After a bit of advice
 

If your FTP is continuing to increase, I'd keep doing that until it doesn't.

Since you have a coach, I'd utilize that person as much as possible.

Other than that, continually refining position and studying up on appropriate equipment choices (including what you'll wear) could provide a good bit of extra free speed.

Know what you are training for. A short quick sprint or a long ride with lots of hills. Even for a TT bike level and all out will be different than hills and all out.

But as long as your numbers are getting better and you like the way you are doing what you are doing. Then keep on. When the numbers plateau, you might need to change something. Sometimes it's just a temporary change.

And if you use a coach, are they just for one thing? Or are they looking at all you do toward what ever your goal is. If they are looking at the bigger picture, then trust them before us.

You're going to need to increase your power. A lot. You'll need to be able to sustain 220–240 W for the duration. Check out this calculator. Your weight won't make a big difference in the final result.

I think the typical recommendation would be to ride long intervals (8–20 minutes) around your threshold (90–105% FTP) with 3–4 minutes recovery between intervals. One of my typical workouts is 4 × 10 min @ 105% and it's really tough. For me, at least.

This is a very eye-opening thread in regards to the power necessary to obtain specific speeds.

It gives a good indication of what may be possible when your bike and position are optimized.

https://forum.slowtwitch.com/forum/S...race_P3499977/

A five hour time trial position has to have comfort as the centerpiece, though.

What was your average speed for the 8.3 mile TT?

21.5mph on a lumpy, exposed course.
My fastest 10 has been just over the 23mph mark.

Speed is the only thing that matters in time trial. Notwithstanding that, power is your currency to buy speed hence the more power you have the more speed you can buy for your cost curve. And you can improve your cost curve such that speed is cheaper to buy - less body weight, more aero equipment, better position, faster tires, less difficult terrain and wind conditions and lower air density.

We have a local time trial corse and typical speeds on a flat 20k course, low wind and smooth pavement for women are 24 -27 mph and men 24 to 30. And the racers are pretty optimized for time trials. Of course, the speed may be slower.

If your are getting 23 mph on a flat course with 180 watts, you are doing good. There is no way I can generate that speed for that power. 180 watts generates about 20 mph with everything optimized and in my fastest tested aero position and creeps up to more like 195 - 200 watts with a training versus race setup. At the indoor velodrome 20 mph is more like 170 watts depending.

My purpose for the discussion is can you believe the metrics that you are getting?

Your power looks low for the speed but depending on gender / stature, may be okay.

For training, follow coaches advice and ride a lot on your TT bike. I like to do most of my hard interval workouts on the TT bike and save endurance riding for my road bike. If you want to ride 100 miles on a TT bike, you will need a lot of saddle time in the TT position.

I'm a 5'2" female weighing about 60kgs if that helps? It is possible my FTP has gone up. I haven't tested it since late June/early July (can't remember if it was before or after my holiday), and then TTs were allowed to start, plus I continued with my twice weekly turbo sessions. Both TT PBs were the end of last month, after my bike fit as well. I have an FTP test booked in with my coach next week, and then we'll begin to formulate a plan for next year.

I danced around the question of male / female but thought you were probably female by the speed / power. My wife is a gonzo time trialist / pursuitist at 5’4” 48 kilos. She can generate 25 mph out of
~185 watts flattish road conditions and definitely at the indoor track with a double disk set up. You are in the hunt but may need some work on your set up / equipment to get more speed per watt.

My wife and I have been racing consistently for the last 12 years time trials and track pursuit. Lately, we have been doing a lot of team time trial 20k/40k efforts hour of power style workouts. They are a lot of fun and IMO, build a great aerobic engine. You go fast and put in slugs of power such that the normalized power for the hour is around SST and the exchanges require anaerobic pops to get on the other persons wheel. And you do not have to run the engine too hot. The main point is constant effort for 40K.

Holland? Go to M5 in Middelburg and buy/rent an M5 High Racer. Waaaaay more comfortable than even the least aggressive TT position.
M5 Recumbents » Models » Carbon High Racer

While that link claims 48.3km/h @ 250W (on the track), I can at least confirm 22.5mph at 200W for a 85kg rider on a Hollish-like flat road course, and sub-5hr centuries are achievable by a duffer.