Big vs Small Chainring - Same Power

power-meter

#81

And PowerTap pedals are supposed to handle non-round rings. They say “Non-round rings are supported perfectly with the P1. We are taking 40 individual angular velocity measurements and subsequently 40 power measurements per pedal stroke.”


#82

I’ve same preference, don’t like small rings at front at all. As you have said, I think it could be due to drive train losses, because being in the smaller front ring creates a lot more torque in the transmission that needs to be handled. It is my guess as well.

As for trainer, big ring gives the closest road feel for me, small one feels plain wrong. But, perhaps, this is different from trainer to trainer…

Also slower flywheel essentially needs to apply more braking in workouts, can this results in higher wear rate of both the tyre and the trainer? I understand the velocity is lower as well, but still? I only hear my tyre on the brink of slippage on the trainer when I am in the small ring.


#83

Nothing feels like climbing on the trainer. And big ring is closest to road feel for me. So I use big ring on the trainer and focus on raising sustained power output and vo2max power.


#84

The smoother power line is an indication of how well the trainer can modulate resistance to maintain the requested power level. On a small chainring, the trainer spindle is rotating slower, which requires a higher resistance setting in the trainer to deliver the power setting; on a large chainring, the corresponding higher spindle speed requires a lower resistance setting from the trainer. The ability to maintain the power setting (the presence or absence of wiggles) depends on a) how stable a spindle rpm you deliver (i.e. how stable your cadence is), which presumably would be helped by a larger spindle speed; and b) how tightly the trainer controller can adjust the resistance to maintain the power setting. It’s quite possible that the trainer has a easier time adjusting its load at a higher loading/lower spindle speed than at the opposite end of the spectrum.


#85

A bike drivetrain is more efficient with larger cogs than with smaller ones, assuming no chainline difference. This means that at a given power, speed and cadence combo, the large chainring + larger cog will be more efficient than the smaller chainring + smaller cog equivalent ratio. This is due to both the lower chain tension in the big-big combo, and larger chain bend radius, both of which reduce chain losses. This said, chainline differences can offset this efficiency: a perfect chainline small-small combo may perform better than a bad chainline big-big combo; lubrication has a big impact on that difference due to lateral friction between the chain plates and the cogs in a mis-aligned setup.


#86

Love this discussion - somehow missed this thread back in January and enjoyed reading through it.

I ride nearly exclusively in the little ring on the trainer because the lower fly wheel speed means I get quicker response times for short intervals - making my interval targets more accurate on things like Spanish Needle.

I’ve trained in both the big ring and the little ring and have tons of miles on flats and on hills but generally perform better on hillier efforts

All of this boils down to, I think, very very small differences in benefit and muscle engagement. Is anyone making the case that there are meaningful % differences in outdoor performance based on this, or is it all discussing very minute changes that can change your perception indoors, but would have, at most, an incremental impact outdoors?


#87

That is likely the one and only reason I would switch to smaller chainring. However I haven’t done Spanish Needle or similar workouts. What always puzzles me are theories that slower spinning flywheel results in higher trainer resistance, because what I feel on the pedals is “riding down a false flat.” My own theory to explain what I’m feeling is based on simple physics - small gearing has a higher torque multiplier.

Gearing on trainer having a significant impact on outdoor performance? I don’t know if anyone is truly arguing in favor of that. The closest I’ve read is some folks reporting large enough differences on the ramp test (big vs little) to make a difference in training targets.

In the real world I’ve done primary training for climbing events on the flats (50x19, 50x17, 50x15). In the process I developed the strength endurance to complete long 1+ hour climbs. This was before TR, and majority of training was in the flats, into a headwind, and relatively high gearing versus 34x32 or 34x30 on those long sustained climbs. And last year I did some big climbs and improved performance using TR in big gear. At least for these climbs, gearing for training didn’t matter.


#88

Agreed - and really, based on myself (and everyone else) using power match - this just isn’t the case. It might have a change in RPE but even that feels a bit doubtful to me

Me either! But everyone seems very passionate in defense of their position that I’m curious if they are actually taking the position that it has a meaningful change in their ability to do flat TTs or steep hill climbs or if it is truly a very small marginal gain


#89

the slower spinning flywheel may in fact result in the trainer applying higher resistance, but the lower bike gearing may be hiding it? I don’t know.

it is fascinating to read the flip side of what I’m feeling, from folks that use little ring.


#90

Just read through this thread yesterday and decided to give it a try in todays’ workout.
TL,DR: My experience pretty much matches yours @bbarrera.

I did Darwin today, 4x10 mins at Threshold. The first two intervals were done in the big ring (52-19), the next two intervals in the small ring (36-19). I changed gears around the 35 minute marker.

Apart from the obviously lower power variance in the small ring, the 3rd and 4th intervals felt considerably easier than the first two, even though I was already fatigued by that point. “Road feel” also changed noticeably. Sometimes it could feel like a wheel slipping on an wheel-on trainer after the switch.
Not sure what to make of this…


Darwin by bergfruehling, on an elite direto. Power source Quarq Dzero crank arm PM


#91

So then if you want to train different part of your muscles, and be ready for climbing and flat riding - change gears regularly.

I see the difference, and with each workout I change my gears to find how flywheel works and influence on my legs.


#92

Good to hear there are others experiencing the same. Are you using TR’s PowerMatch with your Quarq PM and Elite Direto?


#93

Yes, I use this setup with PowerMatch on all my indoor rides.

The actual power measured at the crank arm is very close across all 4 intervals in the workout above: according to TrainingPeaks I did 287W, 291W, 294W, 288W normalized for each respective 10 minute interval. So if the difference in RPE is not just imagined, the theories along the lines of muscle recruitment seem plausible (like @DaveWh’s explanation above, using variability in angular velocity as a starting point)


#94

Yes, I’ve seen the same with power measured at the crank arm being the same. The RPE difference is not imagined. My own theory is from looking at the ride data - the low RPE has smooth power with less variation. In fact the recorded power on trainer in low gearing is smoother than anything in the real world. The lack of variability could also be a reason for the difference in RPE.

Perhaps that is simply a non-technical way of saying “less variability in angular velocity.”


#95

I have no doubt at all that small ring is easier, I have often switched from the big ring if I am struggling with an interval or workout to the smaller ring to then be ok with finishing.


#96

I am the complete opposite. Have been training small ring since November and still when go up to big ring it feels far easier (at a given power and cadence). Is like the load is spread over more muscles and I just happily turn the legs.


#97

I train in the small ring, I’ve tried using the big and feel a noticeably increase in RPE. I have a workout coming up that includes 20min SS intervals so plan to change gears between them to see if any data supports my RPE assessment


#98

I wonder how much of this is down to the trainer type (wheel on/off), the trainer construction (mass of flywheel or of course virtual flywheel), people’s capabilities and riding style, or what you think it feels like?


#99

I’m not sure, probably trainer though.
I live in flat lands with zero hills so should be used to riding big ring but is opposite of what logic might suggest based on my riding


#100

I guarantee that trainer matters. Differences in flywheel size and functional rpm at a given gearing from the bike will lead to different results.

And rider type, prior training will also matter. Each has an impact on the RPE for sure.

I need to see if I can use the PowerTap P1 Pedaling dynamics to capture data like Shane did from his rotor. I’dike to see if I can quantify the max/min inertia differences since I have several trainers to test, wheel-on and wheel-off.