Converting FTP to a 40k TT power target

Are there any calculators, or even just a rules of thumb, out there for estimating a 40k TT power target based on your FTP?

Or to put another way, a question for all TTers, esp triathletes: what’s your FTP and what power do you aim for or hit over 40k?

Thanks in advance!

I look to be around my FTP for what is for me about a 65 minute ride.
I don’t look at the power as I just push as hard as I can and it ends up close to FTP. The main thing is to keep pushing on the pedals. If you ease off even just for a few yards when you let yourself coast, and it is quite a temptation to do just that, then the power does drop off.

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The most important thing to know is how long you can actually hold your ‘FTP’ for and adjust your percentage to get you through the whole effort.

The reason I say that is that, depending on the method of testing FTP, your time to exhaustion at your tested FTP can vary wildly, sometimes to the extent that there is no way you could reasonably describe your test result as FTP. Typically time to exhaustion for a steady effort at FTP is anywhere between 30 and 70 minutes, depending on how well trained you are.



Take a look at Best Bike Split…


This. Although I do have a lap power field on my head unit (set to 1k intervals for 10’s and 25’s and 5k for 50’s and longer) I don’t really race to power.

I use WKO4 to calculate my time to exhaustion which is their metric for how long you can hold FTP. For me it’s around 55’ which is, depending on the course, around 40k.
For triathlon, I use 90-95% of my FTP for an Olympic distance race


Just reading into the question a bit more you ask the question to tters and triathletes -
To answer your question first i’ll back track a bit - i find i have different figures for a indoor vs outdoor ftp test - in the summer i do local club 10mile time trials i use these as a guage of my 20min power (im usually around the 21/22 min mark) - from these numbers if im riding a 25mile tt (40k tt) im either aiming for a hour or under depending on the course i can ride at my outdoor configured ftp if i were new to it id aim for around 95% for the first half of the race and then recess for the second half if i want more or less power, theres a learning curve to pacing and time will ulimately help you in your quest for that perfectly paced tt - now onto the triathlete part , as part of a triathlon leg a rule of thumb is between 80 and 90% i normally end up at around 85% and a little more for a flat course , hope this helps …oh and a 2x20 at ftp is a good guage on the turbo if the numbers are sustainable for a 40k in my experiance

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For what it’s worth, I held 300w to do flat 40k in 1:02 on an aero but not a TT bike. But there are just too many variables I guess

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It depends. My FTP on the trainer is a bit different to what I can do in my aggressive position outdoor. To give you some idea for me I managed to sneak under 50 minutes for 25 miles at 0.95IF but also did 54 minute rides at 0.97IF too last season

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Just adding that you may want to test your FTP with the 20 minute test, rather than the ramp test, as it is a better representation of the energy systems used for a 40km TT effort.

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That’s freaking killer!

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Oh that’s interesting, I didn’t realise it mattered. I joined TR just as the ramp test was released, so haven’t had the need to do a 20min test. Might swap out a training day in next few weeks to test it.

Do you have a 40k TT race in your schedule this season? I only ask as pacing a 40k TT is very different then using a power target. Different course conditions, wind/weather conditions will dictate how you meter out your effort for the best results. For example 2 races from last season 40k 52:06 263AP/264NP and 40k 53:22 277AP/280NP based on 281w FTP.

At the upper levels of the ramp test, you are bringing in the anaerobic energy systems, while the 20 minute test is more aerobic in nature (as is a 40km TT). They normally produce pretty similar results, but if you have an anaerobic strength or weakness (as compared with the average), it could be a handful watts different. If you are asking about percentages of FTP for a 40 km TT effort, I assume you are trying to dial things to within a few watts, so in this context, it might matter.

And a 20 min test is probably good mental preparation for a 40km TT. :sweat::slightly_smiling_face:


The short answer to your question is that your FTP alone will not provide you with any insight as it is a single data point.

If you have a lot of all-out efforts in the 20-90 minute range, you can estimate your 60min from your Power Duration Curve. If not, you could swag it in the following manner:

a. If your FTP is recent and if you have had a steep ramp to it, your TTE (see below) is probably in the 30-45min range and thus likely that your hour power is 80-90% of your FTP.

b. Conversely, if you FTP has been steady and you have been doing a lot of progressive intervals in each of the training zones (SS, Threshold, O/Us), you’re probably in the 90-105% range for the 40k TT.

There are also a couple of great suggestions in the posts above that I’d like ti highlight:

  1. Execute Dr. Andrew Coggan’s 20min FTP test as defined in “Training and Racing with a Power Meter”. Key elements include the early ramp to sustained power and the ramp during the last few minutes. It is how world class TTers execute a TT and Andy’s FTP test is great practice for the rest of us.

  2. Use WK04 to measure and monitor your Time to Exhaustion (TTE). TTE is a great measure of how long you can sustain your FTP. If you do progressive intervals mentioned above, you will see how you can drive your TTE up.
    FWIW: When I started SSB MVI my TTE was in the 30+min range; by the end I was 1h 03mins. After doing Andy’s 20min test that led me to raise my FTP, I’m back in the high 30s (the reward for hard work :slight_smile: ).


This is a good question. I’m following the 40 K TT Plan to improve my bike portion of sprint and olympic distance triathlons. So far, I’ve found I can’t make it through the sessions like Dunderberg-1 or Dardanelles-1 (they’re 4 long blocks with short breaks close to 55 min. long) even though I can complete the other sessions in the plan.

I’d agree that my current actual capacity to hold pace for an hour would more likely be in the 80-90% range of my FTP.

If you’re following this plan, there is a 20 min FTP test scheduled as one of the sessions, so I imagine this should give me a better idea of my actual sustainable output as opposed to FTP/potential output. It does make me wonder if the ramp test is really one-hour power or more of a fitness assessment value. It seems to be a good number for anything other than sustained power.

Do Farquhar in the body position you expect to use to get used to what the effort feels like.

Then, you can go to best bike split or to get a rough estimate of what your watts will need to be to hold 24.85mph if you want to do a one hour TT (it’ll likely be somewhere between 275 & 340 depending on your body position and equipment).


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