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

I have been struggling to try to understand the power differences I get between my Stages L/R power cranks and my 2017 Wahoo Kickr (see Power mismatch -- Wahoo Kickr vs Stages Cranks). In a nutshell, I am seeing a greater than 10% difference (with Kickr being higher) between the two power levels when doing TrainerRoad intervals in ERG mode. When just riding on Zwift in SIM mode, the power levels seem to be much closer together.

Well, I had been doing all my TrainerRoad workouts in the big ring (53-14 or -15). So, after reading through this thread, I decided to do today’s workout (Antelope) in the small ring (39-17 or -19). Well, in the small ring, the Kickr and Stages power levels were very close to the same! I did the last interval in the big ring, and the big difference in power levels (with Kickr being higher) returned.

Subjectively in that last interval where the Kickr power level was higher, I felt like I was actually putting out that power level. But there were also times when I felt like there was a bit of almost “coasting” going on when I overshot the target power and the Kickr was adjusting.

I haven’t done an FTP test in the small ring, but I have done the tests with Kickr power versus Stages power in the big ring. With the Kickr I was at 237; with the Stages, I could only manage 202 (though I was not in as good a shape, but should not have been that different!).

2 Likes

I did the exact same experiment one month ago during a Ramp Test on small ring. Have used DC RAINMAKER analyze tool to compare data of Powertap pedals, Stages (Left only) and the KICKR 2016.

https://analyze.dcrainmaker.com/#/public/f453550c-b6e5-4e8d-4f27-2bd454eb8f17

Don’t take care of Stages data. There are higher than the Powertap for a simple reason : I put more more on the left leg, except at high intensities. But if you compare Powertap (ELEMNT BOLT 73DC-216-12.fit) with KICKR (Ramp Test-2.fit), you can see that the KICKR drift at the end a lot. Don’t know if it happens on big ring as well however but maybe the KICKR take into consideration the fact that it retains pedalstroke or something on small ring ?!?

After some time adjusting going from 39/19 to 53/15, my cadence has dropped, also feel i use my leggs more (got a few days of stiffness). But my FTP seems the same.
I use Tacx NEO
I do feel that higher gear is more right for me. Outdoors i have about same watts on flats as in climbs (I think).

To add to your statement, can you tell us if you’re typically better at climbing or riding on the flat relative to others you size and power?

I just did set my venge up on my neo 2 to be able to compare my outdoor vs indoor watts and it turns out the s-works power cranks are consistently reading 10-12 watts higher on the small ring and 18-20 watts on the big ring.

I suppose it’s to be expected for the trainer measure a lower wattage. Did you guys experience something similar?

Varied power measurement from low flywheel to high flywheel speed is documented on a couple of trainers. The Neo (not sure the specific models proven) and H3 for sure. I can link to videos showing the testing and data (from Tariq Ali and Shane Miller from what I remember).

So, it’s a known issue that faster flywheel speed leads to divergence from “real” power meters on at least some trainers (and pretty likely more).

1 Like

Thank you for the quick answer. I watched the video but was suprised still the difference is this big. 20 Watt is quite significant.

So it’s been reported by a few here that training exclusively in the big ring negatively affected their real world climbing ability, but what about the opposite? What if I’m training specifically for triathlons with pancake flat bike portions, any negatives to training exclusively in the small ring indoors?

2 Likes

N=1 for me:

  • I trained 75% or more in the 34x17 combo the last 3 seasons on TR.
  • I do add plenty of standing breaks at 50x17 for comfort and to change muscle loading.
  • I also using 50x17 (and similar ratios) for “low cadence / high force” work to replicate climbing.

And despite that “low inertia” focus, I have had increasingly good results on the bike legs of my duathlon events. I also had decent results in my road events (other than some bad strategy decisions in one) in the same time periods.

I am experimenting a bit more this winter (spurred from these discussions) and trying more high flywheel speed training. I can’t make any claims other than I can “tell a difference” in the feel of the differences. I don’t know if there is any “negative” from the low speed training for high speed users. Pretty impossible to know without more good data or personal experience, unfortunately.

I can’t say that I feel I am missing anything specifically, but I am experimenting to see if I notice any differences rolling into this season.

Edit to add: I am 5’-10" and 145 lbs on a “loaded” day (about 3.9 w/kg), so that likely impacts my experience inside and outside.

2 Likes

This topic seems to be very personal and individual. Personally I think you should experiment and go with what feels right.

FWIW out the door for 6+ months of the year it is pancake flat but brutal headwinds, my favorite training route and weekly Wed night worlds feel like a 60 minute climb in the nearby mountains. And on Wed night when fitness is high I usually put out more power on the tailwind return. I’ve had very good success using large chainring on the trainer, for both these flat/windy rides and long climbs (1-3 hours) in the Sierra mountains.

1 Like

+1

I exclusively train on small ring (36) on TR, mid-cassette on the rear. Only to limit noise and vibration (Wahoo Kickr). I am a all-rounder rider, like to climb, like to put big watts on the flat as well. Feel VERY comfortable on steady pace efforts outdoor at 85/90% FTP, including on flat.

Don’t know if it is related to training on small ring indoor, but I like low cadence a lot outdoor. I train around 90-95 indoor on TR, but most of the time around 70-75 outdoor, even on flat section. Feel like I try to find the same kind of resistance with big gearing on the road. If it’s ok to be above 90rpm for me on TR, I feel like I loose “control” on the road above 85rpm. Weird.

Regarding numbers, my outdoor FTP/abilities follow(s) the same curve as my indoor FTP, no matters the gradient, etc

1 Like

Yes, I noticed that.

Slightly different muscle utilization.

I would switch to the big ring. It’ll take a few sessions to get used to.

Yeah, it makes sense to train to your most relevant strengths

What I’ve noticed with the Wahoo Kickr and Vector 3 dual sided peddles.

10 min warm up then perform a spindown calibration, and calibrate the peddles.

Today I was doing taylor -1, so VO2 intervals with the peddles on the garmin, trainerroad on the kickr. The warm up and first 2 intervals (of the first set) are on the big ring, from there swapped to the small ring as the power was 10% down, target 330, actual 300ish. Dropping to the small ring actually made things worse initially.

What you do see from the data though is that as the trainer warms up the 2 power meters gradually come back into line, after 26 minutes riding time they’re both reading almost exactly equally. My surprise here is how long and how hard you have to work it before the trainer warms up. I’ve felt something was a bit out now for a while, looks like it’s solved.

Thursday is SS, so I’ll do some back to back with big and little chain ring there.

A lot of the data here relies on the assumption that trainers measure power in a consistent manner regardless of spindle speed - a pretty large leap of faith. I have a lot more faith in the tests that include an independent power meter than those which don’t.

Given all this (ie flywheel speed affecting power accuracy) it’s hard to see how most trainers meet their claimed accuracy. I have not seen any statements from a trainer manufacturer that details what testing methodology they use to generate these claimed accuracy numbers, but it’s clear that some of them do not include testing a range of flywheel speeds.

1 Like

Elite trainers, Drivo, Direto, and Suito (not positive on this model) are only trainer that actually uses a power meter (optical). They use a German laboratory Physikalisch-Technische Bundesanstalt (PTB) for testing and certification of their accuracy claims, see Elite Drivo Trainer In-Depth Review | DC Rainmaker. Wahoo gen 1 had a stain gauges but they had problems.

I use the small ring in the middle of the cassette. I have completed 3 ramp tests with this now, I am considering moving to the big ring, for erg work outs now. For a ramp test, shall I always keep them in the small ring now?

I am thinking of moving to the big ring for more of a road feel, and helps with my cadence. Plus this helps with wear and tear on my gearing.

1 Like

Ramp test with what gearing you want to do the ERG workouts in. If I do a ramp test in Big Gear, then my FTP is 15 watts higher than if I did ramp test in Small Gear. YMMV for you if you do a ramp test both ways. In the end - keep your workouts and ramp test on same gear (Big vs Small) so you get the stimulus you are looking for without undershooting/overshooting FTP. Also, I would recommend Small Gear if you training for MTB. It will make a difference since we have less inertia in MTB.

2 Likes

Thats what I thought…I noticed a few watt increase when using the big ring. I don’t want to over shoot my FTP. I mean I want an increase but I want to be able to finish work outs.

The small ring is also quieter. Would using the big ring in work outs be more “realistic” feel though?