Stages Gen 3 vs Tacx Neo waaaay off

[nickf]

I did my first FTP test this morning. Buddy of mine uses a Tacx neo smart trainer. We did the zwift readout with the Tacx power on the screen. Stages was running on my Garmin 1030. The Stages was 40-50w higher the entire time. FTP Tacx was 245w, Stages for the same 20min was 308w. I did a zero calibration before the start of the ride on the stages. The Tacx nothing, just started the warmup/test. From what I have seen there might be a couple of watts discrepancy but 40+? My stages is only a couple of weeks old. I'm not so much concerned about the FTP number, I have no ego to feed but I feel one or the other was off. Which number do I build workouts on? I'm thinking I should follow the Stages numbers since that's what I own and thats what I will be using with a dumb trainer, when I pick one up. Maybe redo the FTP test with my trainer and the numbers off my stages?

[jlok]

Yes, test your Stage 308w FTP on Tacx.

[spdntrxi]

left / right leg discrepencies...
crankarm vs flywheel..

[AJS914]

Maybe redo the FTP test with my trainer and the numbers off my stages?

I'd definitely compare with your trainer. Since the Stages is only 2 weeks old I'd want to know that it was working perfectly and if not, then I'd send it back.

[TobinHatesYou]

left / right leg discrepencies...
crankarm vs flywheel..

This isn't it. A geared drivetrain is like 97-98% efficient under optimal conditions. If you look at Lama, Ray, Tariq or anyone else's Tacx Neo reviews, they are always within a couple watts average of the "known good" power source. It could be a very heavy L/R imbalance, but that means his split is 154W/91W which is 63%/37%... I've never seen an imbalance like that from an able-bodied person.

It's quite possible BOTH power sources are off because I have heard of more recent Neos being miscalibrated out of the factory. He really needs a third power source in the mix.

[glepore]

The trainer wasn’t calibrated? And you’re wondering?


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[TobinHatesYou]

The trainer wasn’t calibrated? And you’re wondering?

Tacx Neos don't require or even have a spindown operation.

[nickf]

Like others started the tacx is set and forget, that's what I have been reading. But others say warm up 15 min or so and calibrate the tacx. Who knows. I have nothing else to compare my stages to. I'm going to try and see if I can find someone with a kicker to compare it to.

I was thinking a leg imbalance but it would be pretty extreme to be that far off.

I'm going to contact stages to see what they have to say. Opened up a can of worms. Losing interest in the power meter game already.

[TobinHatesYou]

Like others started the tacx is set and forget, that's what I have been reading. But others say warm up 15 min or so and calibrate the tacx. Who knows. I have nothing else to compare my stages to. I'm going to try and see if I can find someone with a kicker to compare it to.

I was thinking a leg imbalance but it would be pretty extreme to be that far off.

I'm going to contact stages to see what they have to say. Opened up a can of worms. Losing interest in the power meter game already.

The Neo[2[T]] and Neo Bike are the only Tacx trainers that don't need spindowns. The Flux models should be given a spindown every few weeks and the wheel-on Tacx trainers like the Vortex need them 15min into every ride (and they still won't be accurate.)

[KCookie]

I have a Kickr and was experiencing the same problem.The watt output just seemed to be way to low so I bought a 4iiii PM and straight away noticed a 40w difference. I would say the trainers are quite a bit out.

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[TobinHatesYou]

I have a Kickr and was experiencing the same problem.The watt output just seemed to be way to low so I bought a 4iiii PM and straight away noticed a 40w difference. I would say the trainers are quite a bit out.

You have no benchmark with which to make this claim, so maybe don't?

[eins4eins]

accuracy is a difficult topic and making assumptions based on comparing two different, uncalibrated systems, isn't really going to tell you anything.

[nickf]

I wish I had the data from the Tacx but I do not. This is the 20min segment done for the FTP Stages Gen 3, Bontrager heart rate strap. Take it easy on me this is my first go at this. With the Tacx it recorded my FTP test at 240w but with the HR numbers recorded below on my Garmin.



Then comparing data from my regular early morning group ride. Yes, it's a group but power is power and heart rate is heart rate. That's my thinking but please correct me if I'm wrong. Lower average watts but my HR is much lower as well. This was a pretty easy ride also just a tempo pace. Laps 2, 3 are nearly identical, with no stops. That's about 20 minutes of solid riding. Lap 4 is the same but we turn off before the lap start point so the time is off a bit. So with my average HR of 125 and average watts at 271 for 20 min, really even longer if I include lap 4. Is that an unusually high watt output for the work? I'm 5'10" 173ish lbs. Just looking down doing a 30second average at 240watts is just cruising at around 21-22mph, I can do that for well over 20 min with my HR around 135-140. I know indoor numbers will differ from outdoor. But by how much? I'm new to all this just trying to figure out what the discrepancy is. Also how many watts is considered "easy" or "hard" everyone will have a different number so that's hard to compute.

[spdntrxi]

The trainer wasn’t calibrated? And you’re wondering?

Tacx Neos don't require or even have a spindown operation.

yep.. no user function for this.

it's been awhile since I've done it on my Neo (2016 ver) basically a 1. Neo is gererally lower by 10w compared to Vector2, Vector3, Stages1. Have not tested my stages2 or stages3 and probably never will get around to it.

[cdncyclist]

I don't have an answer to the accuracy between the 2 devices issue.

But as for training, you have 2 values from 2 devices. If you always have your bike with Stages on the Tacx (and obviously always use your stages on the road) it would make sense to use this to derive training zones. A more confusing way would be to have 2 sets of zones. So I agree with your initial approach you suggested.

Arguably it doesn't matter which is the 'gold standard' (i.e. accurate) as long it is what you are using for both testing and training (and hopefully whatever device you end up using, regardless of if it is accurate or not, at least is consistent - this is likely the most important factor for training with power).