Power required for a 40kph TT

I’m curious about power required to average 40kph or more on a flat TT course that’s not too technical, i.e. no roundabouts or other obstacles you need to slow for.

If you can share your

  • Average speed
  • Distance
  • Your height
  • Your weight
  • Power measurement device
  • If it’s outside or on zwift for example

Also keen to hear if disk wheels make any difference.

I’ve done my own measuring for me but keen to see what faster riders do so I know what sort of power is required.

Thanks in advance :slight_smile:


Average power: 234 W

42.4 km/h
90.38 km
170 lbs
Powertap hub
Felt IA Triathlon bike, Hed jet disc rear, Hed Jet 9 front, skinsuit, Giro Aerohead, Giro Empire shoes, defeet evo disruptor socks, wax based drivetrain, 23 mm GP 5000 w/ latex tubes, 90 psi front, 95 rear



Different helmet and shoes, and no socks here ( older pic from a triathlon ) but gives you an idea of position. Also my sleeved tri suit instead of my cycling specific skinsuit.



My PB this year was not my best power but it was a nice day with not much wind -
25miles (I live in the UK - 40.225km)
61kg/135 lbs.
Was a 2 lap course with roundabouts at each end so 4 of them.
Favero Assioma power pedals
I did manage 251W for a 25m TT earlier in the year but that was a tough sporting course

As an aside as mentioned above I managed 1:51:37 for 50miles off 233W on 4 laps of the same course (the F2/25 and F2/50) in Cambridgeshire if you live in the UK - which is 26.9mph. Plus 20:32 for 10 miles which is 29.22 mph off 264W - so the answer is less power than you think if you are not big and get aero. Plus I had an aero bike fit yesterday so I’m aiming for a 30mph 10 next year off the same power… :pray:


Is that a Exocet.?

Yep - it’s the Exocet 3 from Planet X - it doesn’t seem to be sold anymore and is a lot less common than the 2 which was around for years - does the job and didn’t require a second mortgage! :grin:


Every course I have been on I think is technical by the OPs description (lots of roundabouts). I don’t think I trust my power meter for my PB though, 56.59 on the F2A/25 it says 296w in the wet. However, all my other TTs in the dry have been fairly consistent.
My best dry 25miles (40.2km) was on the B25/8. It has a short country road loop to start, goes through 4 roundabouts and over couple of miles of patched concrete road. So I reckon you could get away with less power for the sane speed on another road. Anyway for:
25 miles (40.2km), I averaged 26.1mph (42kph) for 224w NP (57:31).
I typically weigh around 59kg
I’m 5ft 9 tall (175cm I think)
I record on a Favero Be Pro S
I use a disk and it seems to have made a big difference but the biggest improvement for me has come with finding a comfortable position I can hold.

Not 100% comparable (if at all :roll_eyes:) in 2019 on the course with the same wheels but a position I couldn’t hold (especially over the broken road) due to damaged wrist; I averaged 24.2mph (38,9kph) for 251w (for 1:02:12). I have not done the B25/8 without a disc but looking at our club sporting (quite technical) 10 (16km) a disc saved me circa 35s.


the last time I did a 40k was in 2010 on my regular road bike with my Mavic Open Pro+Powertap training set.

six one, 165lbs, and it took a little over 320w to crack an hour on a gently rolling course with two turnarounds and straight roads.


That is awesome speed! Kudos! What tyres are you using and do you recommend those over socks?

Thanks - I use Conti GP5000 25c with latex tubes - I did use Corsa speeds tubeless for a few races last year but I got a sealant leak in the carpark before a hot TT last year and don’t trust them - according to the Bicycle rolling resistance website if you use latex tubes the GP5000 are only about 1.5W slow than the Corsa speeds and they are much more robust. I wear a Nopinz flow suit which is a seriously quick bit of clothing along with Castelli fast feet overshoes which as you can see double as aero socks! :grin:

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Great info. thanks! I have GP5000 25c front and rear on my road bike, 23c/25c front/rear on my TT. I’ll look to get a set of those overshoes. I guess I should look into a skinsuit. At the moment I either just wear the Castelli Aero jersey or my tri suit. I want to go 25c front and back on the TT too, but am too tight to swap at the moment because there’s so much wear left on the 23c. lol.

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AP222W NP241W
Avg moving speed 39.6kph
40km 1h02m
Powertap P1S
London Triathlon

AP264 NP267
40km 1h01m
Powertap P1S
Zwift Tri Academy 40TT Race

the B25/8 is quick though …if rather uncomfortable :grimacing: My 54:20 this year in the ECCA event came off only 237W - typical early morning Sunday snooze power! It may do your body no favours but when the resurfacing is finished which they were supposed to start the day after the race there won’t be many quicker courses! :laughing:

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Lol, Unless you are as daft as me :joy:

I did it once, where I headed up the slip road after the bridge at the start and thought “this is taking me to nowhere”, doubled back and turned left, then decided I was right in the first place and double backed again. Went to turn right and had to give way to a couple of cars. It at least got the HR up though (according to intervals it was my max LTHR, 92% for an 1h1min28s and a similar NP 222w; coincidentally 40kph).

I knew then though I’d comfortably break my target of an hour for a 25, which I did 8months later on the F2A/25 (on a float day). The B25/8 4 months was only 32s slower on a windy day so Im sure you are right once they resurface it, on a good day, it’ll be the fastest in the area :+1:

The E2 claims to be but I’ve only done a 10 on it and going by my limited experience, its 40s slower than the F2A/10 (although not comparable conditions).

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The problem with the E2/10 or E2/25 is they are not consistent. The F2A/25 or 10 will be quick …ish in anything bar a gale. Same for the B25/8. The E2/10 (and the same for the 25 when the road works are done) can be lightening fast (I did a 20 on there this year) but on what looks (until you get out there :grimacing:) a similar day it can be a minute or more slower. In addition the E2 is quick with an E/N/NE wind but slow with a SW…guess which is the UK prevailing wind direction :roll_eyes:

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  • 24.8mph (bang on 1 hour)
  • 24.8 miles / 40K
  • 204w AP / 209w NP (1.02 VI); .78 IF
  • 5’9" / 175cm
  • 150 lbs / 68kg
  • PowerTap hub

It has been quite awhile since I have done a pure 40K TT…the above is basically the first hour of IM Muncie 70.3. Course is about as flat as they come…only had 300 ft of elevation in the split above. pavement was butter smooth and FAST.

Castelli Speedsuit, Giro Aerohead, Shiv TT (w/ nosecone), 808 FC Frt / Zipp Disc rear (tubular).

Obviously this was not an all-out TT effort since it was the beginning of an IM 70.3 and I still had 50K left to ride…would have loved to have given it everything on that course to see what I could have done at full speed.

(Final split was 2:19, 24.1mph, 192w AP / 198w NP)


First time going under the hour earlier this year.

Giant trinity
60mm front
80mm rear
4iiii left crank power meter
Course wasn’t flat but certainly not hilly, 3 RAB’s 90 degree/180 degree/270 degree turns.
Was a wet day and spent the first 10k with a steamed up visor and the other 30k with the visor upturned.
Went faster later but this is the closest to the question

  • 25.5mph
  • 100 miles
  • 5’8”
  • 150
  • Favero Duo Pedals - 228w Avg
  • Outdoors on a 50 mile out and back country road route.

This was on my Speed Concept TT bike. Disc wheel in the back and 50mm wheel up front.

Give me a follow on strava :+1:


You’ll need about 1000 watts/CdA.


Hi Robert…can you expand on that a bit? If I am understanding you correctly, if cda = 1.0, then you would need ~1000w to go 1 hour?

So in my case above, with a 204 AW for spot-on one hour, my cda would have been ~.204 (which would align well with my ERO testing)?