I just did a ramp test on TR. Test was performed on my wahoo kickr snap trainer using my stages power meter in ERG mode. Everything felt fine during the test, such as it got harder and harder each minute until failure. However, my power in the last 2 minutes diverges from the prescribed power line significantly (see screenshot) even though i was in ERG mode. I didn’t notice this during the test as my eyes were too crossed at this time to notice. If i didn’t see this divergence on the screen i would of said power increased each of the last 2 minutes as i could feel the increase in work required to keep things moving forward.
What would cause this when I was in ERG mode? I realized i am biased, but my view is the power was off. My FTP has been in the range of 245-250 for the past year. right now i am in the best shape i have been in during that period throwing down personal bests for power. Ramp test result is a -10W decrease in FTP. doesn’t add up. my HR continued to increase in the last 2 minutes suggesting workload (power) was increasing and i noted it was harder and harder to pedal as i felt the resistance increase in each of the final two minutes… I’ll put a ticket in with tech, but figured others may have seen this happen before. If i completed the last workload as prescribed y FTP would have been about 260W vs the 236 W it said it was. again based on my history with FTP in this range i would say the 260 is correct. stinks to have doubts after putting in a max effort and preparing for days to take the test. would like to not have to repeat to prove it right/wrong as it messes with training a fair amount. I know FTP isn’t everything but after a lot of hard work it is nice to quantifiably see an improvement in performance metrics.
The cadence drop off appears accurate as I tend to have to grind out the last few stages of a ramp test. I just can’t maintain RPM even though i tend to be a spinner at lower workloads (95-100 rpm). Was about 60-62 rpm near the end and I would say this is right on.
I had a similar problem on my old trainer (cheap old one). The resistance of the trainer was not strong enough for the highest powers in the lower gears.
At each step of the ramp, the trainer increases the resistance. When the trainer reach its maximum, the difficulty does not increase anymore even if the program asks it to. Coupled with the lower cadence it can lead to even lower power.
The trick to solve my problem was to use a gear high enough, making the wheel spin faster. The max power the trainer can manage is “max resistance x wheel speed”
Looks to me you were just getting dragged into the spiral of death, resistance is going up, your working harder but your cadence is falling so your effective power is falling. For the majority of folk the ramp test is great as there’s not massive TSS incurred but for some folk they either test too high or too low. Its a bell curve statistic. Its a long time since I’ve done a ramp test but I found they tested progressively lower for me, so I was using 20mins tests in the off season but they do incur big TSS; laterally however, I’m using AI FTP. AIFTP has always detected 20-40w above what I got on my last ramp test and is in line with my 20mins tests.
Separate from the trainer/TR issue, I’d be interested in what @The_Cog thinks about whether a 60ish cadence at the end of a ramp test skews the results.
‘Ramp’ (incremental) tests aren’t a very precise way of estimating FTP in the first place.
Dropping your cadence will, to a point, allow you to generate more power (as muscle fatigue is associated with a decrease in shortening velocity, such that a lower cadence is more efficient). Within limits (and 60 rpm would be too slow for most), that would help you eke out a few additional watts versus continuing to pedal at the same cadence, and hence lead to a higher estimated FTP. However, I have never used a so-called smart trainer, so don’t know how it might impact the reported/actual power.
Regardless, with any trainer you should use the largest gear ratio you can get away with, as that will maximize the inertial load, and therefore best replicate cycling outdoors (although none really come close). Only reasons to shift to a smaller gear are 1) too much friction/grinding in the smallest cog (10 tooth cogs are just plain stupid…even 11 tooth cogs suck), or 2) your trainer can’t handle the higher wheel speed.
I haven’t done the math, but I would say probably all.
For example, my ancient Velodyne trainer has a 10 kg flywheel spinning at hundreds of rpm, and it has only about 1/3rd the inertial load of cycling outdoors on a level road at the same “speed”. No modern wheel-off trainer comes close.
To appreciate the difference, try doing a seated maximal acceleration from a dead stop in the same gear on a trainer vs. outdoors. You will “get on top of the gear/spin out” much more quickly on any trainer, reflecting the lower inertial load. This difference also exists/impacts what happens within a single pedal stroke even at a steady cadence, and impacts the physiological requirements and presumably the resultant adaptations. Using smaller gears just makes matters worse (at least if your goal is to be able to ride a bike fast, vs. be good at virtual cycling, e.g., Zwift).
I was more thinking about typical MTB pedalling at high RPM but very low speeds and therefore low inertia (Comparatively to even lower speeds on road).
Another vote for some combination of inertial load/maxing out the trainer AND cadence/power death spiral. IME, the test will let you reduce cadence and power like you encountered - the test won’t stop until you quit pedaling. As soon as your power drops like that, you may as well stop - no further effort is going to increase the FTP estimate unless you can get the power back up. Of course, if you don’t notice the power drop, … not much to be done about that.
Okay, but when I started on a wheel off trainer, I was told to never use the big ring. Something about the inertia and intervals. Yes the noise on the H2 was definitely louder in TBR. On a smart bike it doesn’t seem to be an issue as it chooses the ‘right gearing’ in ERG mode, and usually is always in TBR, but I don’t see where that matters as much (again, in ERG mode).
But yes, I was told by many people to never ride the trainer in TBR. I always did, and tried the small ring and didn’t like it. I thought the idea was the inertia would smooth out shorter interval demand. The physical flywheel did take noticeably more time to slow down.
These smart bikes are a different use case than a bike & trainer combo. Smart bikes all use a single, fixed drive ratio with a single front belt pulley (large-ish) and a single rear belt pulley (small-ish). This makes them spin the flywheel at a higher ratio, on par with a big ring bike & trainer setup.
Despite the “gearing” options these smart bikes employ, those are ‘fake’ gears that don’t actually change the flywheel speed. Those gearing systems simply manipulate the resistance unit braking action to alter the feel.
No matter what “gear” you have selected, 90 rpm at the pedals will yield the same flywheel speed. So these are an exception when discussion ERG and “gearing” compared to a regular bike & trainer combo.
