Newbie question on numbers in Zwift on different bikes

(Cardoon) #1

Hello all!

I am new to Zwift and the forum, as well as to bike training. I am not new to biking, but the numbers game is totally unknown to me. So I do not really know how to ‘read’ the numbers. Maybe more experienced Zwifters can help me out?

A little over a month ago I got a smart trainer (kickr snap) loaded my XC mtb on it -only bike I had- and got onto Zwift. Loved it, so got a subscription and a cadence meter and heart meter.
My first few rides and an FTP test were fine for as far as I know. FTP was about 142 if I remember correctly. I am nearly 49 so do not know what to expect, what a good ftp is for someone my age who never took interest in training before. But I had a few one hour+ rides where my average watts were around 140-150 watts.

Then, when spring got really underway, I got a fifth-hand Trek Lexa roadbike so I could go outside on my own mtb. The Lexa is now my “slave” bike that is in the trainer permanently.

But my average watts and FTP dropped dramatically. I had a headcold at that time, nothing serious, just a blocked nose and forehead so I would expect some loss of power, but I am not sure if it should be this much? Before the change, I did the mountain climb in Watopia in 38 minutes. Now, I cant get it any faster then 41 minutes.

I did a new FTP test and got it on 134, nd my average watts consistently stay around 125 over the whole ride.

My question is: Is this normal? Or am I doing something wrong? If so, what?

Is it the change of bike on the trainer that gives such different output/readings?
Is it the headcold? Can that make such a big difference? (And shouldn’t it have cleared by now, two and a half weeks on?)
Did I maybe put the bike too loose or too tight in the trainer? (Rear wheel does not slip though…)
Does tire pressure count for so much? (pumped it up hard just to be sure. No dice. Still much lower output then what I saw before)
Or is such a drop normal and should I just get on that trainer more?
A combination of some or all of the above?


(Gerrie Delport TeamZF) #2

It can be so many things so I will start with the obvious ones.

Did you calibrate your trainer after you swapped bikes.
Different bikes could have different gearing so you may be not selecting or not have the same preferred gear as before.

How old is the “new” bike, it may need a service dry bearings and chain can cause significant losses.

Did you use clip less pedals with the MB and not with the “new” bike?

1 Like
(Cardoon) #3

Hi Gerrie, thanks for your input. If calibrating the trainer means doing a spin till 37 kms and then letting it fizz out, I have done that twice. I noticed it was a lot easier on the mtb to have zwift think i did 37 kms already. Is there a different way of calibrating the trainer?

But a mtb has indeed very different gearing from a roadbike, so that might be a thing.

I have clipless on both bikes. The lexa needs a tune up for sure. Maybe i’d better plan that a little earlier then i originally envisioned.

(Cardoon) #4

Maybe I am simply unacustomed to numbers and maybe I am underestimating the amount of power that a headcold can take away from me, but after a few rides this week where I consistently had my FTP upgraded by the app after the ride (in three steps up to 151 now) and feeling quite well, I am starting to think it was not just the bike.

Dang headcolds!

1 Like
(Gerrie Delport TeamZF) #5

Good news that the power is going up up up.

(Aaron Zwanzig [DIRT]) #6

I have a couple thoughts about the difference in wattage between the bikes. The 5th-hand road bike might have points of excessive friction in the drive-train causing a loss of power. Your planned tune-up might address that. Also, the road bike likely has smoother tires than the mtb, leading to more slippage on the trainer roller. You might try using a trainer-specific tire. Good luck!