Chain friction as a function of chain tension

Triathlon Forum
1

I assume that as power goes up there is more “tension” on the chain. If so does chain friction go up or down with the more tension ?

When pulled really tight I can imagine all the pins seeing maximum forces as they try and complete a cycle around the drive train but I can’t see to convince myself that lube plays a bigger or smaller role in this case. You might be just getting metal on metal contact here and lube plays a larger role at lower tensions when it’s not being forced out of the contact area.

I can’t seem to get a good mental image

2

I assume that as power goes up there is more “tension” on the chain. If so does chain friction go up or down with the more tension ?

When pulled really tight I can imagine all the pins seeing maximum forces as they try and complete a cycle around the drive train but I can’t see to convince myself that lube plays a bigger or smaller role in this case. You might be just getting metal on metal contact here and lube plays a larger role at lower tensions when it’s not being forced out of the contact area.

I can’t seem to get a good mental image

Yes, the more power (via tension) that is put into the chain the higher the loss of energy in absolute terms due to friction. Whether a lube, or specific lube for that matter, loses less (relatively) with more tension than its peers is really splitting hairs. We know lube by itself decreases friction and is good.

3

Thanks.

So let’s say I’m doing 100w and I’ve got 5 watts of chain friction ( just making numbers up ) that’s a 5% loss.

So now I’m doing 300w and I get 7 watts of chain friction that’s a 2% loss.

More total friction , but less percent loss.

4

I think the point is, use the best lube and you will get the lowest friction at any chain tension :slight_smile:
A very important issue in regards to lubes and friction is how prone a lube is to pick up dirt (or not pick up dirt)
From your example, a freshly lubed chain with 5 watts of friction could easily have 10 watts after as little as 50 miles of riding if the lube is a “gunk” magnet.
I highly recommend Lilly Lube, inexpensive, one of the top 4 tested lubes for low friction, and when applied correctly (easy to do), my chain is nearly as clean after 500-600 miles of riding as when I first applied it.

5

Hello 7401southwick and All,

Actual efficiency varies inversely with chain tension … In this study …

I think I saw a study by another group that found somewhat different results … YMMV

http://www.ihpva.org/...ve/PDF/hp50-2000.pdf

DISCUSSION AND CONCLUSIONS Tests of efficiency for the derailleurtype chain drive indicate that the overall efficiencies for the transfer of power from the front drive sprocket to the rear sprocket range from 80.9% to 98.6% depending on the conditions of drive operation.

Primary factors affecting the efficiency include the sizes of the sprockets in the drive and the tension in the chain. It was found that larger sprockets provide more efficient transfer of power while smaller sprockets proved to be less efficient. Simple, frictional loss models were developed that gave sprocket-size loss variations that agreed with those variations measured experimentally. Typically, a 2–5% loss difference was measured between the 52–11 and the 52–21 sprocket combinations depending on the drive operating conditions.

Experimental results indicated that the efficiency of the chain drive varied as a function of chain tension. It was found that the efficiency varied linearly with the reciprocal of the average chain tension with the highest efficiencies occurring at high chain tensions and lowest at low chain tensions. For example, the highest efficiency measured in the study, 98.6%, was measured at a chain tension of 305 N and the lowest, 80.9%, at 76.2 N.

It was found that chain-line offset and chain lubrication have a negligible effect on efficiency under laboratory conditions. Calculations of frictional loss resulting from offset indicate that this loss should be small compared to those produced by other mechanisms. This was verified experimentally. Lubrication effects on chain efficiency were tested using three different chain lubricants under a variety of test configurations. No significant quantifiable effect of lubrication could be inferred from these tests.

Infrared measurements of drive components indicate that frictional losses in the chain cause the chain temperature to rise during operation. This increase in temperature did not correlate with measured efficiencies under various conditions of operation. Infrared measurements on lubricated and delubricated chain links showed that the frictional heating did not depend on lubrication.

From the results of this study, it appears that the efficiency of the bicycle chain drive depends intimately on the chain operation as it engages and departs from the sprockets on the hightension part of the drive. Owing to the high efficiencies measured under high chain tensions, friction can account for only a few percent of the overall losses. Most probably, mechanical losses that are not converted to thermal energy in the drive account for the remainder of the measured loss.

6

Is chain tension in the report measured on top or bottom? I can see tension from the derailuer spring (bottom) helping reduce friction, were more tension from applied force (top) increasing friction. Differences may be negligable for both depending on lubricant.

7

**Hello dross and All, **

Top chain

I think ceramic speed and friction facts published some data also … (this is not it)

This drive is very cool looking and if it works will be a sea change in drives … and bicycle chains (and internal combustion engines) will be museum displays.

https://static.dezeen.com/uploads/2018/07/ceramicspeed-driven-bicycle_dezeen_2364_col_2-852x658.jpg

https://www.dezeen.com/...hain-eurobike-award/

https://www.bikeradar.com/...ivetrain-efficiency/

8

"Experimental results indicated that the efficiency of the chain drive varied as a function of chain tension. It was found that the efficiency varied linearly with the reciprocal of the average chain tension with the highest efficiencies occurring at high chain tensions and lowest at low chain tensions. For example, the highest efficiency measured in the study, 98.6%, was measured at a chain tension of 305 N and the lowest, 80.9%, at 76.2 N. "

This seems logic. If you bike with a certain power, the chain has a certain tension. If you change gear such that the torque you excert on the front sprocket increases, decreasing the cadence such that the power remains the same, the chain tension increases but the chain speed decreases. With a lower chain speed it is logical that the efficiency increases because the chain links rotate less per time unit relative to each other.
I think with the same chain speed but with higher chain tension the frictional losses in the chain are higher although the efficiency according to the definition in the article is also higher.

9

This is what I couldn’t rationalize in my head very well

As you loose tension in the chain I would think you can get more chain pin play ( tolerances and all ) and hence maybe more friction. As you get on the rivet , so to speak , you force out those small tolerance plays and maybe get less friction.

I could be convinced either way it seems. More friction with higher tension or less friction with higher tension.

10

Then everyone can have months or years of discussions on whether all those teeth flying around on that cheese grater creates more drag than what was saved by removing the chain 5W of friction.

11

hi 7401southwick
Yes this is confusing. As the chain tension (and rider watts) go up, then losses consumed by the drivetrain also go up in absolute terms, but they also go down in terms of percentage of losses and that’s because the increase in friction is not linear with load. This figure from my video on the ceramicspeed “3% faster” (https://www.youtube.com/watch?v=ryx5sDPkMUQ) might help? attached (also here: https://www.dropbox.com/s/nwtfsoz2exkln0p/drivenpower101.JPG?dl=0)

drivenpower101.JPG