Watts lost when your chain is on a cog that is not perfectly in line

Triathlon Forum
1

with the large chainring?

I do not have one of my bikes at hand. Can someone check in what cog space (counting from cap to hub) is the large chainring in line with a cog?

Yes, I am aware that this is an excess to some. :slight_smile:

Thanks,

Sergio

2

Starting with the 12 (12-27) my chain is dead straight when on the 6th cog up, the 17.

3

you guys have an SRM?

borrow a power tap and find out
you can borrow mine if you are in austin.

4

I was not expecting that the chain is straight on the upper part of the cassette. Thanks for the information.

Jack, No, unfortunatelly not in Austin. We use Quarq. I am in Mexico and Jr. in Switzerland. :slight_smile:

That sounds like a good idea if you do it carefully I guess.

Sergio

5

Quite a few people have looked at this. Testing (which I canā€™t put my hand on real easily) shows:

Chainline isnā€™t a big deal,just stay out of the extreme cross chain

For higher power (I think over 250 watts) go big, big chainring / big cog vs little little, under that power go little

donā€™t use a 11 tooth cog

Iā€™d assume 10/11 tooth pulley wheels would also be bad if the 11 tooth cog is bad, but that wasnā€™t specificallly tested.

Styrrell

6

Thanks Styrrel. Largest he can use is a 14 so I guess it will be no problem.

Thanks to all.

Sergio

7

interesting, the chain bend around an 11tooth crosses some sort of efficiency boundary?

8

Quite a few people have looked at this. Testing (which I canā€™t put my hand on real easily) shows:

Yeah, I wish I could find the study. We might be talking about the same one. It showed good data and outlined what seemed like solid testing.

A less-than-desireable chain angle on the big/big was still more efficient than the best chain angle on smaller chainrings/cogs.

It was at least .5% I believe, so we could be talking about 2+ watts in race scenarios.

-Physiojoe

9

A true real world test would have to also factor in the wattage lost by shifting to maintain an ideal alignment. Assuming there is some momentary dip in power when you shift on the front and back to maintain chain alignment, the ā€œwatts lostā€ is going to also depend on whether you are on a long run in one gear versus a situation where you may avoid several shifts by being a bit out of alignment for part of the time.

10

Thanks, I will have to remember this the next thread weā€™re quibbling over gearingā€¦ i.e., someone will usually say that thereā€™s no downside to a compact in front (or the corollary that going bigger like 54 or 55T is a waste) since a 50x11 is plenty tall, or on the flip side if you have a standard 53 (or bigger) in front then thereā€™s no use for an 11. As long as itā€™s a flat course, I run a 11-21 in back AND a 54T big, so I can spend as much time as possible in the middle of the cassette; the 11 amounts to a glorified spacer unless thereā€™s a strong downhill/tailwind (and I donā€™t need anything above the 16 or 17 except for rolling out of the parking lot to warm up, either).

Of course, this sort of minutiae doesnā€™t apply to the ā€˜set it and forget itā€™ folks who only have a one-size-fits-all crankset/cassette choice full-time and need to accomodate hills, too.

11

i would also like to know if being in the 11 loses ā€œ0.4 wattsā€ then maybe I donā€™t care

or if it loses 2 or 3 watts

in which case I need me some 58T chainrings
.

12

For the rare times where Iā€™m in the 50-11 and generating full power Iā€™m not too concerned about losing a couple of watts.

I have a compact and 11-28 cassette and I use pretty much all of the gears. Also apparently my tendency to do alot of climbs in the big ring and a fairly large cog is efficient (or so I surmised, I came off with the gist that larger cogs are more efficient, if Iā€™m wrong than please correct me. Iā€™ll take that trade.

13

The relevant articles:
http://www.ihpva.org/HParchive/PDF/hp50-2000.pdf
http://www.ihpva.org/HParchive/PDF/hp51-2001.pdf

The conclusion is that small rings and cogs are more efficient at lower power levels, and at high power there is little difference.

Cross-chaining made little difference.

14

You need bigger chainrings. This testing showed the difference to be about 5 watts, but only at higher (but reasonable for TT) power.

http://www.wattagetraining.com/forum/viewtopic.php?f=2&t=87&st=0&sk=t&sd=a

Styrrell

15

ā€¦and the difference in power between cogs is? :slight_smile:

Sergio

16

Road pros I have spoken to donā€™t worry about chainline except for the extremes, but they do say that larger cogs are more efficient. This is why you see the crazy large custom jockey wheels on Contadorā€™s bike (Lance used them too). Pros use 55 tooth big rings so that they are cruising on a slightly larger cog in the back most of the time, which means less chain bending and allegedly less energy loss. You are talking about lateral chain bend, though. A byproduct of the larger chainring would be that you are more likely to have a straight chainline on the flats, since you would likely be in the 55x15 instead of a 53x11.