Pacing a Triathlon Bike Leg with Power

March 4th, 2018

Warning – this article is quite long! However, it really is worth reading all the way through if you’re interested in power meter pacing for triathlon. This is a simple summary. If you’re further interested in the subject, I’d highly recommend the book ‘Triathlon 2.0’ by Jim Vance. He takes an in depth look at the science behind racing your perfect race, and it’s a great resource for data driven athletes.

To make the most of the website mentioned in the article – – you’ll need a GPX file of the new Ironman route. I’ve uploaded it here:

Power meters have revolutionised the cycling and triathlon worlds. They allow riders to understand exactly how much effort they’re putting in on the bike, regardless of gradient, weather conditions, or any other variable they might encounter. With a little bit of knowledge, this information can help you pace a triathlon bike leg perfectly, leaving you with enough energy to execute the run leg perfectly. Look closely, and you’ll see that most pros and high performing amateurs use power data throughout their races in order to measure their efforts and squeeze out every last drop of performance.

Before we Start – Some Key Information

Functional Threshold Power:
If you’ve been training for a while, you’ll most likely have heard of Functional Threshold Power, or FTP. In simple terms, this is the power level, measured in watts, that a rider can sustain for an hour-long ride when pushed to their limits. A common test to calculate an athlete’s FTP is to conduct a twenty-minute, all-out effort on a turbo trainer after a suitable warm-up. Take the average power for those twenty minutes and multiply it by 0.95. The figure you’re left with – 95% of the average power you can hold for twenty minutes – is your FTP. Make sure you know this, and that the test was conducted with the same power meter you’ll be using during your races.

Normalised Power:
Imagine you set out on a three-hour training ride. Over those three hours, your average power was 200 watts. This will give you an idea of how hard you pushed – just compare the 200 watt average to your FTP. The greater it is a percentage of your FTP, the tougher the ride. However, average power doesn’t tell the whole story. There is a difference between a three-hour ride in which an athlete consistently holds 200 watts, and one in which the rider mixes up high intensity bursts of 400 watts for a minute at a time, with periods of cruising along at 100 watts. __The small bursts of power, well above your FTP, cause greater physical exertion than a constant, steady-state effort.__ Normalised power takes this into account. The greater the variation in the watts you push in order to generate the average power for the ride, the higher your normalised power will be. This normalised power, which you’ll find in Training Peaks or Strava, gives you a more accurate idea of your effort over a long ride than average power. __Normalised power is the key variable to pay attention to when pacing a triathlon bike leg__. Now here’s the really useful point to take away: pair up a power meter and a bike computer, and you can view the normalised power for a bike ride __whilst you’re on the bike__. This is going to allow us to pace our triathlon bike legs perfectly. __ADVICE: NORMALISED POWER SHOULD BE ONE OF THE DATA SCREENS YOU DISPLAY ON YOUR GARMIN.__

Setting a Power Target for your Bike Leg

Triathlon is one sport – not three individual events combined. There’s no use pushing your hardest on the bike if you have to walk when you ought to be running. But equally, you don’t want to go to easy on the bike, or it’ll cost you valuable time. So how do we figure out how hard we should push? For the purpose of this exercise, I’ll assume you’re racing an Ironman. That’s a 112-mile bike leg, followed by 26.2 miles of running.

If we look at the results from the Ironman World Championship, and examine the power data from the best athletes, we see a pretty consistent pattern. The pros seem to have a target intensity factor (IF) for their ride of around 0.8. What does this mean? It means they ride the bike leg with a normalised power of 80% of their FTP. If their IF was 0.85, that’d 85%. It is was 0.45, it’d be 45%. But 0.8 is generally what the pros aim for. That leaves them just enough in the tank to run a great marathon, but is hard enough to achieve fantastic bike splits.

Now, for us mere amateurs, 80% of FTP is rather unrealistic – though if you’re seriously considering qualifying for Kona, it might be your aim to ride at this intensity. Brian Fogarty, a serious amateur on the cusp of going pro, rides right up at this level. If you’re not quite at that level, here’s a general guide:

Your normalised power for an Ironman bike leg should be between 60% and 80% of FTP.

The better your physical condition, and your strength on the bike, the higher up that scale you should be. If you’re new to triathlon, and not used to pushing hard for long distances, you might set your targets at the lower end. If you’ve got years of cycling to fall back on, perhaps 75% should be your aim. Discovering what suits you best will involve experimentation – it’ll be a personal choice that only you can really know. The marathon of an Ironman isn’t an experience you’ll get to try many times, so I’d err on the side of caution if you’re not sure. It’s better to be able to up the pace in the final 10k of the marathon than have to slow to a crawl. Disclaimer: I have not managed the first – but for this I’ll be using a power meter on the bike leg for the first time and hope to do so!

Steady State Riding, or Bursts of Power?

You might be asking yourself: “Should I aim to ride the whole course at a steady wattage, or should I push harder on some parts, and relax on others?” It’s a good question to ask. Thankfully, people much cleverer than me have answered. The chief science officer at Training Peaks runs the website []( "") . It’s an absolutely wonderful site. Input your weight, bike type, FTP, desired intensity factor (e.g. 75% of FTP), and the bike course you’re going to ride, and it will churn out the best way to ride the course to finish it in the quickest time possible. It’s an incredible resource.

- It will tell you exactly how many watts to push on each section
- It will predict your finishing time should you follow the plan
- You can play with the variables to see how changing them will affect your ride
- If you’re into your data, you’re going to love this site. What’s more, you generate a few free race plans, meaning you could plan out your Ironman UK bike leg without paying a penny.

One of the key take aways from the site is that you’re better pushing harder on hills, and relaxing on downhills in order to reach your normalised power target. However, you should never go too far above your targeted normalised power at any one point. Let’s say you have an FTP of around 305 and would like your normalised power to be 75% of that figure at the end of the course. That should leave you just about enough energy to run the marathon at a decent pace without walking (so long as your run training has gone well). Input the Ironman UK course and these details, and it’ll generate a plan for the race. You can see it below (305 watts in a highly optimistic aim I have by July – not an accurate figure for my current FTP).

On the graph above, the thin blue line shows elevation. You can see Sheephouse Lane appearing twice (the two big peaks) and Hunters Hill following the long descent. The orange line shows estimated speed in the aero position on a TT bike. The light blue / grey bars in the background __show exactly what watts I ought to push on each part of the course to ride the quickest leg possible__. For example, I should push 299 watts at the top of Sheephouse Lane. You know the bit – where you turn the corner and gets really steep on the straight section of road. 299 watts. The most I should push for the whole leg. Note: that’s still under my (idealised) FTP. On Hunter’s Hill, I should push 281. But there are descents where I should only push 155 watts – about 50% of FTP!

If I managed to ride the bike leg exactly as suggested, and my FTP really was 305 watts at 68Kg (again – highly optimistic), Best Bike Split predicts a 5hr 33 bike leg might be possible. Of course, this depends on perfect weather conditions, spotless cornering, and being on the aero bars for the whole ride. But the key is the power targets – that’s what to pay attention to.

Finally, you might be asking, “How can I realistically follow a power plan for upwards of 5, 6 ot 7 hours? How do I remember it all?” Here’s my suggestion. On your top tube, or on your between-the-arms aero water bottle, tape a piece of paper with the following information on it:

- Normalised Power Target:
- Max Power Allowed:
- Sheephouse:
- Hunters:
- Descents:
- Flats:

For me, they’re the key bits of information. Make sure you never go above your max power target. Make sure you chill out (but not too much on the descents). Make sure your normalised power rating is always somewhere around the target – particularly after the second ascent of Sheephouse.

This might seem like a lot of information, but get used to using it in training, and you’ll be able to pace yourself to your best ever Ironman run. Because that’s where the race is made – the marathon.