On a given bicycle, everything else being identical, would chain ring/cog of 52T/20T and 42T/16T, both yielding the ratio of 2.6, be equivalent in every way? Would there be ANY reason to use one set vs. the other?

Thanks for any comments.

The one with the larger sprockets will put less tension on the chain so, I suppose, it would wear the cogs a little less. I also suspect that's splitting hairs.

chainline would be one reason.

I would also agree, though I'm not sure if it's anything aside from psychological, that the smaller chainring feels easier to spin, even when talking about comparable ratios.

Yup and yup.

While we're splitting hairs... a 42x16 will weigh less than a 52x20 also... might even require a shorter chain.
And they're not EXACTLY the same gear ratio either.

edit: since this is apparently in reference to a SS/FG one might give a better chain tension with vertical dropouts.

smaller chain-ring has higher ground clearance ..

given 42t is a common chainring choice for cyclocross there are Chain guard discs made ,
to high finish standards to keep the greasy chain off your pants better..
put on in place of the 2nd chainring..
39:15 works too..

The larger combination will require a longer chain and will be slightly heavier and would have less ground clearance if you're going on technical trails. OTOH, it'll have less chain tension, should have greater durability and feel a bit smoother.

We were talking about this a few weeks ago in another thread. Well somebody mentioned the crossing chain that is not good but lets say that u can cross the chain just fine.

I think your question goes more focus to how they feel while riding. The ratio is almost the same if not the same but there are some differences in how the gear feels. The 42x16 will feel like you are dragging it, the 52x20 will feel easier to move but at the same time will feel like you can't go any faster, like pedaling in the air.

The reason for this is that the small cog and chainring have less torque than the larger ones, so you need to push more power to move the 16 cog (eventho 42x16 is a super light gear) than the 20. The nice about 42x16 is that you can accelerate with it because u drag it more than the 20, the chainwheel has something to do with is also.

HOw to decide what to use? it depends, is not good to cross the chain or ask andy schleck about it. So one factor is the bike, other factor is the rider, some guys can ride better with big cogs than with small cogs, other factor is the terrain. In short it depends on you.

If the gear ratio is the same,it's the same.The same amount of work is being done with the same amount of energy being appied.Doesn't matter what the gear sizes are,whether it runs through a jack shaft,whatever.The final drive ratio is what it is,doesn't matter how you get there.

The bigger the gears,the longer they last,per the same ratios.You have more of the chain transfering load to the sprockets.

Plus lower load on the chain and teeth.

Bigger cogs are more efficient. There's not much difference between 52/20 and 42/16, but you should notice a difference in smoothness and efficiency between a 52/13 and a 44/11.

em, P.E.

Ultraman's description is technically wrong. The same ratio is the same ratio no matter how it's gotten and will feel the same to the rider.

It's a very minute difference but the larger chainring/larger cog combination will be slightly more efficient as the chain is wrapped around larger circles but the advantage would require delicate instrumentation to measure.

Any idlers like jockey wheels are a bit of a wild card, cause they get smaller in proportion to bigger rings and have an associated drag.

This info is AWESOME! Just the stuff I was interested in. So from the above I gather:

1. 52/20 will be more robust (load spread over more teeth).
2. 42/16 will weight less (smaller components, shorter chain).
3. 42/16 will give higher ground clearance.
4. Jury out on what "feels" different.

Gotta do the experiment, two identical bikes, two "equivalent" (to the nearest 0.025 ratio) gear setups, one rider.... blindfolded.

A "jury" isn't needed. Physics is physics. Good luck getting volunteers for the riding blindfolded part of the test.