Can this power be realistic?

BugsBunny
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Can this power be realistic?

Postby BugsBunny » Thu Aug 30, 2018 12:49 pm

Hi all

My colleague recently bought a Tacx Neo (I have one too). Last night we rode together in a Zwift race. We had an audio connection as we rode to chat about his Neo and how he was feeling as we were riding. He is about 34 years old and weighs 64kg and 170cm tall. He is new to ergo trainers but has been biking very infrequently for a year or two.

We rode the Innsbruck flat 4 lap race. So about 8.8km per lap with about 72m elevation gain.

What worried me was that at about 55 min into the ride, he was really struggling. Going by my Strava stats, (I weight 63kg), the first 55 min of the ride, I had an avg power of 88 watts. I asked him how he felt on a scale of 1 to 10, he said he was an 8.5 in terms of tiredness. So we said, well just make the hour mark and stop. So I dropped off the line and told him I would just continue on my own and finish the 4 lap race. I realized later he continued also on his own to finish the race.

What I'm thinking is, there might be something wrong with his Neo/setup. I frankly, cannot believe the power numbers as we rode were so low and he was suffering so hard struggling.

From his Strava, I can see one anomaly. It said his max cadence was 176 which doesn't sound right.

Here are the stats:
Distance: 36km
Moving time: 1 hr 34 min
Elevation: 308m
Avg speed: 22.5km
Avg cadence: 80 --- max 172 (seems wrong)
Calories burnt: 445
Weighted avg power: 86 w

Does his power avg sound realistic? Neo setup problem? I ask because when I rode with him a long time ago IRL, he seemed to be able to ride higher numbers than what is indicated.

Bugs

Jmuzz
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Re: Can this power be realistic?

Postby Jmuzz » Thu Aug 30, 2018 1:21 pm

Something has to be wrong unless he is really sick

BugsBunny
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Re: Can this power be realistic?

Postby BugsBunny » Thu Aug 30, 2018 1:50 pm

Thanks Jmuzz.

I might add there was a third person riding together. He too was on a Neo and weight few kg more than me and avg 92 watts over the 55 min. This means that the power readings all seem to sensibly align from the Neos. The only thing that could possibly be skewing it would be his Neo being faulty and causing him to work much harder for the 80 or so watts.

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A_P
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Re: Can this power be realistic?

Postby A_P » Thu Aug 30, 2018 2:00 pm

i dont know how the weighted av power can be as low as 92 watts in the first place?

looking at my PM data, id struggle to do a slow recovery ride with no elevation at less than 175 WAP
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Jubas
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Re: Can this power be realistic?

Postby Jubas » Thu Aug 30, 2018 2:12 pm

It feels like you guys forgot to put a '1' or '2' in front of your power numbers? =/

adam0bmx0
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Re: Can this power be realistic?

Postby adam0bmx0 » Thu Aug 30, 2018 3:17 pm

Yes my first thought too, a weighted avg power of just 86 watts just doesn't sound right in the first place!

RobertL
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Re: Can this power be realistic?

Postby RobertL » Thu Aug 30, 2018 3:46 pm

A weighted average power of ~90 watts is nana toodling to the village shop on her omafiet.

Something seems wrong.
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biker jk
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Re: Can this power be realistic?

Postby biker jk » Thu Aug 30, 2018 4:41 pm

RobertL wrote:A weighted average power of ~90 watts is nana toodling to the village shop on her omafiet.

Something seems wrong.


I used a Power-Speed bike calculator and 22.5kmh avg speed on the flat requires 81 watts at 64kg.

BugsBunny
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Re: Can this power be realistic?

Postby BugsBunny » Thu Aug 30, 2018 5:02 pm

Thanks guys.

I believe there must be only two plausible explanations:

1 - His Neo/installation/Zwift setup/firmware is invalid causing him to exert more watts than what is being reported; or
2 - He is genuinely unfit and/or not used to sustained efforts (for about an hour).

It concerns me because we three have booked a ride together in Japan and we had planned 80km/100km/100km over 3 days. If he is struggling with ~80-90 watts over an hour then I'm lost for ideas as to what pace we should ride at to cover those distances.

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Thoglette
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Re: Can this power be realistic?

Postby Thoglette » Thu Aug 30, 2018 5:17 pm

BugsBunny wrote:1 - His Neo/installation/Zwift setup/firmware is invalid causing him to exert more watts than what is being reported; or
2 - He is genuinely unfit and/or not used to sustained efforts (for about an hour).

3 - His brakes are dragging.
4 - His rear tyre is rubbing on the frame.

I see (ok, do :oops: ) both of these regularly.

A decent once-over of his equipment might be order (the bike, not that equipment) to rule out things like a stuffed wheel bearing.
Stop handing them the stick! - Dave Moulton
"People are worthy of respect, ideas are not." Peter Ellerton, UQ

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A_P
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Re: Can this power be realistic?

Postby A_P » Thu Aug 30, 2018 6:33 pm

isnt a Tacx Neo a wheel off trainer?
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BugsBunny
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Re: Can this power be realistic?

Postby BugsBunny » Thu Aug 30, 2018 6:39 pm

A_P wrote:isnt a Tacx Neo a wheel off trainer?


Yeah... so that rules out the brake rubbing.

I've asked him to update his firmware, buy a HRM and invited him to have a spin on my Neo to see how it feels compared to his.

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Tim
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Re: Can this power be realistic?

Postby Tim » Thu Aug 30, 2018 6:46 pm

Barking up the wrong tree. There's nothing wrong with the equipment.
biker jk has the answer.

ironhanglider
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Re: Can this power be realistic?

Postby ironhanglider » Thu Aug 30, 2018 7:30 pm

What if the software thinks that he is riding at 22 mph rather than km/h?
(I presume that a weight of 64lbs would give a higher number)


Cheers,

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macca33
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Re: Can this power be realistic?

Postby macca33 » Thu Aug 30, 2018 9:20 pm

Perhaps he isn't as fit as you may think?
CAAD10 Berzerker & Focus Mares CX & Ridley Noah SL

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Jmuzz
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Re: Can this power be realistic?

Postby Jmuzz » Thu Aug 30, 2018 10:03 pm

Does weight even come into it on the flat?
Basically just a little extra rolling resistance on the tyres and assume you are bigger with more wind drag.

BugsBunny
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Re: Can this power be realistic?

Postby BugsBunny » Fri Aug 31, 2018 12:09 pm

macca33 wrote:Perhaps he isn't as fit as you may think?


I think this may be the case. Which is not an issue as I understand we all start from a low fitness base. But frankly speaking, this level of fitness was way outside what I thought was reasonable for a youngish gent with his physical attributes.

My reason for posting is to ensure I plan our Japan bike tour well so that our expectations are achievable. I had already decided to ride as a pair with him and slow my pace to suit and enjoy the scenery (I'm riding a Brompton folding bike) and take lots of photos. But now I think I really need to keep a close eye on him if we are to reach our daily destinations/distance goals. Add to that time limits due to riding in daylight hours. It will be 30 degrees in Okinawa so water, rest, pacing, nutrition will make for a testing ride.


Thanks y'all.

Bugs

Jmuzz
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Re: Can this power be realistic?

Postby Jmuzz » Fri Aug 31, 2018 12:24 pm

Tim wrote:Barking up the wrong tree. There's nothing wrong with the equipment.
biker jk has the answer.


The power reading is logical.
But it is likely that it's physical drag is faulty, so it thinks it is applying 85W of resistance but it is really applying 170W or something.
Or it is missing axle revolutions, eg if it has 3 magnet pulses per rev and one fell off so it is reading 2/3rd speed which messes up the power = torque * rpm calculations.

Of course it is possible the guy is just that unfit somehow.

Fairly easily checked with a real world comparison.
Find a flat circuit and do max effort for 5 or 10minutes then compare with trainer max effort for same time.

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Tim
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Re: Can this power be realistic?

Postby Tim » Fri Aug 31, 2018 3:58 pm

I still don't think there is anything wrong with the equipment.
As a comparison, today I did a 50 km easy spin on the relatively flat Zwift London course.
I weigh 61kg's, averaged 25.9 kph with an average power output of 94 watts. This compares closely to the OP's mate, similar body weight, slightly faster and a correspondingly marginally higher output.
You guys are all used to seeing higher wattage figures because you all weigh more and put out higher raw wattage figures.

Newcastle Dave
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Re: Can this power be realistic?

Postby Newcastle Dave » Fri Aug 31, 2018 5:19 pm

At my weight, I have to put out about 200 Watts just to get moving :D

Jmuzz
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Re: Can this power be realistic?

Postby Jmuzz » Fri Aug 31, 2018 5:58 pm

Yeah but he was "8.5/10" tired after about 20km at an "easy spin" 20kph pace.
Which is what Bugs finds odd and raises the questions on whether the trainer is penalizing him with extra resistance.

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Tim
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Re: Can this power be realistic?

Postby Tim » Fri Aug 31, 2018 6:45 pm

Nah, I reckon he's just not very fit.

kenwstr
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Re: Can this power be realistic?

Postby kenwstr » Sat Sep 01, 2018 8:44 am

I think power in a fluid medium is proportional the the cube of the speed.
Aero Drag Force = 1/2 x p x V^2 x S x Cd
and power = Force x velocity
Therefore Force is proportional to V^3 (rolling resistance is very small so ignoring it for simplicity)

I'm 62 Kg and it takes less than 200 W to average 30 kmph
So estimating on that basis and assuming a similar windage area based on weight:

So if say it takes 200W to do 30 kmph

Then at 22.5 kmph, Power = (22.5/30)^3 x 200 = 84.4W

The trainer seems about correct then.

Ken

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kb
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Re: Can this power be realistic?

Postby kb » Sun Sep 02, 2018 1:39 pm

He could just not be used to the lower inertial load. Much easier to take breaks pedalling on the road and keep moving.
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fat and old
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Re: Can this power be realistic?

Postby fat and old » Tue Sep 04, 2018 11:42 am

What KB says. I use a trainer once in a blue moon, and it shows up my lack of fitness really quick. I can ride for hours on the road, but an hour on one of those? forget it.

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