What is Power-To-Weight Ratio?

Garmin Edge 800 GPS is used to track power.One way to get faster in cycling is to improve your power-to-weight ratio.  It is also a great way to compare the abilities of two cyclists.  Power-to-weight ratio is the amount of power you can produce in watts divided by your weight in kilograms.

Power-To-Weight Ratio = Power (W) / Weight (kg)

Or, for people like me who measure their weight in lbs:

Power-To-Weight Ratio = Power (W) / [Weight (lbs) / 2.2)]

Let’s say there are two cyclists that are racing down the singletrack together and they approach a long climb.  Who will reach the top first?  Cyclist 1 has a functional threshold power (FTP) of 250 watts, while cyclist 2 has an FTP of 275 watts. (We will discuss FTP in future articles)  Based on this information alone, you might assume that cyclist 2 has the advantage.  However, this isn’t enough information to figure that out.

If I tell you that cyclist 1 only weighs 150 lb. while cyclist 2 weighs 175, then we can calculate who goes into the hill with the best chance of summiting it first.

P/W(cyclist 1) = 250 / (150/2.2) = 3.67

P/W(cyclist 2) = 275 / (175/2.2) = 3.45

You can see that the cyclist 1 has the advantage because even though he produces less power, he also has less weight to carry up the hill.  Ask yourself, would you be faster with or without a 50 lb. camelbak weighing you down?

Of course, there is a lot more to it than this simple example – like motivation, endurance, fatigue, steepness and length of the hill, etc. – but this gives a quick illustration about how both power and weight will affect your speed on the trail.

You can also use the power-to-weight ratio to measure your own changes in fitness over time and I am a great example of that.  In 2012, my FTP was 260 watts (this is an estimate based on performance because I did not own a power meter yet) and I weighed about 185 lb. mid-season.  By the championship race in 2013 my FTP was 290 and I weighed 160 lb.

P/W(2012) = 260 / (185/2.2) = 3.09

P/W(2013) = 290 / (160/2.2) = 3.98

The combination of increasing my power through targeted training and my weight-loss led to a 29 percent increase in my power-to-weight ratio.  Not only do the numbers say I should be faster, I can tell you I was actually faster – much faster.  I was setting personal records in almost every race during 2013.  Not only that, but I felt more confident too.  It’s amazing how much smaller the hills feel when you aren’t worrying about red-lining.  I wasn’t just surviving the hills anymore.  I was using the ascents to attack.

How Can You Increase Your Power-To-Weight Ratio?

There are two ways to increase your power-to-weight ratio.  The first is to increase your power through targeted training aimed at the needs of your specific event.  I say specific, because even if you’ve increased your maximum sustainable power for one hour that doesn’t necessarily mean that you have good power for sprinting or 12 hour events.  I recommend using a power meter for your training, so that you can measure your results and target your training.  I’ll be talking more about that in upcoming posts, so make sure you come back to quickdirt.com for more insight.

You can also work on decreasing weight – both on your bike and on your body.  For chunkier riders, losing body weight is a great way to increase speed – especially on hilly courses.  If you are a little overweight, then losing some pounds can lead to better health too.  Other advantages include cheaper grocery bills and long-term medical care as well.

I lost over 40 pounds between February and May of 2013 and I can tell you first hand that this large increase in my power-to-weight ratio made a huge difference in my speed.  I’m talking about going 10 to 15 minutes faster in a 90 minute to 2 hour race.

Shaving weight off your bike is a good idea if you have some obviously heavy components or accessories that you can remove or replace.  The downside of this option is that it can get expensive.  The lighter your bike gets the more costly it is to remove each additional pound from it.  If you have a 25 lb. bike, you could easily spend $500 – $1000 to replace your current components with lighter items and still only save a pound or two.  This will lead to a very small percentage increase in your P/W ratio.  However, in a very competitive situation a 1% increase might make the difference between first and second place.

The Final Dirt

The most important part of riding is to have fun.  However, if part of having fun for you is going fast, then I recommend looking for ways to increase your power-to-weight ratio.  Please come back to quickdirt.com in the future for more articles.  Let me know about your struggles to get faster.  If you have any questions leave them in the comment section and I may use them as the inspiration for other posts.

One resource that I recommend for learning more about power-to-weight ratio is Training and Racing with a Power Meter by Hunter Allen and Andrew Coggan PhD.

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