zpower too high, why?

(Jeff Bricker) #1

I am using the following setup:

  • Cycleops Fluid2 trainer with approximately 200 “miles” of use.  The knob is tightened two full turns after the roller contacts the tire.  I bought this trainer new and there has never been any indication of a fluid leak.
  • Continental Hometrainer 700x23 tire inflated to 100 psi
  • Garmin ANT+ dongle, HR strap and speed/cadence sensor
  • Set up in garage, temperature between 35F and 40F

My zpower is incorrect.  Zwift is reporting FTP around 370W, and this morning I averaged 134 bpm heart rate and 360 W over an hour.  I would not expect to see these power numbers from a 48 year old guy who maybe rides 3,000 road miles a year.

I think I’m set up properly.  I’m using a supported trainer and selected it from the menu in Zwift, my tire pressure and roller tension is correct, and I don’t have trouble with the ANT signal dropping out.

Is there something wrong with my particular trainer?  Could the relatively low temperature in my garage prevent the fluid clutch from ever producing the expected resistance?


(Jeff Bricker) #2

Oh yeah, and my profile weight is correct also.

(Mike Grau) #3

I’m having the exact same problem with my Cyclops Fluid2 trainer and Garmin ANT+ sensors. My speeds are averaging over 16mph per ride, whereas in real life I’m usually more around 13mph. I too am set up in a garage that stays cold until I turn the heater on, where it gets up to the mid 60s F during my Zwift rides. I’d love to get my numbers in line with what I expect.

(David Zimmerman) #4

I have the same issue, too.  zPower is too high.  I train out of my garage, have Cyclops Fluid2 trainer (new as of November) and use Garmin ANT+ sensors.  My real FTP is closer to 170 - 180, not the 262 calculated by zPower.  I plan to use a friends power meter to compare the differences, but that won’t be until next week or so.  

(Mark Boon) #5

I am too -I’ve sent a ticket to Zwift


Cyleops fluid 2 bought this christmas  , designated tyre ,correct weight , garmin speed and cadence and heart rate monitor, garmin ant + 

I’m 50 ,reasonably fit and do 13mph average around the peak district and 15-16 mph on the flat .On zwift I:m tearing past people getting king of the mountain yesterday for a time , reached 300 watts with over 20 mph ave -can’t be correct  - my real life cycling mates can:t compete and I have two who have set up s that seem to be close to real like speeds

can’t decide if it is the trainer or zwift - I’d send a ticket too

I:ve copied this post to them

(John Foote) #6

Was there a resolution to this problem?  I’m having the same problem after riding all last winter without any issues.

(Jeff Bricker) #7

No resolution from Zwift.

This year I bought a PowerTap G3 wheelset and I’ve been using it outside Zwift (same trainer, same bike, same tire, etc.).  At roughly the same effort level the PowerTap says I’m averaging 250 Watts.

Clearly Zwift was way out of whack, which is unfortunate because otherwise the Zwift environment is engaging.

(Dalibor Skalnik) #8

Having the same issue, I have Elite Rampa freshly calibrated using PowerTap, so my wattage is correct. I am using consistent tire pressure, yet the speeds on Zwift are ridiculously high :frowning: that is a big thumb down for zwift. On zwift I have 36 km/h during an easy ride (outdoors roughly I would have around 30 km/h with this effort, even less). And with a similar effort on VirtualTraining I do around 31 km/h which kind of realistic. As Jeff above points out, zwift environment is engaging, but the speed data put it into the department of arcade games. I guess many people do not mind, but I do.

(Michael Lawrence) #9

Same thing here guys. Mine is basically a carbon copy of Jeff Bricker’s first post. I have about 1,000 miles on my Cyclops Fluid 2 though. In my garage at about 34-45 degrees F. I am using a 700cx23 tire at 100psi, the tension knob is tight until it clicks. All of my personal data is entered correctly. I’m using a Garmin speed sensor on the rear hub, Garmin Cadence sensor, Garmin HR monitor, Garmin ANT+ USB dongle and a 6’ USB extension cable which is run parallel to the bike on the floor and hanging from the outer rear axle. I don’t have a power meter but this I know for sure. I am NOT churning out an average of 269 watts over a 90 minute ride with 2200’ of elevation gain nor am I hitting 600-700+ watts for 10 seconds on Box Hill. Don’t I wish!

I have done all the troubleshooting that I can think of. I’ve reconfigured the information and have paired and re-paired all of the sensors to Zwift multiple times. Trashed the program and re-installed it and used different laptops, and the end result still remains that Zwifts telemetry numbers are embarrassingly high and not consistent. I sure don’t feel good about uploading my rides to Strava with this information. Yea, Strava keeps track of all my data and rides and that isn’t going to change anytime soon.

I even used my Garmin Edge 520 bike computer to see if speed, cadence and HR are the same on the bike v/s Zwift and for the most part they are right on the money. The data sampling rates are different but the information overall is very accurate. That is until you get to about 35mph then the bike computer and Zwift have an issue. Zwift is off by 5-8mph on the high side and sometimes wildly more. It progressively skews the faster the mph. I am typically a 17.5 - 19mph average speed guy but Zwift says typically 22-23mph. Something in Zwift isn’t right.  Luckily I’m on a free trial of Zwift by being a Strava Premium member or I’d be pretty upset. I am very frustrated though now.  I won’t be paying for a subscription until they can get this corrected. 12 days left on my free trial and counting.

It’s too bad that they advertise the Fluid 2 as being one of the supported trainers when clearly it is not at this point. Has anyone tried using a power meter as a baseline then choosing a different trainer model / brand to see if the numbers and power curve are more accurate? Just curious.

Please keep me in the loop on this topic and I’ll do the same.  What a cool program that makes indoor training actually tolerable but until they fix this it’s absolutely useless to me.

(Michael Lawrence) #10

Cross posted more here. Check this out


(James Prosperi SASCC) #11

Michael, yes, see my post in crosslink.

This IS a well know issue. Only way to help is warm up the fluid in the trainer unit. Use a heater, or just spin for 30 minutes before doing serious work.

I have compared to a power meter (Garmin Vectors - which as always consistent and correct for me - tested!) Until it warm up the Fluid 2 will give very high V-Power. After it warms up it is close, within 5% or so I guess, but it will tend to fall the other way slightly i.e. lower a few % after an hour or so. This is from my experience!

So guys can get Massive KOMs etc and win sprints and so on when the F2 is cold, easily. This is the problem with competing on Zwift or comparing figures - it is too easy to cheat. You could even connect a drill motor to your trainer if you wanted… the options for cheating are pretty broad.

If you suspect someone is high, then check their strava results, that will show how consistent they are, compared to the real world.

I really only use Zwift to train in the winter, so I am not interested in competing. Outside is much better!!

It’d be good to see a solution to all this though, make it a level playing field.



(Cory Newton) #12

I’m not on the CycleOps Fluid 2 but a Performance Comp Fluid which is also a “supported” trainer in Zwift. I’m using a Shwalbe booger head tire at 100psi, tightened my adjustment wheel two turns after contact. The standard recommended setting I assume.

My numbers are off the charts!

I’ve done as much as I can to get them back down to reality. I’ve deleted the app (I’m using my iPhone), reinstalled it, unpaired and paired sensors multiple times and even messed with my age and weight numbers to no avail.

I’m guessing I’m about 75 watts too high, but I don’t have a power meter so its hard to tell for sure. I know that a 45 year old man who just started cycling this last March and weighs 235 pounds is not putting out 350 watts for 20 minutes. Not with an average HR of about 135.

However, since I’m not a racer or even competitive (outside of trying to beat my PR’s on Strava segments) I find that whatever the number is will work. I’m looking to improve some over the winter. So if my FTP is 325 in Zwift and I workout enough and it goes up to 350 giving me roughly a 8% increase, then that should translate outside when I’m back on the roads for Spring. Looking at the number now, even a real world 275 watts seems improbable at my age weight and level of fitness. For all I know the numbers are off by a hundred. Yikes.

So the numbers are troubling, but for noobs like me they can be a starting point for improvement.

Hopefully we can get the issue worked out.

Love the program and the iOS app is amazing!



(Mike Mitchell) #13

I have a CycleOps Fluid2 as well, and I recently figured out there is a clutch on the knob… in other words, don’t just twist it two full turns past the touch to the tire. Tighten it until it clicks, and it won’t tighten further. I’ve had extremely consistent power readings since I’ve figured that out. I think temperature still affects the results slightly, but my power numbers seem more realistic now. I just ordered a power meter, but I won’t get it for about 45 days, so it will be a while before I can start comparing power information.

(catherine lyons (c)) #14

hi all, i am having similar which was thrown up by my first race yesterday…and was DQ’d for being over 6wkg for over 5 minutes!  have been doing z2 HR work and all seemed ok but yesterday did the 7 miles race.  speed about 25 mph which i don’t have issue with (on a TT and i can be nippy) but my watts were AVG 283.  which definitley on the high side.  my last bkool ftp was 207.  i did have some internet drops during the race so did work hard to catch back up, and  hit 8.9 wkg.  Just no way!  All weight/height detail ok.  paired via Ant+ - at a bit of a loss.  I also got a QOM and a whole host of PR’s - which is slightly embarrassing if the data is crap :( 

Any ideas?  I have emailed Zwift/Bkool but no responses as yet.