Tacx announced the release of firmware version .34 for Tacx Neo 2 on January 29th, 2020. That firmware update brought a frequently requested update to Neo 2 linearity that made a significant difference at higher flywheel speed.
Neo 2T received an update for linearity in firmware version .31, but there was never a mention of any such update for Neo OG. This left some wondering how the three generations of Neo compare to each other with respect to linearity.
What Is Linearity?
Simply stated, linearity is the ability for the trainer to resist a power target such that the resulting graph is a straight line regardless of flywheel speed. When we’re talking about a power target in this context, we’re specifically talking about erg mode, where a power target is set, and the expectation is that the trainer will “hold” this power target to relieve the rider of this task. This is a stumbling block for all trainers, but some are better at it than others.
Before we began the tests, we performed some maintenance to help remove some variability from our testing.
The Neo OG we selected for our testing was using an Edco branded freehub, while the Neo 2 was using a Tacx Shimano freehub that came with the unit.
For both Neo and Neo 2, we removed the existing freehub and simple bearing, cleaned the axle, and replaced the freehub with a brand new Tacx Shimano freehub. The freehub was shared between them so we were testing the same freehub and cassette. The freehub, axle, and simple bearing were greased with Park Tool Polylube PPL-1.
We installed brand new Shimano Ultegra 6700 10 speed 11-28 cassettes on both the Neo/2 freehub and the Neo 2T. The cog sizes for this cassette are 11, 12, 13, 14, 15, 17, 19, 21, 24, 28. Both were torqued to 40Nm with a Norbar 130101 torque wrench.
|Firmware Version||0.7.4 / 0.8.4|
For all tests, we concurrently recorded power from Favero Assioma Duo. Both pedals were running firmware version 04.25
Initially, at and when switching between trainers, the pedals were zero offset with the crank arms in vertical position.
For all tests, we used Garmin Edge 520 cycling computers. Both were using version 13.00 software.
One of the 520 computers was dedicated to recording the cadence and power from the Assioma power meter via ANT+.
The other was updated for each trainer to record ANT+ Power from the Neo unit currently being tested, and cadence data over ANT+ from a dedicated RideSense magnetic Speed/Cadence sensor connected to the bike.
For these tests, we decided to use Zwift on MacOS because it has a very simple workout creator interface that can be done within the app, and also allows us to test other trainers outside of the Tacx ecosystem. While we are focusing on the Neo family of trainers, we will (in upcoming tests) show that the same phenomenon exists across all trainers, including Kickr 2018 and Saris H3.
The workout consisted of a single 120 minute interval at 100%. We artificially set our FTP to 100 watts to give us a consistent 100w workout. The cadence reminder was set to 90 rpm.
The Power Source and Controllable Trainer settings were connected via Bluetooth to the Neo unit being tested. The Cadence setting was connected via Bluetooth to the RideSense dedicated cadence sensor.
We used a dedicated trainer bicycle, a Giant TCR Advanced SL0 Di2 10 Speed 50/34.
Before the tests, we cleaned the derailleur cage and replaced the jockey wheels with new Tacx Shimano 11T Standard pulleys and Shimano OEM screws.
We also replaced the chain with a new Shimano 6701 10 speed chain and connected the ends with YBN QRS10 link.
The chain was lubricated with NFS using the 12:12:12 method. We deliberately added a drop of NFS to the QRS10 link.
This unit has an updated RideSense speed/cadence sensor with ANT+ / Bluetooth capability that was used to transmit cadence via Bluetooth to Zwift, and ANT+ to the Garmin Edge 520.
Intervals were tracked with a Gymboss interval timer set to 1:00.
- Start the interval tracker. During the first minute, engaged Zwift erg mode for the first minute and ramp up to 90 rpm cadence.
- At the interval signal, both Garmin Edge computers were started at the same moment.
- The bike was pedalled continuously at 90 rpm as closely as possible.
- At each additional interval signal, the derailleur was shifted outboard by one cog, consecutively, until each cog had been recorded for exactly one minute.
- The “garbage minute” occurs in the middle of each recording where the derailleur was shifted back to the largest rear cog and the front chain ring was switched to the large ring. The cadence and watts were intentionally dropped to zero to help scaling issues in the output graph, and then pedaling resumed to re-engage erg mode in Zwift.
- The previous steps 3 & 4 were repeated whilst pedaling in the large chain ring.
- Both cycling computers were stopped when all cogs had been recorded for exactly one minute.
Note: because the 28T cog has the benefit of not being shifted into during data collection, it doesn’t have the “shift bump” power spike that all other cogs have. This could be equalized in a future test result by running the cogs from smallest to largest.
How To Read The Graphs
Each test began at a certain “second” in time, so to find any complete value, select from the initial minute:second, and select to the next minute:second.
Neo OG: 47
Neo 2: 13
Neo 2T: 21
Each graph starts in the small chain ring and largest cog, so left to right, there are 10 minutes of small chain ring. Then there is the “garbage minute” which has been excluded from our results. Then there are 10 more minutes of large chain ring. Any extra data at the trailing end beyond the 1 minute mark has been excluded from our results.
There were no surprises in store here. Neo OG has been known to have this defect for quite a long time, and the results are consistent with expectations.
The average difference was 4.06%, with the closest fidelity at 0.21% in the 21T cog and 34T chainring.
The worst fidelity was a whopping 31.36% in the 50T chainring and 11T cog.
While the trend lines for these graphs may appear similar, don’t let that fool you. You have to consider the scale as well. In the small chain ring, the largest difference was 13 watts. In the large chain ring, the largest difference was 34 watts.
While it’s interesting to see how the Neo tracked compared to the power meter, the really important metric — and the thing we cared about in the first place — was how closely the Neo and power meter tracked to the initial target of 100 watts. That’s going to tell a similar story, but when you see in expressed in watts, you get a different appreciation for what’s really happening.
When you look at the Distance From Target graph, you can see right away that Neo is clearly underreporting, since the watts from Neo are very close to the target, but the watts from the power meter are stratospheric.
This was our second effort with the Neo 2, the previous having come the day after the .34 firmware was released. The result is very similar to the first, though not exact, which makes sense because we made changes to the testing apparatus.
The average difference was 3.76%, slightly better than Neo OG. The best fidelity was 0.15% in the 19T cog and 34T chainring.
The worst fidelity was 24.47% in the 50T chainring and 11T cog.
Looking at the target fidelity, the Neo 2 definitely does have some improvements, holding very near to the target and the power meter in the small chain ring through the middle of the cassette, but again, the Neo underreports its value.
Here again, we see the issue in terms of watts, where Neo reports a value below 7 watts at its maximum distance from target while the power meter climbed up to nearly 31 watts. While this is still a vast improvement over the original Neo 2 with pre-.34 firmware, it’s only slightly better than Neo OG. In fact, in the small chain ring, it’s actually a little worse, as we’ll see shortly.
The Neo 2T we tested was still using .31 version of firmware, which includes the original linearity fix. The firmware updates in .32 and .34 do not affect the outcome of this test (or shouldn’t!) so we did not update the Neo 2T before testing.
While the minimum difference between Neo 2T and the Assioma pedals was very similar to both the Neo 2, that is where the similarities end. In the small chain ring, the closest fidelity was 0.67% in the 17T cog and 34T chainring, but the average difference was a mere 0.24%! That is because for some portion of the time, Assioma read lower that Neo 2T, netting a very low average. Why that happened, and to this extent, is not yet understood. Even so, the maximum difference was 3.04% which is dramatically different from OG or Neo 2 — and that was in the small chain ring!
The result from the small chainring was so surprising that we’re going to have to run it again or a few times. There’s nothing to say that it can’t be like this, but it’s definitely not what we were expecting.
Moving on to the large chain ring, we see another round of differences between how the Neo 2T behaves compared to Neo OG or Neo 2. The values in the large chain ring tracked so closely that you can barely see daylight between the digits. That’s not because Neo 2T was significantly better at holding the requested resistance (it wasn’t); the highest average value reported by Neo 2T was 126.6, just a small step behind Neo 2 at 130.8.
The difference is that Neo 2T reported the output more realistically., creating a situation where the average watts reported by Neo 2T was higher than the average watts reported by either OG or Neo 2. In essence, Neo 2T is simply more truthful about its inability to resist low watts at high flywheel speeds, reporting the watts more faithfully than Neo OG or Neo 2.
On paper, that may cause fidelity to appear more reasonable with Neo 2T, and while the values were definitely lower, the behavior is effectively the same as with Neo OG and Neo 2. The grass is not that much greener.
When we look at Neo 2T from the Distance From Target perspective, you get a very keen idea why I said initially that Neo 2T really shined. While I feel that Neo 2T slightly over reported watts with Neo 2T, the fidelity to the target was such that the training impact of such differences would be very difficult to measure. This is a very, very nice result in the 34T chainring
Where Neo 2T really loses linearity at higher flywheel speeds in the 50T chainring, it at least maintains credibility by reporting watts much nearer to what our power meter was reporting. The actual watts themselves were closer to the target as well, so overall.
To really get an appreciation for just how good Neo 2T is, you have to see the trend lines in watts between all of the trainers side by side. In the 34T Chainring, Neo 2T is far and away the most linear. When you examine the trend lines and notice that the Neo 2T is the only one that’s even close to horizontal, there is a very clear leader.
When it comes to the big chainring, though, Neo 2T has its achilles heel nicked. Although the numbers are lower overall than Neo OG or Neo 2, the trend is still similar. In this case, Neo 2 and Neo OG again reverse roles, with Neo 2 edging out the Neo OG, and the Neo 2T edging out both. In the big chain ring, linearity is just an issue that will probably not be resolved any time soon.
If you’re going to use erg mode for your power based workouts, we still recommend using the small chain ring and a straight chain line, mid cassette, and occasionally vary the rear cog to distribute the wear more evenly.
Start in the 21T cog and conduct your workout. Next workout, shift to the 19T cog. The next workout, shift to the 17T cog. Then go back to the 21T cog and repeat for subsequent workouts.
This will keep your watts in a reasonable range while adding longevity to your indoor drivetrain.