I’m trying to get a better understanding of w/kg as it relates to ftp, gearing, and going up hills. To spare you the details, let me cut to the heart of my question: is it possible for a 200 pound rider with an FTP of 175 riding a bike with a 53/39 group set, typical cassette, to go up a 5% hill and find a gearing combination allowing the rider to maintain the same FTP/w/kg as if he were riding on a completely flat surface.
w/kg does not directly relate to FTP
As far as I understand it, you could achieve the same watts, and therefore w/kg, regardless of gear ratio (well mostly any typical ratio) for the same weight+incline, but the cadence and type of muscle recruitment will vary significantly (as you change gear ratios). Depending on your training you will find you only are only able to pedal smoothly up to a certain cadence, this will be more of a limiting factor to the gear ratios you can use to achieve a particular power output (watts) than anything other than strength.
w/kg is literally your power output (watts) divided by your weight (in kilograms). Since w/kg is used to calculate speed in game we can see that it is a useful tool for tracking how likely you are going to catch up to, get dropped by, or keep up with, another rider as incline changes, regardless of rider weight differences. That is, if you focus on matching your w/kg (not your watts itself) to another rider you should be able to keep up with them without having to think about how fast either of you might be going.
FTP is an estimation of what power output (in watts) you would likely be able to maintain (assuming you are using the ideal cadence) for an hour. FTP is not affected by weight but if you know your weight you can calculate an estimate of the maximum distance you could travel for a given incline/resistance in one hour. Because the type of muscle tissue used at different cadences for the same power output varies somewhat, the amount of time you will be able to sustain that power will likely also vary. You may also notice, depending on your training, that different muscle groups will vary a bit at different cadences (I am still a novice so I’m not sure if there are ideal muscle recruitment groups depending on the type of riding you do, or if you should always be mainly using one group. I think sprinting tends to use a lot more of the quads and enduro make more use of the glutes? maybe?).
Zwift uses your power output and the weight you enter to calculate w/kg and subsequently speed for a given incline in game. Depending on the type of trainer you are using you may find yourself using vastly different gear ratios for a given speed+incline+w/kg in game to real life, but you should in most cases still be able to use the same cadence+watts in game as you would in real life, which is all that matters for a workout anyway.
In short gear ratios don’t matter that much other than to get the right cadence for a particular power output. You should have no trouble maintaining a power output you are comfortable with, for most inclines, most rider weights, and most typical group-sets.
Yes. You can adjust the trainer difficulty setting within Zwift so that the effect of gradients on the resistance can be reduced (or increased) to none. You can ride up mountains with the same effort as on the flats or descents, if you wish, but your speed will still be influenced by the gradient even if you cannot feel it.