# Trying to determine actual load (PSI) on a drive chain

1. May 25, 2012

### maximiliano

I think I have a rough idea how to get there.....but I'm not sure.

Let's assume I'm riding a bicycle, and I'm peddling at a constant pressure (torque). This is a peddling pressure which would be the exact amount which would just lift a 50 pound weight off the ground and hold it there.

Okay...so as I'm peddling along, with precisely this much pressure on the chain.....can I assume that is the EXACT pressure (in pounds) that each link of the chain is experiencing? IF SO, if I then calculate the surface area of each link that is exposed to peddling pressure to be 1/20" on one side of the pin and 1/20" on the other side, thus a total load bearing area of .1".......would I just then multiply the 50 pounds of total pressure by 10 (1 / .1)....for a total pounds per square inch being loaded on each link to be 500 psi??

Or.....am I all wet on this calculation? What I'm attempting to do is to describe to some people how much actual pressure, in psi, each chain link is loaded by when someone is climbing a mountain at a constant speed. I used the 50 pounds of pressure as a guestimate of the torque required to do this. It's in that ballpark, but that number is not as important as it is to be able to calculate the PSI per link once the overall torque is known.

Thanks!!

2. May 26, 2012

### Pkruse

Maybe not wet, but at least damp.

Pounds is not a torque unit.

If you put 50 pounds of force on the crank, then the maximum force on the chain will be bigger than that by the ratio of the radii of the crank and the front chain ring. The part of the chain that sees this force is the length on top between the chain ring and the cluster. The rest of the chain essentially sees zero load, except that produced by the tensioning device in the rear derailleur.

I have no idea what you are looking for in psi. If you are looking for the maximum stress in the chain, then figure the smallest cross sectional area of the steel in the chain. Divide the chain load figured above by that area. If you are looking for contact pressure between the chain and the sprockets, which will be highly variable as a function of many factors that get more complicated that we probably need to talk about here. But rest assured that contact pressure is very small.

3. May 26, 2012

### huntoon

I agree with Pkruse, with the exception that if you are mountain biking, you probably are strapped or clipped in. This could double the force (push and pull) that you exert on the pedals.

FYI:

Force is in Pounds (lbf) or Newtons (N)
Torque is in foot*pounds or inch*pounds or Newton*meters
Pressure is in Pounds per square inch or Newtons per square meter.

Another factor to consider is slip. You can only transmit as much force to the chain as the tire/ground will give back. If your bike is throwing more force to the ground than the ground will put back (called traction) your tire will slip. This is not an uncommon scenario at least when I am mountain biking.

4. Nov 6, 2012

### lipster94

according to the manufacture of A.T.B. (absolutely the best) chain lubricants.
K. Lewis enterprises claims that the load on a bicycle chain is roughly 65,000 psi.
I dont know what procedure they used to come to this number.
just relaying the info.
Looking forward to some explanation!

5. Nov 6, 2012

6. Nov 6, 2012

### lipster94

i dont think he has a website.
his name is Keith Lewis and makes the lube himself.
I heard this over a phone conversation...

7. Nov 6, 2012

### AlephZero

You could skip all the guessing about force on the pedals etc, and just take the elastic limit of the chain material - i.e. the stress level that would stretch the chain permanently.

That would probably give a number in the ballpark of 65,000 psi, but I'm no expert on the material properties of bike chains!