Fluid Trainer vs Kickr - resistance question

First post, hoping I can get some advice.

I have an old cycleops fluid wheel-on trainer, and a left knee replacement. All spring, summer, and fall, I have no issues riding outside (no fit issues), but when on the trainer indoors, even a 15 minute low intensity spin on the trainer will irritate my knee.

I’m assuming that there’s something to do with how the fluid trainer provides resistance during the pedal stroke that isn’t similar to riding outdoors.

I’m considering trying a kickr, kickr core, or kickr roller, in the hope that either a direct drive or the roller will have a more realistic resistance and eliminate the irritation.

Thoughts? Recommendation on which one to try, if any? Unfortunately, borrowing one is not an option as I’m quite remote.

Fluid trainers provide a consistent amount of resistance around the pedal stroke, and that resistance ramps up rapidly as speed/inertia increases. There is less inertia on most indoor trainers, which means that dead spots in your power stroke that you might have due to an injury become noticeable. A wheel off trainer in your biggest gear, say 50:11 might be better, but Erg mode is slower to respond with big gears and high inertia.

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My guess is that you probably need to induced some motion into your indoor setup - like the new Kickr Move. Personally, I’d get a Kickr core and an inside ride e-flex setup.

Thanks Jon, that makes sense. Would you say that there would be less inertia/better approximation of outdoor resistance on the kickr/core than the rollr?

Definitely love the idea of making a setup as realistic as possible. I’ve done some reading on this site, and some of the rocker plate setups are truly amazing.

That said, considering how quickly the discomfort comes on vs outdoor, I’m thinking the resistance in the pedal stroke is the first thing to confirm that I’m compatible with the trainer, if that makes sense.

I don’t know that one or the other is better, regarding direct drive vs. roller. You’re going to get 20 different opinions. Here’s the deal with the smart trainers, and I’d guess the smart rollers too? You get a choice of several modes: resistance, “standard”, and erg. So you can create a good feel situation for the type of ride you are doing. I do a lot of my higher power intervals in “Standard” mode which gives a similar ride feel to a fluid trainer - resistance increases as flywheel speed increases, so it makes it so you don’t have to shift or hunt nearly as much when doing short/shorts or even VO2 intervals.

Resistance mode I’ve found is great for threshold/SST/tempo and even endurance riding. Erg is erg… I use it sometimes, other times not so much.

So you get options with any of the direct drive. I have had a Kickr Core, Kickr 2018, and now a Saris Hammer H3. The Kickr 2018 and Hammer both have superior “road feel” to the Core, IMO, likely due to heavier flywheels. I have no experience smart rollers, so can’t comment… but IMO there is a difference in “road feel” between the mid-level and higher level direct drive trainers.


Kurt- that’s great info, thanks very much. I had no idea there were different resistance mode settings to choose from.

Just to chime in: I had a fluid direct drive dumb trainer (an Elite Volano) for 3–4 years and was very happy with it. I only replaced it once one of the bearings went.

I have an Elite Suito now. I don’t like erg mode for anything but endurance rides. For hard workouts (sweet spot and above), I find erg mode interferes with my ability to focus on hitting my power targets. I use resistance mode for those workouts. What I really like is that by dialing the resistance, I can shift the gears I will be in when I am doing threshold or VO2max relatively well. This cuts down on noise (as I can be in lower gears) and allows me to not be caught between gears.

I would suggest it’s a fit issue, as opposed to an issue with the type of trainer. Sitting on a trainer locks you into a certain position, as you don’t get up as often and the bike doesn’t move around under you. The posters above did suggest getting some movement in your setup, which I think would help, but having it come on so quickly makes me think there is a fundamental fit issue not being addressed, which only presents itself when you are locked into that fixed position.

I had a similar issue, and after a bike fit, and some further adjustments, the knee pain went away.

I just can’t buy that the type of resistance is the key to your comfort.

One thing that I used to do on my trainer was jack the front end up a bit with a riser block. After I got a Kickr, I figured out that I could just put it on the 24" rear wheel setting which gives one a little more upright posture.

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