rbrides

How does human physiology and performance compare when pedaling in the big ring versus pedaling in the small ring, when cog selection on the cassette makes the outputs similar?

Example

Big Ring 48T + cassette in 32T cog produces

Gear Ratio 1.50

Gain Ratio 2.99

Gear Inches 40.04

Development 3.19 meters

Speed 10.1 MPH



Small Ring 32T + cassette in 21T cog produces

Gear Ratio 1.52

Gain Ratio 3.04

Gear Inches 40.67

Development 3.25 meters

Speed 10.3 MPH,



Nearly identical.



But what is the physiological effect on fatigue, endurance, power and overall performance generally? If I climb a few miles in one versus the other, will I just plain be more worn out in one versus the other?



Is there a difference in the “power” (I don’t have a power meter!)

datlas 

Should be roughly the same. Avoid big-big and small-small combos and otherwise don’t sweat it.

DaveSSS 

The 48/32 would be cross chained and not the best selection. The 32/21 is the better choice.

Every gearing setup has a transition speed where below that speed, the little ring is the better choice.

Ilbiker

“But what is the physiological effect on fatigue, endurance, power and overall performance generally? If I climb a few miles in one versus the other, will I just plain be more worn out in one versus the other?”

I don’t know. You will have to try these scenarios and see what the results are. Only you know your physical abilities and limits. I use both chain rings. Have 22 gears, might as well use them based on the current situation.

RChung

If the gear ratios are the same and the cadence is the same then your speed will be the same and your power will be the same.

(There are small differences in drive train efficiency so it's not *exactly* the same -- you lose a bit of efficiency with the smaller chainring -- but they're very close.)

Robert A

Physiology should be exactly the same since your foot experiences the same gear ratio. But the question I'm curious about is whether there's a difference in drivetrain efficiency. My assumption is that the big ring is more efficient because the chain doesn't have to "bend" as much. But I'm curious what others think.

Dean V

But wouldn't the greater inefficiency of the smaller sprockets quite likely be compensated for by the straighter drive line?

asgelle

It’s not a matter of opinion or something where majority rules. The physics says larger cogs will be more efficient. The question is how large is that effect and will it be negated by differences in chain line (which would not be a factor on a fixed gear).

datlas 

Of course there is a difference. But so small as to be insignificant.

Robert A

Why are larger cogs more efficient -- because the chain bends less, or another reason?

asgelle

Yes, because the chain bends less.

RChung

For the same gear ratio and same cadence, the small chainring-small cog combo chain travels slower than a big chainring-big cog chain. For example, a 39-13 and a 54-18 are the same gear ratio, so if you're pedaling at 60 rpm you're going at the same speed and producing the same power at the crank. However, in the 54-18 the chain travels 54 teeth per revolution, so 54 teeth per second, while in the 39-13 the chain travels 39 teeth/sec. You're traveling at the same speed, so the same power is going through the drivetrain. But the chain is traveling 38% faster in 54-18 than in 39-13 so the chain tension must be 38% lower. So in the small-small combo, not only does the chain bend more, it's also under more tension. That's why the old microdrive MTB drivetrains wore out faster.

RChung

We've measured differences in drive train losses. We know it wasn't chain angle because we jury-rigged a frankencassette with small cogs inboard of large cogs so the small-small combo had the same chain line as the big-big combo.

colnago62

On the track riders are moving toward large chainrings and cogs. I have seen riders with 60 tooth chainrings and larger on the front.

Amt0571

Drivetrain efficiency is noticeably better when on a big / big combination than on a small / small one. Personally, I can notice it by feel. It can vary if you're crosschaining a lot though, as crosschaining means a loss of efficiency.

If I'm in a point where both options are acceptable, I always ride the big ring unless I know I'll need to downshift to the small ring again in a few seconds.

rbrides

Many great comments. Thank you all for contributing.