Tire pressure and Dumb Trainer

Question. Why does my cadence stay relatively the same but the power increases as intervals continue?
My set up is a dumb trainer Cyclops fluid trainer with a Sages crank based power meter and Garmin speed and cadence sensor. Tire pressure? Bad form? Bad power meter? I try to make sure I pump tires up once a week to about the same pressure lately but not every ride and not extremely precise. I have been getting more refined in my training and I have noticed that often times during ramp test and other repeating med-long intervals the cadence needed to hit power targets remains pretty similar even thought the power numbers are rising to match target. Really was worrisome on last ramp test since seemed like same cadence resulted in power gains over last half of the ramp test. Makes me question if my power is really accurate if my cadence and gearing is the same but my power is rising.

This is likely multifaceted.

  1. Tire pressure when set cold is one thing. But the tire will gain temperature from the friction and pressure of the tire deforming over the trainer roller. This leads to heat buildup compared to cold start. It likely changes the internal tire pressure AND the performance of the tire itself from the change in tire carcass pliability. No idea the ultimate give and take between the pressure and wall flex, but it is very likely “different” from when you start.

  2. The fluid viscosity of the trainer will experience some changes between cold and normal (hot) operation temps. I don’t care how much a trainer company claims that temps won’t affect the power curve because they are using temp stable fluid… I have seen it change just like you are seeing. Yes, as mentioned in #1, the tire plays a part, but I firmly believe it is only half of the issue, and fluid viscosity shifts during use.

Presumably your power meter is using temperature compensation, so if you do a proper calibration before rolling, it’s practical to assume your power meter data is “good”. I would trust it well above assuming the trainer and your tire aren’t at fault here.

Essentially, having a power meter is great and you need to use it as your guide. That means you will need to shift and use cadence changes to keep power in the target range as your workout progresses. Just one of the compromises of using a standard trainer and gearing to hit various power levels.


As always, I open up a thread and discover that @mcneese.chad has already answered the question. So I just give a like and move on.

This was one of my biggest issues when I was using my Cycleops Fluid 2 and I will agree that it is exceptionally frustrating. I always just came to the same conclusions as Chad mentioned above but it is draining to have to alter the cadence during an interval or see the power off target. I just considered it as a bit more of a “real world” type event because sometimes to maintain the same power outside the cadence does have to change, sure its not as smooth as it is on the trainer but nothing is.

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Sounds similar. I have the Kinetic Road Machine, that they claim has no changes with temp, but I have seen it with multiple bikes and different power meters. So, that kinda rules out the PM as the fault, and points to tires at least being consistently part of the problem or not, since I had different ones along with the different PM’s.

It’s most likely a blend of the issues and I think each contributes at different times in different ways. It may tend to stabilize if your work to recovery is pretty consistent in keeping the entire system “hot”. But I know I saw some reset take place in longer recoveries at lower wattage, only to see the power resistance creep back as I got into the work intervals again.

Kinda frustrating, and means you have to keep an eye on power to fine tune cadence and/or shifting to suit the power targets. But as you say, some people like this level of interaction to keep the workout interesting and it may be “closer” to the general issues we see riding outside, like needing to adjust cadence for changes in road pitch, wind and other influences… if we are shooting to hold a power range at least.