How much FTP increase to increase mph outside

This could be an unanswerable question, but here goes. How much of an FTP increase, either numerical value or percentage increase, does it take to increase a mile per hour outside? This would be on a road bike or Triathlon bike. I currently have an FTP of 205 and generally average about 18 mph on a 50 mile ride.

You can start by using a couple of the common “calculators” for estimating speed, power and such:

As you can see, you need to know a number of data points to do much of an estimate.

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Do you want to increase from 10mph to 11mph, or from 25mph to 26mph, one will take ALOT more watts than the other…


Holy geez, Ok I have to go find all my data and start plugging in numbers

I was wanting to go from 18 to 19 and 19 to 20, and so on. Just curious while I suffer in my basement.

None, get more aero. I am about 1mph faster or more but about 10w down now (circa 25w at the start of the season).


If you have a power meter on your bike, you could also do a short, flat loop or out and back (to neutralize wind), holding 18 mph and then completing it at 19 mph, to see how much extra power is required to boost speed by 1 mph. Then maybe apply that percentage increase to your FTP. The models above I’m sure would be more precise, but if you aren’t after precision (and don’t have your CdA handy), but rather just need a target to aim at, that may suffice. And while you train to build FTP over time, you could also work on holding an aerodynamic position. If you ride in the aero hoods position for example, you certainly won’t need as much power increase.

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The number of watts it will take to go an extra mph faster is bigger the faster you are already going. So the answer depends on how fast you’re going.

There is also a lot of variation between people with how aerodynamic you are. Check out the thread here where people posted the average power they needed to get a sub hour 40k TT. Highly variable answers, related to highly variable drag coefficients between people and bikes. So the answer depends on how aero you are.

For me personally: 210-220w will get me to 20mph. 200w will get me to about 19mph.

People’s ability to sustain power outputs as a percentage of FTP are highly variable - FTP is only a single metric out of many on how to measure performance. I can do 65-70% of FTP for >8h. Some struggle to do this for 2h.

So the FTP you need to go an extra mph faster? Unanswerable. At your speeds, you probably need to go an extra 10-20w to your current power output. And you can probably do that without even increasing your FTP.

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I think you should start with making yourself more aero. Since you are posting here, I assume you do TR rides. So when doing endurance workouts, try to extend your time in an aero position (aero hoods or in the drops). You need to work on that, it’ll take some time. And it’ll be uncomfortable. One trick I use is to position my fans so I get optimal cooling in the aero position and suboptimal cooling when more relaxed. That nudge works.

Another big one is clothes: buy tight-fitting clothes, that has a much, much, much bigger impact than an aero frame or deeper wheels.

And then get a bike fit to make sure you are comfortable on the bike.

Lastly, one thing about speed is that it depends on a whole host of other variables. Apart from the obvious, wind, your clothing and temperature will have a huge impact. (Here, I mean that warmer clothing tends to be baggier and thus, less aero.)

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The simple answer is a little too simple but the it’s that power approximately varies with the cube of speed. 19 mph is 5.6% faster than 18 mph so, all other things equal, you’d need about 17% more power.

The real moral of this story is that you can get faster either by increasing your power or reducing your drag – or, most importantly, both. Doing both is allowed.