Big vs Small Chainring - Same Power (ERG Mode Gearing)

Training
101

From reading comments, I’m sure trainer matters.

Rides out my door are flat with a lot of wind. Nearly all of my weekend group rides involve climbing, with at least one climb featuring 8-15% steep sections.

I’ve gone thru my power data and looked for outdoor rides with smooth power, shown earlier in this thread: Big vs Small Chainring - Same Power (ERG Mode Gearing) - #63 by bbarrera

What struck me the most is comparing power smoothness of:

  • big ring on Kickr 2017 (wheel off, direct drive)
  • best outdoor rides (both climbing and flat)

The “not so smooth” power of big ring on trainer in comparison looks artificially smooth compared to the steady power output segments of an outdoor ride. And the little ring on trainer has even smoother power!

In other words, the little ring’s power on trainer looks like a flat line when you compare to “smooth power” outdoor ride segments.

At least on my trainer setup, it seems the “this can’t be real” artificially smooth power in little ring has something to do with lower RPE - the “riding down a false flat” feeling that I get. It feels so wrong and unnatural that I can’t bring myself to use little ring on the trainer.

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102

I’m training for a 70.3 triathlon. I am doing my trainerroad workouts in the big chainring. For which type of workouts might it be worth dropping down to the small?

103

This is a great example, thank you for sharing. I’m in the middle of executing the same mistake, thankfully alerted to this by a recent GCN video on youtube.com about this very subject. I think your example really brings it home.
I am training for a week in the mountains and have been smashing about in the big ring, when, of course, I have no hope of using the big ring in the mountains!

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104

Just became aware of this discussion in an early Podcast episode, the very first topic covered in
Ask a Cycling Coach 26: Do Different Trainers Affect FTP, Body Fat Analysis for Females, & VO2 Max

Together with the chart for muscle recruitment that @GPLama used in his video, this starts to make a lot of sense.
muscleRecruitment

So I feel we can argue all day long whether big or small ring is easier - because it will depend a lot on what and how you’ve ridden in the past. The artificial/‘low inertia’ feel of riding the small ring on the trainer is actually very close to what I ride outside: Either doing weekend outdoor rides focussed on climbing or commuting by bike with artificial braking (pulling a trailer and having a child seat on the back for added drag). So it would make sense for my muscles to be conditioned in a way that training in the small ring would feel easier to me, but not for someone who is used to different kinds of efforts.

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105

So being thoroughly confused and this thread having no consensus, what do us one-by guys do? We are always in the Small Ring which is 32 in my case. I’ve historically been using 32 x 16 on the trainer. My experience on the Kickr Snap (wheel on) is that it likes a higher cadence 90+ rpms and is best (less RPE) at 95-105 rpm.

Due to all this discussion (and having my FTP set too high) I’ve gone in search of a better RPE. Yesterday I did Pettit +1 at 32 x 21 and I THINK it felt better, but I’m not sure :man_shrugging:. Today is over/unders so it should be a real test.

What are your thoughts on gear setup for those that ONLY have a small chainring and the rear cog is their only variable? Does this change whether you’re wheel on or direct drive? I ride MTB only, so does that come into play?

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106

Sure, it some in to play. To oversimplify it,you might try using the same gear as you use on the majority of your ride.

Overall, the idea is to select a gear that gets close to the inertia you feel outside, so you are loading the muscles in a similar way.

With 1x, you still have a nice range. Super low on the bottom, which will be very low inertia. And the high is likely still quick, but well short of a road setup. I don’t see that as a problem.

I think you need to experiment as each rider, trainer, and real world need will vary. But I’d start with some intervals 5 mins or longer and try some extremes in the gear range to see how they all feel.

For MTB, my gut tells me you shout be mid cassette and up or down by maybe 3 gears to play with inertia.

107

IMO all you should worry about is keeping your chainline straight, assuming that combination works well with your trainer power floor/ceiling.

108

The trainer power floor/ceiling is a significant issue in some cases. I’m geared long (7-sp antique serves as my trainer bike, and 39x21 is my shortest), and I have quite the floor issue on a Tacx Flux S: cold, it gives me 135-140W at 90 rpm on that low gear, and this improves to approx 115W when the unit warms up. So unless I shift at every interval, I end up riding the 39x21 all the time.

I’ll address the problem as soon as a bunch of parts coming my way land home and I have the time to do a cassette + brifter swap on my faithful basement ride.

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109

I continue making “the same mistake” and yet (just one example) at end of week5 in SSB1 (big ring 50x15) achieved personal best HC climb on this 18.1 mile @ 5% (4500’) segment. Maybe the laws of trainer inertia don’t apply in my garage? :thinking:

Maybe, just maybe, gearing on the trainer is far less important than simply training for the demands of the event.

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110

Gearing on the trainer(in erg mode) is very important depends on the kind of event you take part.
XCO biker more often use less flywheel interia, road biker need both. You shoud change your gears to find how your muscles work :slight_smile:

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111

I, too, am still scratching my head at this one.

It seems that two groups of people are genuinely each having exactly opposite experiences with small vs big ring in ERG mode.

Group 1 finds the big ring takes less effort to maintain a given wattage and cadence,
Group 2 finds the small ring takes less effort to maintain the same wattage and cadence

One acid test of group 1 is (for example) that they can achieve a higher FTP using the big ring. This is not an imagined thing, it is a very real difference in physical toll on the body, muscles and cardio-vascular system in each case (big vs small). A few anecdotes on here confirm this phenomenon.

For me, today was a good case in point for group 1:
Lamark, 4 x 10 minutes right on FTP. In my case, 265. Gear was 50-16. I JUST managed to complete the workout, all of it at 95-100rpm, with the exception of the last 2 minutes of each interval that were grinding at 85-90, where I was struggling badly to avoid the black hole. I know from experience that there is NO WAY that I would have managed the workout in 39-16, it would have taken a far harder effort keeping the pedals turning and I would have been beyond my personal limit.

On something though, I think both groups can agree, and this is where you make a very good point about the torque multiplier effect of lower gearing. For intervals such as 30/30s (eg Gendarme), the superior torque multiplier effect of using the small ring means that I always use the small ring for such workouts. In fact in the big ring not only are big wattage changes over short time periods difficult and ineffectively achieved by the trainer, the wattage floor in the rest intervals can be achieved only when in the small ring. In the small ring the actual power chart follows the target very precisely, with virtually no lag (I have no searate power meter which helps in this respect).

Another thing I agree on, by the way, which I haven’t mentioned, is that I MUCH prefer the feel of riding in the big ring on the trainer in ERG mode. It much more accurately resembles road feel across a wide range of cadences and I use the big ring most of the time for most workouts. I’ve been actively trying to address the “big mistake” I made last year (ie becoming much stronger on flat riding and not so much gain on hill riding strength) not by always selecting the small ring but by resisting the temptation to ride at 95-105 rpm, because by doing so I’m missing out on proper strength endurance workload and leaning too heavily on my cardio vascular system. In fact I actively dislike the feel of riding in the small ring for extended periods; it just feels kind of wrong.

For reference I’m on a Kickr Snap wheel-on in ERG.

The mystery continues!

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112

You’re absolutely right, as long as each workout pushes you physically and mentally as close to your limit as appropriate for your goals, then it doesn’t matter what gear you’re in! :grin:

113

No need to scratch your head. There is a simple explanation!

While there are (may?) be differences in muscle engagement between the large and the small ring - they are, it seems, too small to have a significant affect on your outdoor riding.

I asked this very question much earlier in the thread and the consensus was that they don’t think it will have a significant impact on outdoor performance.

Where it (could) have a significant impact is in RPE indoors. However, if you’re putting out the same power it is truly just RPE, not actual fitness

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114

Yup, fascinating. I put this phenomenon into the same category of individualization as knowing that long sweet spot intervals are easy for me, but hard for others (and vice-versa, I struggle with 3+ minute vo2max intervals @ 120%). I usually find it pretty easy to modulate power on 30/30s in the big ring, but also recognize the little ring is easier to jump from low to high power.

My key takeaway is that it pays to experiment with big vs little chainring, find what works best on your trainer setup and use it.

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115

Tried 32 x 21 gearing doing the over/unders in Fang Mountain +1 today. I think it felt better than my previous 32 x 16 gearing, as if I didn’t HAVE to stay on top of the pedal stroke as much. Low 90s rpm used to feel like pedaling in mud, not so much now.

116

To make matters even more convoluted, I find my perceived exertion is lower at lower candences (70-80 rpm) than at higher rpm (90+ rpm). There is this one workout that I can easily finish at 70-80 rpm (I need to vary the rpm to get the desired power output) whereas at 90-100 rpm I was not able to finish the workout. Perhaps that‘s because I come from the MTB-side of things where in my experience the cadence tends to be lower, I don‘t know.

117

Reading this thread, and facing 3x20 mins of SS boredom, I thought - hey, let’s test this out. I normally do most of my training on 39x21 (my lowest gear, don’t ask). So in the middle of one of the SS intervals, switch over to large (50) to see what will happen… woah there, much harder, what’s going on? Took me almost an entire minute to realize I was riding on the trainer’s floor and pushing 30W too high. Oh well. I did most of the intervals back on 39x16, a classical flat road headwind solo ride place for me. Can’t say I saw a difference of perceived effort.

118

@bbarrera, I know you’ll find this interesting. I’ve appreciated your own analyses on this subject so I thought I should do one myself instead of just expressing opinion and anecdotal evidence!

If any readers don’t want to read this whole essay, I’ll cut to the chase and summarise the post – following a test of the theory, I present here proof that for a given target wattage and cadence, in ERG mode, riding in the big ring makes it easier for you than using the small ring*****.

Many of you will be familiar with the peculiar phenomenon that pedalling in a higher gear (big ring) when in ERG mode can allow you to use less energy to maintain a given target wattage than if you maintain the same wattage at the same cadence, in a lower gear (small ring).

This can be illustrated by watching the effect on heart rate of changing the front ring mid-interval, and feeling the corresponding change in RPE.

The logical consequence of this is that your own personal level of “maxed out” in respect of the energy you are expending, your measured heart rate and your RPE, can allow you to maintain a higher target wattage if you select the big ring, compared to the small ring.

The final strange consequence of this is that if you do the ramp test in ERG mode, you can survive the ordeal of pedaling to your absolute limit up to a higher indicated target wattage if you select a very high gear. And by the same rule, a lower maximum wattage if you select a lower gear.
So in this translates to: big ring = higher FTP, small ring = lower FTP.

***** CAVEAT – the above applies to some trainers, possibly not all. My own is a Kickr Snap but others have reported the same phenomenon. My own set up does not include a separate power meter nor power matching. *****

So I finally got round to testing this phenomenon. I chose the workout Beech and selected the last interval, a 14-minute steady effort at 75% FTP.

I did half the interval in 39-16 and half in 50-16. I selected the middle 5 minutes of each 7-minute section for my test sample, to eliminate any spikes caused by gearchanges and “getting on top of” cadence after a gear change, etc.

I held a steady 95rpm cadence for the whole 14 minutes.

Observations:

  1. The main takeaway is that it proved the theory, unsurprisingly. HR was higher for small ring, as was RPE.
  2. I selected small ring for the first half and big ring for the second half, so that there would be no risk that the higher HR in the small ring might have been interpreted as merely attributable to mounting fatigue at the end of the workout.
  3. This is the interesting and powerful observation: fatigue was clearly mounting during the small ring first half, with a HR trend going upwards, then when we got into the big ring second half, the HR was not only lower on average but trending downwards, clearly demonstrating “active recovery”.
  4. It may look like “just a few bpm” but the differences are significant and can be very much felt in RPE. They are certainly enough to extrapolate into higher FTP results for the same HR and actual exertion in a ramp test.
  5. I suspect that the same test done at say 90% FTP would produce even more marked HR differences, as you approach your physical limits.

Notes on “road feel”

  1. As always, for me personally, the big ring felt more like road riding, more realistic and somehow more pleasant.
  2. The weird thing is that the small ring, as my friend on here has previously reported, felt a bit like riding “down a false flat”, but despite this, and somewhat counter-intuitively, it was clearly taking me more effort to pedal in this gear.
  3. It felt easier to keep cadence steady at 95 in the big ring.

As I have said, this is ERG mode, wheel-on trainer, no separate power meter or power matching. I’d be interested to see a repeat of this test with the same protocols but done with different hardware.

I’m acutely aware that none of this actually matters really, except to illustrate that if you ride on this sort of set up, the absolute FTP number that you quote will depend on what gear you happened to ramp test in. The only real practical takeaway is that you should probably test in a similar gear to the gear you generally work out in, at least for threshold type intervals.

The attached summarises the data.

Trainerroad%20gearing%20test
Trainerroad%20gearing%20test1280×720 143 KB

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119

I would be interested in what would happen if you ran that same test but passively listened to an accurate, calibrated power meter simultaneously. Just to see if the root cause is the trainer measuring power differently at different flywheel speeds or if there is some physiological component.

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120

That! I think it will be harder, I think my HR will increase, I believe RPE has increased … Results: HR increased. Was it a self fulfilling result? :man_shrugging: