important if memory serves. – Phil Sweet Nov 17 '18 at 20:11
• Memory seems to tell me that the maximum rope diameter is about half the distance between the flanges... – Solar Mike Nov 18 '18 at 5:39
• That article talks about static friction in wire rope around a sheave, but I am trying to figure out frictional losses in a sheave that rotates. Most talk about a constant frictional loss based on the type of bearing, but I would think that wire rope should also figure into the equation: a more rigid wire rope should require more energy to bend at the points Phil mentioned. The tables I have found just suggest a minimum pulley diameter, but the frictional effects don't seem to be quantified. – gsolorzanop Nov 19 '18 at 13:25