How many Watts do you need to break 20 minutes for ten miles?

30 miles per hour is the holy grail of time trials. It’s the average speed required to break 20 minutes for a ten mile time trial and 50 minutes for a 25. These are marks held in high esteem by riders up and down the country, but how many watts do you need (or how aero do you need to be) in order to hit this mark?

A myWindsock experiment

If you head to the myWindsock app and play with the input variables on a forecast for a given course, you’re able to see the kind of power and cda values required to achieve a given time.

The course used in our forecast is the national 10 on 3rd September 2023 at 7:00am and you can see the forecast by clicking on the link. Of course, the forecast is likely to change between now and race day but these numbers should give you a rough idea of what’s required on that course if you’re planning to head there and crack 20 minutes.

Take a look at the course forecast by clicking here!

CdA vs Power – what do I need to go sub 20?

Time trial performance can be boiled down to two key numbers – your cda (how aero you are) and your power (how hard you’re going). Obviously each of these can further be broken down into constituent components but one simple fact remains true – you’ll go fast if you have a combination of good power and you are aerodynamic, this is news to nobody. There is a little bit of a trade off between aerodynamics and power – which you can read about here.

This image shows the combination of aerodynamics and power needed in order to break 20 minutes on the National 10 course this year. The average time trialist in the UK will break 30mph with a cda of just a little more than 0.185, a very low number!

There are a few key takeaways from this graph…

  • The average rider going under 20 minutes is doing 340W, this isn’t a huge amount of power and tells us that British riders are super aerodynamic.
  • If your cda is 0.2 (the general marker for ‘good’) then you’ll need 360W to break 20 minutes, again very strong but an achievable number for many riders in Britain.
  • At Remco Evenepoel’s reported cda, it would require 320W for him to ride at 30mph on this course, given that he’s capable of around 80W more than this over 20 minutes in the TT bars it works as a stark illustration of just how good world class time trialists are. 

How to work out your CdA and use myWindsock to plan your race

If you want to know your cda, you can carry out a field test using myWindsock. This can be done by the methods explained in this article.

Once you know your cda, you can head to the forecast here and work out how many watts it will take to achieve your target time. This course, I suspect, will crown a national champion that gets close to 18 minutes and there will be plenty of riders that ride under 19 here. For reference, a 19 minute clocking requires a rider to average around 400W with a cda of 0.18 – these numbers sound pretty crazy but there’s probably 15-20 guys that can hit these numbers in the UK.

You can take control of your race and remove uncertainty by signing up to myWindsock here.