By CTS Coaches Nick White and Jim Rutberg
Two of the Ironman races in the US feature relatively flat and fast courses, and the terrain can have a significant impact on your strategy on the bike. Neither Ironman Florida nor Ironman Arizona have hills to match those in Lake Placid, Wisconsin, or St. George. Instead, there are long stretches of flat roads. Ironman Arizona’s bike course even features an extended stretch that’s a very slight – almost imperceptible – downhill. In these conditions, momentum is key.
Over the years you’ve heard CTS coaches and many other coaches talking about riding with a high cadence. Generally speaking, a high (90+) cadence is beneficial because it allows you to you less force during each pedal stroke. Remember, power is the product of angular velocity (cadence) and force. You can produce 250 watts of power pedaling faster or pedaling slower. But when you pedal slower, you have to produce more force with each pedal stroke in order to produce those 250 watts. When you pedal more quickly, each pedal stroke is less forceful, and the muscles in your legs don’t fatigue as quickly.
The other reason that high-cadence pedaling is beneficial is that it helps you adjust to rapidly-changing conditions, like hills and corners. Accelerating a bigger gear is more difficult than increasing your cadence – and hence your speed – in a smaller gear. This is a very easy concept to test: slow down for a sharp corner and try to accelerate out of it in a big gear (say 53×14 or 50×13). Then repeat the same corner and accelerate out of it in a smaller gear (say 53×17 or 50×16). In the smaller gear you can get up to speed more quickly and you won't place as heavy a load on your legs. Similarly, on rolling hills you can maintain an optimal power output more easily while riding in smaller gears because you can fine-tune your gearing and cadence, whereas you get bogged down in bigger gears and have to struggle against heavy resistance.
But while high-cadence pedaling is beneficial in most cycling situations, there are times when you want to roll a big gear with a relatively low cadence – and Ironman Florida and Arizona are two of those places. On long, flat stretches of open road, you want to get your bike up to a high speed by pedaling with a high cadence (90-100rpm) as you accelerate through your gears. But once you get to a high speed, you should shift into a harder gear and bring your cadence down (80-85rpm, but no lower than 80rpm). On flat ground, in tailwinds, and on slight downhills (like the long on in Ironman Arizona), once you’re up to speed you can maintain it without having to add a tremendous amount of additional power.
The key is to maintain your momentum. You want to use just enough power to avoid slowing down. And because high-cadence pedaling is associated with a higher heart rate and respiration rate, you’ll also see that your average heart rate comes down while you’re rolling a big gear. From an economy standpoint, this is a good thing!
To maximize the positive impact that rolling a big gear can have on your Ironman performance, stay in your aero tuck as much as possible and consciously think about maintaining or adding to your momentum. This means you want to use your brakes as infrequently as possible. Obviously you need to use your brakes for safety, but in all other instances you want to avoid scrubbing speed unless absolutely necessary. Speed lost means extra energy expenditure from having to accelerate, and the more times you brake and accelerate, the faster you fatigue.
As you near the end of the bike leg in a flat Ironman like Florida or Arizona, you will want to increase your cadence and ride a slightly smaller gear in order to get ready for the run. Your power output can stay the same, but bringing your cadence up to 90-100 will help you transition to the run with a higher turnover and snappier stride.
Bonus tip: Since most of us ride local group rides or train with a small pack of other cyclists or triathletes, it’s important to realize that low-cadence, big-gear riding has a place in group rides as well. When you’re sitting in the back of the paceline or the middle of the group, you can bring your heart rate and power output way down by shifting into a big gear. Because of the draft, you’ll only need a minimal amount of power to maintain your momentum and stay on the wheel ahead of you. It’s a great way to conserve energy when the group is just cruising along on flat ground.
Nick White is a Premier Coach with Carmichael Training Systems. He has coached Ironman World Champion Craig Alexander and Ironman St. George winner Heather Wurtele, and he works out of the CTS Tucson Training Center. Jim Rutberg is a Pro Coach with CTS and co-author of 7 books with Chris Carmichael, including "The Time-Crunched Triathlete".