Big vs. Small Chainring question...
 

I think this might be a stupid question (if it is, please be kind!), but I'll ask it anyway because I'm curious.

Theoretically, if you can get the same gear inch by using either the large chainring with a large cog, or small chainring with a smaller cog, is there any difference in efficiency? Any reason to favor one over the other?

The reason I ask is because when I'm riding flat terrain, with my 11 speed cassette I often have a choice of large or small chainring and wonder if there is a reason to choose one over the other (other than fine tuning or simply because it's the chainring I happen to be in).

No real difference.

But here's some info on Chain suck that may be of interest: http://fagan.co.za/Bikes/Csuck/

Whatever results in a straighter chainline.

Big rings put less tension on the chain and therefore less on the frame. It used to matter more on flexi frames. It mattered a lot on the tandem with the horse I had on back. Still I opted for a 36T inner over a 34T for hill climbing (then bigger in back) due to the tension part in buying a crankset last week.
As mentioned - chain angle also matters. So not unusual for a TT person to use a big ring like tony Martin did - 58T Pro bike: Tony Martin's Specialized Shiv TT | Cyclingnews.com The junior kids did this too for TTs moving the smallest cog more to center.
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Yes.

I think cross chaining can also cause more wear on the rings, and increase risk of a chain being pulled off of a ring under load (and wear?)

Not exactly.

If the gear inches are exactly the same, then the chain tension would be exactly the same. Perhaps only a very slight difference in torque distribution on things like the bottom bracket (chain closer or further from fulcrum).

Smaller gear inches and spinning faster can still put the same amount of torque at the rear wheel, but one can get more even power distribution (a big advantage for loose gravel/dirt).

Rumor has it that heavy bike (tandem?) with very large sprockets on the freewheel can get them especially tight for a difficult removal.

As mentioned, cross chaining might increase wear. There may also bequicker wear on the smaller sprockets than the larger ones. However, many manufactures use a mix of steel and titanium/aluminum on the cassettes which will even out the wearing a bit. The larger front chainrings will also wear slower than the smaller ones.

Some people have suggested a slight loss of efficiency with the smallest of the rear sprockets (9,10,11T?). Any efficiency loss likely becomes quite minimal after one gets up to maybe 15T or so.

For me its performance related. If I'm getting into the hills I will work off of the small chainring. If we are getting ready to haul butt, I go to the big ring.
It stinks when you're haulin' and on the small ring and you run out of gears out back.
Also, may times I stay on the bing ring and stand to make it over the top of a hill. It can be faster.
One of my favorite ratios is the big ring up front & 2nd or 3rd in the rear. That can be a little noisy, but it gives the opportunity to accelerate out.
YMMV

For the foot and the tire - it is the same. Not for the parts in between.
100lb force on the pedal puts this tension on the chain:

175mm crank arm 36T ring (70mm radius) - 250lb chain tension
vs
175mm crank arm 52T ring (100mm radius) - 175lb chain tension
Is just a different lever bar/fulcrum.

The drive side chain stay and BB spindle is taking the compression. I'd rather have 175lb than 250lb.

I love science. ;)

I have read that it is technically more efficient to have the most teeth contacting the chain. This was specifically in relation to SS gearing, where it was determined that more teeth = more efficient, despite the slightly increased weight. Personally, I didn't understand the physics when I read it, and would think more contact area would mean more friction, but apparently that is not what was determined. On a geared bike, however, I would agree that whichever combo gives the best chainlinewould be best.

One of the arguments I've seen is that by using a bigger gear, each adjacent chain link doesn't need to bend as far to get around the gear, and thus there is less friction in the chain.

One thing I've noticed, which oddly, is rarely mentioned, is that the small ring is quieter across the range of the cassette.

In order to get a quiet drivetrain in the big ring, I have to be in the highest 4 gears, which on the flats, I'm rarely in.

Compacts are frustrating for my type of riding: solo rides on flats. I'm usually in the higher gears/small ring, or lower gears/big and wind up doing a lot of double shifting.

As much as I despise 1X, I could see the utility of it with a 12 speed in the back.

12 13 15 17 19 22 25 28 31 35 39 44 X 48?

Doesn't seem too bad. And my front shifting is pretty darn good.

Big ring means less friction up until the point the chain line gets too bad. People actually measured this to determine the optimal shifting pattern:

Friction Facts: free speed from proper shifting - BikeRadar

What is a "big ring"?

fify

Thanks - just edited it!

Sur le plaque

Velominati ? The Rules

Try a CX crankset or rings, 36/46. 36 will get up to 20ish before spinning out and 46 helps stay in the outer edge of the cassette while being easy to start from a stop. My cross/road-ish bike is 36/46, the road bike is 36/52 (which I may change to between 46, 48, or 50 on top)

Its no longer a stupid question...:)

Not as far - but more of them bend. So around the front ring, the net bend is the same if it is 24T or 52T.
Same with cassette. Each bend will be greater around an 11T than a 25T.

What matters is the static friction to start bending. You could say if there was much, then bigger is worse because you have more links starting to bend. But, lubed correctly this does not seem to be something that matters in testing.

Repeating - what does matter a bit is bending friction on a 250# tension vs 175# tension. Generally on the pin/roller leaving the rear cog and hitting the big ring. But on a worn setup this is distributed to the next teeth - but less force on each tooth.

Cadence could matter too. 120RPM vs 80RPM - but at same power the 80RPM has more tension on chain than 120RPM - so all hard stuff to figure out and the FrictionFacts guys did not test every RPM, and tension and ring diameter. So you have to guess a bit and some chains are lower friction than others due to materials and coatings. I like bigger where I know chain tension is less, but too hard to know the rest.

its Mathematical, not theoretical. example: you can get the same 4:1 gear ratio with several sets of numbers

52:13

48:12

44:11



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