Just finished the ‘build me up’ programme with an FTP of 3.6 W/kg. I fancied trying out a race but, as I’ve never done one before, wanted to break myself in gently. Now, my FTP would suggest cat B but that seems a bit like getting thrown to the lions so would doing the first race as a cat C be cheating?
I think the word you’re looking for is “sandbagging.”
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A legitimate C category rider has an FTP from 2.5 w/kg to 3.2 w/kg.
Yes, I know. But I’ve also never done a race before in my life. That’s why I asked the question
this is an interesting question, and there seems to be a theme developing in the forum for questions along these lines. for the “regular joe” zwifter (which is me), it’s really hard to understand if the numbers you see in zwift are accurate, and all of our experiences are colored by what we see in our own numbers.
here’s what my experience looks like, and why i might question whether your 3.6w/kg FTP is correct. (i’m not saying it’s wrong, just that it raises a question for me)
i’ve been riding zwift for just short of 3 years. i ride more or less 5 nights a week for 1-1.25 hours each session. i push myself pretty hard, and i do C cat races and difficult C and B category group rides, with the occassional D- ride for recovery. i don’t use zwiftpower because i’m not interested in my finish, just the workout i get from the ride, and my own improvement.
i weigh 174lbs (79kg) and my FTP is around 250w right now, making my FTP w/kg about 3.16. when is started, i was 180lbs and FTP was 180w. i’ve been on a kickr snap trainer the entire time, i do regular spin downs (with the correct spindown time in the wahoo app), run tires at 110-120 PSI and have up-to-date firmware. i’m also 38 years old with 2 kids that drain a lot of energy 
i know i can hold 3.75-4 w/kg for about 15 mins tops before my heart rate max is hit. i can sprint pretty hard, and max at 1200w for maybe 10 seconds (decreasing across the 10 seconds).
when i ride a C group ride, i can stay near the front of the ride for the whole ride. based on my w/kg FTP, that makes sense, i’m theoretically borderline B cat. when i ride with a B group ride, i struggle to hang on, but i CAN hang on. again, this makes sense given my w/kg FTP.
if i sprint in a C group ride, i can place top 10 out of 60-80.
if i do a C cat race, i can finish above the 50% mark, and sometimes even above the 25-30% mark, but i have no hope of podium unless i get the right mix of riders. i’ve never tried a B cat race because i feel like C is still correct for me, and i really struggle to hang on to B cat group rides.
i’m slowly improving. my FTP has been inching up slowly from 180 to 250 over 3 years. it’s taken a lot of effort to get to an FTP of 3.16. a lot of that increase has come from pushing myself very hard in races and group rides – not from workouts or solo rides.
so, and i mean this respectfully, because it’s absolutely possible that MY numbers are wrong, when you say that you’ve never raced before but you have an FTP of 3.6w/kg, it seems at odds with my experience. maybe you’re lighter than me, maybe you’re younger, maybe you can ride at a more optimal time of day than me – all of these things could make your numbers correct; but i feel like 3.6w/kg would take a ton of work to achieve, so it makes me wonder.
i hope that helps – if you consistently put out 3.6w/kg FTP and wanted to race B, you’d probably have a great time, and theoretically wouldn’t affect the race. it’s only sandbagging if you’re trying to prove something somewhere else and the number are actually inflated. if you’re consistent, it’s probably fine to race B. if you raced C with that sort of consistent power, though, that’s probably not the right decision – as a C racer that struggles to finish top third (but wonders whether he should be doing B races), i can speak from experience there! 
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I would say register with ZwiftPower and then start with whatever category you want. Zwiftpower will then categorize you based on your race data. If you want to start out in the C’s then go for it as racing on Zwift is a bit different than training and if your power numbers warrant an upgrade you’ll be a B in only a few races.
The legitimate C riders in a C race should not have to compete with A and B class riders, even if the A or B rider just wants an easier ride than they’d get in an A or B race.
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In most races all categories are visible and even though I enter as a B I usually end up racing with a group of Cs. So entering as a B for example is only for results. You can ride with whatever group you can hang with. There are a few races where only your category is shown and this are listed in Zwift power.
Thanks for all your views. Dan, I think you hit the nail on the head - I have no idea how my theoretical training FTP is going to translate into a race situation. Probably best just to try one out and adjust categories after that depending on how I get on. If I wipe the floor with everyone then I’ll move up next time. If I get my backside handed to me on a plate then I’ll move down. Otherwise stick with what is comfortable.
Wish me luck!
You won’t wipe the floor with everyone because there will be other B class riders in the C category races.
And this is 90% of what is wrong with Zwift categories. Someone enters D, doesn’t win despite doing 3.5w/kg because there are a dozen other numpties doing 4+w/kg in a cat that is supposed to have a max of 2.5w/kg. So, thinks they should stay in D cat.
This is what is going to happen if OP enters a C cat race. They will ride at 3.5w/kg because you need to do that to hang onto the lead group in C cat, still won’t win because C cat is filled with people doing 4+w/kg and because OP didn’t win they won’t move up to B where they belong.
Meanwhile, the people who are following the w/kg limits are getting sick and tired of this bull manure.
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It’s worth pointing out that if you’re using or planning to use ZwiftPower’s category system to judge what category you or anyone else ‘should’ be racing in, w/kg isn’t the only metric used. Outright power is also part of the calculation, so looking at w/kg alone (i.e. believing everyone doing more than 3.2w/kg in a C race must be cheating) is flawed. Of course if you disregard ZwiftPower’s system then w/kg is all that matters. Most genuine racers use it.
while you’re accurate and correct, the power limits are so low that only very small people will be using that as their cap rather than w/kg
for the vast majority it’s just w/kg
[slowly raises hand] 
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