Estimating Target Power for TT

Has anyone got method/science to approximating a target avg power for a 25km TT? I’ve been doing nothing but TR workouts and road races for a while and this has come up. I was thinking of having a go on a road bike in our local club TT (having just had a win in the road race in the series). The course is undulating but no real ‘climbs’. Just a few pinches maxing 4-5%. I am thinking the achievable number is probably around or just above threshold? That should be about 45-55 mins I’m guessing (or hoping). Any help would be much appreciated.


I’m certainly not the best TT’er but I aim to break a sub hour TT in to 1/4s and go out in the first 1/4 at FTP and build on it if I’m feeling it.

Depending on how you determined your FTP, the target around threshold makes sense in general.
If you did a 20 minute test, you might find out that you will not be able to hold your FTP20 (.95 of 20‘ average) for a full hour. At least for me, the gap is bigger than 5%.
Also, when doing a 20 minute test or ramp test, you will likely focus on power over everything. I tend to get out of the saddle a good five thousand times during a 20 minute test. That of course doesn’t make sense during an effort were you want to be fast over everything.

My advice:

  • it is likely you will not be able to push an average power over your FTP for 45+ minutes.
  • focus on speed over power. Power is a great support for pacing your effort, but especially average power can be deceptive. Especially on an undulating, windy or technical course, variability can make you faster than a perfectly even effort. Adding the data field NP might be helpful. If that’s close to your target power, you did well! Push over target power on the ascents, below target power on descents (that’s not all out on the ascents, soft pedaling on the descents -mildly go over and under target power. Maybe 10 to 15% over on the ascents and 10 to 15% below target on the descents // push over the crest of a climb to gain speed again, don‘t stop pedaling right at the top) - take as much speed as possible into corners (don‘t push hard into a corner, brake hard, and have to accelerate hard again - these small breaks can do wonders)
  • focus on position over power! The most aerodynamic position will likely not be the position where you can push the most watts (likely below your FTP result). Nevertheless, a lower position will be faster than pushing more watts in an upright position. If you struggle to hold a super low position (bend arms hoods) position for most of the race, alter the position according to the course. Position matters most, when aero matters most (head wind sections, descents, other high speed sections). If you need relieve (ie get out of the low position), do that on the climbs or tailwind sections.
  • target power: slightly below FTP (even better, do a hard effort in position before the race, I usually do long Strava segments as fast as I can, so I know which power in a fast position works for me). Don’t start out too hard. If the course starts fast (downhill, flat with tail wind), you are lucky, start below your target power and you won‘t lose much time!

So that’s all the time for me :joy:


@Aeroiseverything made a lot of great points. A recent 33km TT I did 315AP/338NP and my FTP is 330.

Edit: post the Strava segment/course profile and we can give you advice about roughly when to put down power, ease off, etc

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Nice TT, pretty demanding course!

→ also, best bike split can help you with pacing. Factors in climbing and wind.

It’s a wonderfully brutal course. 5 minutes @ 115% FTP halfway through a 55 minute effort feels so weird haha

Agree re: BBS :+1:

Learn what threshold feels like. Breathing heavily elevated but not ragged.

Get an idea of what it feels like to hold that effort for a long time and what happens when you run out of juice.

Get a ballpark wattage number that matches up with your threshold feeling.

First third ride to the number. Middle third ride to being on the edge of being out of threshold based on your breath. Last third go as hard as you think you can manage given the state of your legs.

The power meter is there to give you an objective measure until your subjective perceptions can catch up.


Thank you everyone, this was very helpful. (though due to illness i missed that TT). I’ll pocket this excellent info for the next one!