Hermes

I found this video that discusses why it seems harder, for most people, to make power on a trainer versus riding on the road. For me, it seems significant. Based upon the force I feel in the bottom of my feet, my 30 second power is 150 watts less on the trainer compared to the road and my steady state power about 30 watts. I have tested the watts measured by the smart trainer against my SRM and the smart trainer is accurate.

On today's workout on Zwift on the Kickr, I tried to pulse the power in versus a smooth spin. As one data point, the level of effort for a given power seemed to improve albeit still harder on the trainer.

What is your take on this and is there anything you do to mitigate the effect, if any?

PeteHski

I guess I must be one of the lucky ones he mentioned at the end of the video. With the notable exception of full-on OOS sprints, my indoor and outdoor power is much the same. I’m using a Kickr Bike, which does have a motorised virtual flywheel which makes the pedal inertia feel pretty realistic. I also use a decent fan on full blast when riding hard. I also ride more indoors than outdoors, so that could be a factor too.

Trakhak

The answer seems obvious: it's the miracle of planing (when outdoors, riding your steel sport touring bike, naturally).

My real guess: might have something to do with the way we tilt the bike from side to side when pushing hard, presumably maximizing the efficiency of power transfer. Trainers don't allow that to happen, obviously.

Still, 150 watts seems a surprisingly large difference.

No idea how to solve the problem. Maybe check the relevant forums for the smart trainer and Zwift for similar complaints and solutions.

terrymorse 

I have no idea why, but my heart rate is consistently at least 10 beats higher on the trainer, and my perceived effort is higher.

I doubt it's about heat removal, as I keep the room cold and use a powerful fan. Those extra heartbeats are doing something, aren't they?

RChung

What does your QA (that is, pedal force-pedal speed or cadence/crank torque) plot look like on the trainer vs. on the road for "similar" types of ride profiles? And, not so visible on the QA plot unless you zoom in, what do they look like during sprints and accelerations?

[Edited to add:] My outdoor sprint power is hugely higher than my indoor sprint. My outdoor hour power is a little higher than my indoor power, but at lower RPE. When I look at my QA plot, they seem different, and especially when I examine fast accelerations.

Sierra_rider

I guess I'm not the only one then. I'll admit that the smart trainer is considerably easier at the same % of FTP, than my old dumb trainer was with the power meter on the bike. That being said, I still just can't get the same numbers on the trainer as I can out on the road. The disparity does come down as I use the trainer more, but never quite goes away.


IMO there are 2 things that help me get increased power off the trainer. The first is just the undulation of the road. I don't really like riding at a steady power number, my power varies frequently by 20 watts or more on climbs. The second, is that I can just mentally push harder on a climb...especially on extremely steep climbs. My best 20 minute power usually comes on steep hills that I'm having to ride at my "limit" just to keep a comfortable cadence. Even when doing FTP tests on the trainer, I'll pick a Zwift climb to do it on, just because I get a slight emotional boost from it.

Ric Stern

FWIW, i find it's an adaptation process. My training goes like this:
spring 50:50 indoors/outdoors
summer tails right off indoors and is all mainly outdoors
autumn 50:50
winter 95:5 (indoors/outdoor)

during spring and winter i find my indoors and outdoor power exactly the same (and in some instances, perhaps even higher indoors - maybe i'm not worrying about traffic or potholes). at the start of autumn i suck badly indoors, power and duration is significantly lower than i can normally maintain, which normalises by winter (or about 6 weeks after i start regularly riding the indoor trainer).

some evidence suggests that there's differences in the way we pedal between indoors and outdoors - (it's been a good while since i looked at it, but it came from Canterbury Christ Church College, and the team led by Richard Davison - although he's since left and moved. But also Damian Coleman).

PeteHski

This makes sense. I do most of my training indoors on a Kickr Bike, so I guess I’m pretty well adapted to riding that trainer. I also think it does a pretty good job of replicating my outdoor pedal stroke. Subjectively at least, it feels much the same to me on climbs, flats and descents.

Interestingly I do find it considerably harder to average the same power in ERG mode vs free riding in sim mode. Holding a constant power level in ERG mode just grinds me down, both physically and mentally, even at relatively modest power. But I find this effect varies between different trainers. My Kickr Bike is quite forgiving in ERG mode, allowing for slight power variations around the target value without feeling too artificially restrictive. Some trainers feel really harsh and unnatural in ERG mode. For this reason I only use ERG mode for short, variable intervals, 5 mins max at constant power. Long endurance or sweet spot intervals in ERG mode are my idea of a slow and painful death!

Ric Stern

i'd avoid erg and workout mode like the plague....

Jughed

Could it have something to do with your build/strength? Larger/stronger riders may not need to rock the bike as much or use their upper body as much to generate power?

I find it easier to put down power and do intervals on the trainer, and I see some of my best numbers... I tend to have more muscle soreness/fatigue after an outdoor ride.

I do train in a cool 62-64 deg basement with a big box fan, so heat isn't an issue.

PeteHski

I only use ERG mode with Sufferfest/SYSTM workouts, but they tend to be pretty fluid with their power targets. But I could never stand doing longer Z2 and Z3 sessions in ERG mode. There was one session with 3x20 min constant power intervals that I hated.

I’m currently just free riding in Zwift as a proxy for my outdoor riding. I find that more productive for longer sessions and certainly feels more natural. When I want intensity I join a tough group ride or race. Also plenty of virtual hills and mountains to work on. The Kickr Bike proved to be a good investment for me. I actually enjoy indoor riding now, where it was previously a chore I avoided.

Hermes

My HR is lower on the trainer and has been that way since I started racing in 2006. I use a fan and the room is cool. At that time, I did not have a power meter so I could not make any power comparisons between the road and trainer.

Hermes

I will post a couple of graphs later.

RChung

I think the most helpful would be if you looked at, say, your best 30 seconds and the preceding 15 seconds (so, 45 seconds total) for both your best ooutdoor and your best indoor efforts. If you're like me, those 45 seconds will look different indoors and out, and the preceding 15 seconds will show the acceleration of how you got there.

Hermes

Getting data is doable but not so easy. For example, my best 2023, 30 second power was 474 watts outdoors climbing a 5% grade on my road bike. That effort was part of a structured 4x 40 second set max power climbing efforts. The effort was sub-maximal. Why? I was on the road and needed some ATP left so that I did not fall off the bike or veer into traffic being too hypoxic. On the track during a 500 meter time trial with a standing start, my 30 second power is 730 watts. How am I at the end of 500 meters? Totally gassed but winding down on the track gasping for air.

On the trainer / smart trainer is it possible to do max efforts and collapse on the bike during a recovery period - no traffic no wind down on the track. So my teammates and I see value in max efforts / intervals on the trainer for deepening ones matchbook and getting stronger. The important point is the hypoxia and effort in ones legs not what the power meter says per se. I am mostly whining about racing on Zwift where all that matters is power/weight over time and I take the point that a smart trainer has a strength and adaptation period.

Having said all that, the only graphs that I have are force versus cadence. I do not see much info in those graphs other than more power equals more force. I know that finding info in seemingly random data is your specialty. Is there another graph that I should try to find. Or do I need different software?

Hermes

My goal for starting the thread was to have a topic to discuss that was relevant to those who ride events outside and inside and their observations and quantitative results. Hopefully, more interesting that throwing San Millan, Coggan or Seiler under the bus.

RChung

If you're doing max efforts on the track and on the trainer (but not on the road) then I'd like to see the data for the track and the trainer. We know how force and cadence combine to produce power -- I'm interested in seeing whether the path through which you get to higher power differs on the track and the trainer (we know they end up in different spots so I'm not that interested in that part; I'm more interested in what leads up to those different end points).

[Edited to add] I've been calling these "power expansion paths." My PEP on the road and on my trainer are quite different.

RChung

There clearly are differences in how different trainers with different inertial loads benefit or disadvantage racers in Zwift. I'm actually also seeking out data files right now for riders who've used both a "conventional" cassette trainer and one of the new "One" virtual shifting trainers on the same routes to see if they shift differently.

Hermes

Okay. I have a lot of data from the track, road and trainer including smart trainer and Kreitler rollers with a Kreitler wind load. For me, the roller setup gets very close to the road with respect to level of effort for watts produced.

And I have a lot of max power data riding a TT bike on the road and on the smart trainer. And some riders cannot make as much power on the TT bike as they do on the road bike. Compiling the data, taking screen shots and posting graphs is tedious. And I have never met an academic that did not want to see the maximum data possible. Are you interested in Force v cadence? That is all I have.

Thinking about the rollers v smart trainer. IMO, it may be the size and inertia of the flywheel that matters. Maybe for me, the Kickr and Tacx flywheel is the wrong size. For someone else, it matches perfectly. Very little flywheel effort seems good for me but others may struggle. Just guessing.

Hermes

500 meter best effort 745 watts for 30 second. PM Garmin Vector 2. Data includes warmup and idle time over a couple of hours until the race occurred.

RChung

Do you know me or what?

Can you send me a couple of .fit files? Maybe "typical" max efforts for the track and the trainer -- and, thinking about it, from the road where you're climbing that hill.

Hermes

Send me a PM with email and I will send you the files.

work4bike

I don't know the answer to this question, because it's funny that I've been cycling since the mid-80's, but have very little time on indoor cycling.

However, I have commented before on road running vs treadmill running and it's a big issue (very controversial) in the running world. Some people think it's harder to run on a treadmill others think the road.

Personally, I don't think they compare much. On a treadmill you're not using as much muscle power to propel yourself; however, your legs seem to turnover quicker (for a given speed of running), so treadmill running seems to me to be more cardio less muscle fatigue, unless you elevate the treadmill.

And there are other factors to include, but bottom line, I don't attempt to compare my runs on the treadmill with my runs on the road and my trail running is also separate from both the treadmill and road running.




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Hermes

Running road v running treadmill. My wife and I feel the treadmill is harder but like indoor trainers there is a strength and adaption period. The question is if one does an indoor activity versus the road are they better off, worse off or the same. My opinion is the time in the saddle or feet on the ground is what matters the most.

work4bike

You're absolutely right. Here's a 5-minute video that encapsulates that sentiment perfectly and you may even tear up a little.