During the pandemic to now, my cadence when doing indoor workouts on my Stages SB20 has slow dropped. Now when I ride the SB20 my cadence naturally falls to the low 80s, no matter the workout. If I mentally concentrate I can keep my cadence in the low 90s, but this takes more mental focus, increases the RPE, and makes the workout more physically demanding.
Outdoors, my normal cadence is 90s (not including hills), and my SB20 is setup using the VeloAngle to match the position of my road as closely as possible.
Any thoughts on what would cause this drop in cadence over time? Thoughts on getting the cadence back up indoors?
How is your general fatigue? Have you added in additional training stress (such as lifting with your legs) that may be impacting recovery? How is your sleep? Has your FTP dropped?
Lots of things could be the cause. Interesting that outside has stayed consistent in the 90ās but inside has dropped. Hope you get it figured out!
I noticed recently that my avg cadence has dropped 10rpm or so. I suspect it has to do with me removing cadence from my main screen as I mistakenly assumed Iāve been cycling long enough that my natural cadence wouldnāt really change. Iāve been reading up on improving my VO2 workouts, and saw lots of posts about keeping rpm high (110+), which feels really high to me, so I got curious and added cadence back to my primary ride screen and was really surprised to see that Iām frequently in the 70s or low 80s, whereas I used to be in the 90s most of the time.
Iāve also seen my cadence drop over time, in the past found my cadence decreased with fatigue but got in the habit of āmusclingā through workouts and now it seems like it might be an issue. Something I hope to work on this fall and winter.
Do you think it could be something to do with the resistance you face when pedaling indoors vs outdoors?
Getting the right āflywheel feelingā might help you pick up your cadence a bit. It could make you feel like youāre riding along a slight downhill or with a tailwind, which is usually when I find myself pedaling at a higher cadence.
That said, keeping your cadence in the 80s isnāt super low and not necessarily bad, so you may not need to worry too much about it.
Outside my cadence is pretty low and would usually be max 80rpm on a flat / rolling route. Inside and using ERG mode I would always be somewhere in the range 95-100 average for the entire workout. Doing hard VO2max intervals I would always be over 100.
This is not intentional, the intervals are easier for me in ERG to maintain a high cadence.
When I switch to Standard mode I would be closer to my outdoor cadence but still 5-10 higher.
I think you will naturally adopt whatever cadence gets you through the workout easiest if not consciously working on cadence drills.
I wouldnāt necessarily see it as a problem but maybe start doing bringing some high cadence drills into your workouts.
I think flywheel inertia vs real inertia may be related here, as mentioned in other discussions about deltas between inside & outside. Notably with these smart bikes, there is a single gear ratio that drives the flywheel. Meaning that for any given cadence, the flywheel RPM will ALWAYS be that same value, regardless of the power / resistance applied.
That is potentially different when compared to bikes + trainers since itās possible to hit power values at a range of flywheel speeds. This can be manipulated to suit the rider preference (within the limits of the trainer at least) in a way that is not possible on smart bikes with fixed gearing. From my testing and that relayed by others, I think this inertia aspect is worthwhile of consideration despite being overlooked much of the time.
Not enough info is readily available related to the inertia issue, but I wish we have more concrete info on the relative differences between trainers and various use cases outside. I consider it parallel to the discussions about generating power on flats vs hills. There, as in trainers, itās possible to match power but have a different feel at the pedals and I believe that difference can show in cadence preferences as well as longer term fatigue.
I normally ride the SB20 in ERG mode when Iām doing structured interval workouts. Iāve wondered about the inertia question, but being on a smart bike inside I donāt have the ability to vary the inertia except via cadence. The intervals feel easier muscular when done at a higher cadence, but higher cadence feels overall harder / requires more concentration and I end up falling back to lower cadence and āmusclingā longer (e.g., over 1 or 2 minutes) intervals.
The inertia question is actually one I have with both the Zwift Ride and Elite Square: what gear combination do these use? Especially the Elite Square as the design makes it look like the front āchainringā is pretty small.
No time to look now, but I am pretty sure Shane Millerās deeper dive on this identified the front chainring size and I believe rear is still 14t like the original COG.
Iād see if DCR or Shane have these documented too, because I doubt Elite bothered to publish it.
As a guess for both, Iād bet it is close to a 2:1 ratio in both cases.
2:1 seems awfully low / will generate low inertia.
The āmost accurateā and ābestā feeling trainer - Velotron - used a huge (62 tooth) chainring. Iām not sure what size the rear COG was, but using:
14 tooth gives a 4.4:1 ratio
15 tooth gives a 4.1:1 ratio
So wondering if using a much larger ratio would improve the feel of trainers. Or is it that āmodernā wheel off trainers donāt have strong enough control systems to handle large (4+:1) gear ratios
Keep in mind the fact that the Velotron is a single-speed setup with direct connection between the cranks and flywheel via that single ratio (whatever it actually is) but 4:1 for easy discussion.
Your SB20 is more like the Velotron above but I have no idea what ratio is without some digging.
The consider the typical smart trainer setup that is a 2-part system.
Bike gearing from front chainring to rear cassette cog will be one ratio (big gear driving small gear). 50t x 11t = 4.5 for the big swing, 34t x 17t = 2 as my daily ratio.
The trainer takes that rear axle RPM and then alters the ratio in a second step from the input pully to the one on the flywheel axle (big gear driving small gear again). I donāt know the specific pulley sizes but they could likely be found or estimated within reason. With a super quick CAD overlay estimation based on a side pic, Iād call the ratio around 6:1 for the Kickr itself.
The final flywheel RPM is the combo of those above.
Main point here is that only looking at the bike gearing misses a huge part of the picture and canāt be used as a single comparison to any other trainer or smart bike, until you include the 2nd half info.
And the other X-factor here is the flywheel itself. Weight is often discussed but it is incomplete info. Two flywheels of equal mass could have very different inertia depending on the physical size and placement of that mass. A small diameter and wide FW will have less inertia that a tall skinny one even if the mass matches. Itās Polar Moment of Inertia that matters here. It could be swagged for these to estimate the deltaās. So any full comparison needs all those details to really understand what each offers relative to the other.
Itās all part of why I think it hasnāt been a topic of discussion beyond the fringe, since it is not a single or simple process to answer the deltaās between in/out or even different trainer options. Some of it can be answered with stuff like spindownās from known RPM & āspeedā values, but even the trainer mode in use may impact those results and must be considered too.
Good points. This is actually an area I wish @dcrainmaker or @GPLama would dig into in detail. Iāve done testing - e.g., VO2 max, lactate - on a Velotron in the past, and the pedaling feel was superior to any of the modern (in my case limited to a Gen1 - maybe Gen 0.5 - Kickr and the SB20) smart trainers Iāve ridden. I wish there was a way to āquantifyā āroad feelā to use as a comparison between trainers in different gear combinations.
I reserve the right to be wrong, not the least of which is a total SWAG on the trainer ratio, but just for funā¦
Missing is the mass & polar moment of inertia from the flywheels, but it paints a picture of the differences that may exist.
There absolutely is, from a pure physics standpoint at least. We just need someone willing to put in the work to find the data and mathify the heck out of it
That data would then need to be applied to an estimated shape/size to get the polar moment of inertia. With that info, itās possible to get a decent guess on the inertia between them.
You mention the Tacx Neo stuff, which is super interesting on itās own. They use actual motor propulsion to simulate the āvirtual flywheelā in their stuff, since the actual flywheel mass is negligible by comparison. Depending on the motor specās, it seems possible (in my simple brain concept) that they could accurately fake an endless set of rider mass and road conditions. I know they do whatever they do based on their own calcs, but like very other trainer maker they donāt really share that externally.
Iāve looked into a similar topic a few years ago when showing the changes in peak power phase when using different gears in ERG mode (same watts, same rpm, PPP changes based on flywheel speed/gearing). It needed the 50Hz Rotor power meter setup using their app (they no longer have?) to demonstrate.
I know the SRM PM9 has some interesting real-time high speed capabilities (iirc 200Hz) that might be useful for this task. That mode isnāt unlocked for standard users or on mine at this point.
