what are the benefits or differences in having a larger front chainring (50t+) vs a smaller front chainring (42t) if you are able to keep the gear inches approximately the same through varying sizes of rear cogs?
For example if I run a 44t chainring and a 15t rear cog I end up with about 78 gear inches. Is there any difference if I run a 49t chainring with a 17t rear cog for 76 gear inches? ( I was just trying to come up with gear inches that were approximately the same)

Chordal Action

I never knew about chordal action! that's good to know.

Any idea on how much it is affected by less than 10 teeth difference in the chainring? The math is too much for me to understand from the diagram I saw, but if you have any thoughts I'd love to hear it!

For most of us, the differences are so slight as to be a matter of personal taste and aesthetics. I personally think a large rear sprocket looks ugly and a small chainring looks purposeful, but there is no logic to that. It's just the way I feel.

In theory, larger front and rear cogs to get the same ratio gives you a little bit less friction, a little it less chain wear, a little bit more weight and a tiny amount more aerodynamic drag. You may also consider things like clearance if you ride on rough ground.

But unless you are riding at the highest level, looking for marginal gains to make the difference between gold and silver, the amount of water in you water bottle, or the number of keys on your key ring in your pocket probably make more difference.

I run 46/16 on one bike and 52/19 on another and the ratios are roughly the same. Smaller chain rings wear out faster but are lighter. Larger chain rings are the opposite..

yeah okay, friction make sense to open up the tight bends that a smaller chainring and cog could create. Thanks for the input.

Scroll down to "Big or small?" in Sheldon Brown's article H E R E

He gives a nice explanation, complete with a handy table showing the pros and cons of big and small gears.

Of course Sheldon Brown has the answer! I just can never sift through all of his mounds of information! Thanks for your help

This.

Last time the question came up in here, I got into it with a forum member whose name I forgot. We probably both overstated our opinions. But he insisted getting the biggest gears possible would make a noticeable difference in efficiency. I'm sure you can get greater gains by tweaking your tire pressure a few PSI.

I think you have a point. From the other articles it seems that the change is small enough that it wouldn't make much of a difference and it could be found in other places (like PSI).

It really makes the most difference for clearing obstacles on a mountain bike, or for frames with clearance issues on the chain stay.

I plan never to get drawn into an argument in a forum these days. I say what I think, read what others think, and sometimes learn something from it.

I am about a stone overweight which means I need to lose nearly 10% of my bodyweight. Worrying about making the bike 5% more efficient would be ignoring the elephant in the room. There is a point of view that a less efficient bike means more exercise during the short time I have available to ride it!

I ride 42/16 at the moment, with an 18T on the other side of the hub for harder conditions. It suits me. I can't help noticing that, without exception, the Olympics riders have adopted a somewhat different approach!

With some single speed frames the chainstay clearance with the chainring is part of the equation. Some can't fit larger than a 42 for example.

I think most people just end up using whatever spare chainring they have laying around that works.