Power required for a 40kph TT

I could be talking garbage but I have seen some amazing myWindsock CdA’s on DCs which aren’t possible. I suspect that the power needed when you are dragged along by traffic is a wee bit lower again messing up the CdA calculation.

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Oh, absolutely…I especially noticed that effect when we used to do Spring Break in Sanibel, FL. I would do endless laps of the island and the impact of traffic on my power was very noticeable.

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Maybe but the stop signs and wind equal things out :joy:

Not on Sanibel Island!!..basically non-stop from one end of Sanibel-Captiva Road to the other…(~10 miles)

True… the main drag (Periwinkle) only has one stop sign from west of the causeway to the almost tip of Captiva.

Let me know next time your in town and want to smash out some miles!



Will do!! Been a few years since we have gone down for Spring Break, but want to go back.

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If I’ve learned anything from this threat it’s that I’m basically a human parachute, haha. The speed to power ratios are mind-blowing to me!

265W average (269 normalized) as read by a Powertap P1 pedal got me a pedestrian 1:05 at my last oly tri on a rolling course. On an older felt B12 with shallow rims, round bottle on the down tube, non-aero socks/shoes, hairy legs, butyl tubes, to be fair. BUT: skin suit, aero helmet, clean and waxed chain, which I figured were the big ones. 5’11” & 175 lbs. I know I have low-hanging fruit, but 5+ min worth? :thinking:


1:05 is nothing to be sniffed at. I reckon it was the waxed chain, not the hours and hours of training that got you there :wink::wink:


Thanks I am not familiar with this so will read up :slight_smile:

I’m with you on that, my power isn’t as good as yours, I can only sustain around 240W but that only gives me a 35kph speed average. I’m a bit taller than most of the riders here at 188cm (6’2) and 81kg but I wouldn’t think that would make such a difference. Maybe my ‘aero’ position isn’t that aero so will check that out, but like you said I’ve done all the other things to maximise speed. The only other post here that seemed to match what power I will need is RobertK’s but if I need that much I have a lot of work to do


Wow, that power is so much higher than others here! From what I’ve seen with power calculators that’s around what I’ll need too as I can only manage 35kph@240W. I’m 6’2 and 81kg so maybe the extra height is creating more drag and maybe my aero postion really sucks

To be clear, you’re in the aero bars on a TT bike?

I just looked at bikecalculator.com, and got just under 40kph at 240 watts and your weight in aerobars, and just over 35kph in the drops.

All of that is incredibly variable, but assuming you’re on a TT bike, you likely have some low hanging aero fruit.

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  • An outside ride of 40km in length @ 35km/h, at a cost of 253W avg, measured by Favero Assioma Duo.
  • I’m 183cm, 71kg
  • Canyon Endurace AL7.0 with tri bars. So the bike is super-non aero, but my position is at least lower.
  • Standard cycling bibshort + jersey, standard helmet, non-shaven legs.

Reading dfquigley, I’m starting to believe that higher speeds are possible for me too. Apparently I’m super non-aero.

Swiss Side implies it costs 180W for 35kph and 350W for 45kph, so your 42kph at 234W looks highly optimized.

that was in the drops on a regular road bike, with 32h box rims. I also wide shoulders so I’m not very aero, even with narrow bars.

the same power on a TT bike with aero wheels was over 5 minutes faster on the same course.

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Average speed and distance from GPS data. Outdoor 40km course, out and back with one intersection turn.
25.2 MPH / 40.55 KPH
24.41 Miles / 39.28 Kilometers

Rough measurements of me
6’2" / 188cm
176lbs. / 80kg.

Power from Quarq d-zero generation
321 AP / 322 NP

Stock road bike with 60mm deep wheels


Fair point - probably a more accurate metric for me is the 56:48 I managed up at Bungay on the B25/50 early Sunday morning October 3rd this year in the NABC25 - my last TT of the year. The course is pan flat but is single carriageway and there is very little traffic early Sunday. There are 3 180 degree roundabout turns and a roundabout you have to go straight across 4 times on the 2 lap course (slows you a bit) but it’s reasonably brisk for a single carriageway course. Was pretty breezy - 9.4mph SW wind but not ruinous - that time was 26.4mph and needed 247W :grinning:…it was also my best 25 of the year on Spindata…which you but probably nobody else on here will have a clue what I’m talking about :laughing:

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Nice one :muscle:
I’ve only done the Bungay 10 myself. Lol I was down for the 25 last year but after a night of torrential rain and gales I decided that a trip from Peterborough to Bungay, only to find out it was cancelled, wouldn’t be a good idea. My main reason to do it was to beat the hour and with the winds I wouldn’t have anyway. I think it did actually go ahead though.

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Course and conditions make a huge difference. Quite a few of the posts in here are from UK TTers who are doing courses which are ideal for high speeds. I.e. dual carriageways where you have a steady stream of traffic passing you and giving a draft benefit, very flat, smooth road surfaces, nothing technical other than maybe a roundabout at the halfway point. A course like that could easily be 5kph faster than something with a few rollers, sharp turns, sections of crappy road surface, etc.

True - courses can be quick as you say - but UK TT has caught on to the CdA obsession - I had an aerofit on Monday to overhaul my position and it’s been completely changed. Wind tunnel testing, skinsuit tech from Nopinz etc and a lot of coaching, physiology discussion on our TT forum…most of which I don’t understand and I teach science! All of that has made a massive difference - and we don’t need to be UCI legal for CTT events. Finally at the pointy end some of the guys have world tour level power (if not the recovery abilities and road racing credentials) so it isn’t just the courses - the sport has very few racers who are not training really hard and using top of the range kit.


There is definitely an element of that, which I hope I have inferred above, but on a lumpy, poorly surfaced and technical sporting course with no traffic to drag me along, I am slower but only by 3.7kph. @jdman also gives a good example of a flat and non-technical course (the B25/43 at Bungay) which for him is only 2.6kph slower than his DC time. So it’s not all about the course :wink: