Help Needed to Understand my Metrics


I’m relatively new to Zwift, and am riding a Schwinn IC8 indoor bike (same as the IC4 sold in the States). I have entered three races now and am trying to make sense of the data that Zwift presents me.

I did the 3R Figure 8 Hilly Race Cat B - 1 lap (29.2 km) race this morning at 0810 UK time). My FPT was 282W, updated by Zwift following my previous race – at 82kg that gave me a w/kg figure of 3.4.

I finished 16/20, and my race results data were:

HR : 137 AVG, 162 MAX
TIME : 44.52
POWER : 335W
W/KG : 4.09

Cadence : 74 AVG, 121 MAX

As I understand it, the IC8 provides a power reading to Zwift, but Zwift cannot control the resistance level of the bike. For this race I left the level at 38 (the IC8 range is 0 – 100). I notice that when going up a hill, Zwift slows my speed down, whereas on the bikes own display it is unchanged. As I am not changing the level myself, I maintain the same Cadence. One final point, I get the little lightening symbol next to my W/KG on the Zwift board, so its not using zPower (?).

What I don’t understand is that on the Race Results sheet, my displayed power of 335W and my 4.09 W/KG seems quite high. The guy who finished 1 second ahead of me had an average power of 218W and a W/KG of 3.69.

I’m not expecting to be anywhere near the top, and was quite happy with my position, and certainly felt like I’d had a good workout. But can anyone throw any light on these figures? Is Zwift compensating/correcting the IC8’s power output? And how do I improve? Do I increase my average Cadence? Do I play with the bike’s resistance levels during a race?

One final thing, at the end of the race, Zwift announced that my FPT had increased to 338W which gives me a W/KG of 4.1! And a pass into Cat A races (at 58, is it too late to chase an Olympic dream? :smile: :grin: More seriously, a W/KG figure of 4.1 is too high for me, but if I now attempt to enter a lower category race, I might get accused of wrongly entering races below my Zwift category and get disqualified.

First issue is dont race with this bike, it is very well documented to be miscalibrated, search the forum for the relevant thread on this topic. It is extremely likely that your power is grossly overestimated.

Second, read this thread about how speed is determined, it should answer your questions about why you were going slower uphill.


This means that he/she was better at conserving energy and sitting in the draft. They outplayed you with race tactics.


If you race on that trainer then use cat A.



It’s been a few months, but maybe others will benefit from this comment. The IC4 / IC8 bike needs to be recalibrated from the factory. There is a process for this in the manual. You only get 3 calibrations on the monitor, so don’t do what I did and start that process without a firm understanding about the reset. The process is simple, but the recalibration of the top end resistance is where all the inaccuracy exists. The 0 end is easy as no resistance is well 0. The top end require you to increase the resistance to the end of the mechanical range. Unfortunately, this will put the functional range of resistance down to the bottom 1-30 on the 0-100 scale. When I set the 100 resistance, I got on the bike and attempted to pull down on the pedal. I’m a pretty strong guy. I weight 220 and I can deadlift around 400, so I think I should be able to “move” the pedal near the 100 level. Here in lies the major flaw with this set up, it is all on feel. Unless you install power meter pedals, you will never be sure you are dialed in. I was putting out 400 FTP rides prior to the recalibration, now I’m at 212. While neither are accurate, I’m probably much closer to the current setting. To ask someone to never race is not really fair. You are paying for the app, so enjoy all the features. Racing is a great push and motivates the training, so…

Best of luck and sorry this was such a long post. It’s an odd problem that doesn’t’ appear to be well discussed.

Hi Mike, I installed some Assiomo Uno’s just this weekend saw a drop of about 100W - i need to redo an FPT test. I have not recalibrated my bike, mainly because of the 3 limit, but also I could not be sure if it was going to make a difference. Anyway, with power meter pedals fitted that issue has gone away. Now I can concentrate on my training and race times!