Improving 14 watts after a month of solid training would not be impossible especially if you had recently resumed training or had ramped things up a good bit over the month. That said many if not most Kickrs seem to be reading 20 to 30 watts high compared to owners bike mounted power meters so that might explain your not so stellar top speed.

Or you might be as aero as:

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Genetics load the gun, lifestyle pulls the trigger.

Yeah the improvement doesn't just shock me. But at 272 estimated FTP I'm pretty sure I should be well over 23 mph pretty consistently.

Have you tried wearing an aero helmet?

You should be less sure, probably.

There are no certainties in aero.

The kickr may not necessarily be accurate (as in, absolute value) but it's likely consistent. Meaning the magnitude of your gains really is that big. But an 8 minute test? I wouldn't trust and 8 minute test as much as I would a 20 min test. If your FTP is around 3.7 w/kg and not particularly aero, sub 23 mph makes sense. I'm around 3.7 w/kg as well (although proportionally much smaller, possibly less drag) and hold just under 23 mph in an olympic distance bike leg.

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@KellyNCollier

I know now that the estimated FTP from my 8 min test is not indicative of my fitness. Since my 8 min test, which showed that I improved 14 watts, my last 2 workouts I could not make it through. The first one was 3 10 min intervals at 95% FTP. Made it through the first two but couldn't hold the power for the 3rd interval. I chalked it up to the fairly hard 5k I did 12 hrs prior. But today I did a workout with 5 6 min intervals at 105% FTP and think I had fairly fresh legs. Well I made it through first two intervals but the next three I had to take several breaks. Discouraging. I've been following a training plan on trainerroad and this is week 5. What would you do? Should I just keep trucking and see how the next couple of workouts go? Or should I maybe adjust my FTP back down?

My kickr is always in sync with my SRM and Rotor powermeter when warmed up for a couple of minutes.
Sam

Sounds like the 8min results aren't pegging it quite well for you. Since that's the case, you might want to try the 20' (or 2 x 20') tests to get a better grip on the FTP number.

Again, the FTP # is helpful but not a holy grail. If you're not finishing your workouts, you can probably dial it down until retest. Your workout performances also vary depending on run/bike training load - I can do my Sufferfest workouts even at +5% of prescribed intensity if I've taken 1 or 2 days off prior to it, but if I'm in normal daily run/bike training, I can barely survive a one hour at the normal intensity, and if I've just done long rides/runs, I can't even finish them unless I dial it back -5%.

Thank you. I think I will do the 20 min test to get a better idea of where I'm at.

I'd be careful about reading too much into FTP vs avg speed out on the road. There are so many variables outside that can effect speed, not to mention mental and physiological variables with the rider that can effect output while out on the road. Motivation, focus, cooling, the natural movement of the bike underneath you, distractions, etc. can all play in. And of course you have all of the other variables that can directly effect speed like the road surface, hills, turns, traffic, and wind; just to name a few.

Like some others have already said, the important thing is consistency, which you are definitely getting with a Kickr. In regards to your new FTP, I feel like this could be an issue of freshness more than anything, as well as an exceptional performance on the 8 min test. In theory, FTP is the power you can hold for an hour. With these 3x10 intervals at 95% of your new FTP, they are almost the same as doing 3x10 intervals at 100% of your previous FTP. In theory, this should hurt really bad but definitely be possible. With that in mind, I'd recommend taking a thorough self-assessment to see if you may have some lingering fatigue from your last block of training. Perhaps a rest week is all you need and you'll be good to go. If not, I'd recommend giving that 20 min test a try before jumping into your next block. Completing workouts is the first priority and just guessing what your FTP is and beating yourself up each time you're on the trainer is definitely not conducive to building fitness (or happiness for that matter). Hope this helps and feel free to reach out to me directly if you need some further assistance with this.

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Professional Mountain Biker and Community Manager at TrainerRoad - Cycling's Most Effective Training Tool