A Smart trainer like the Wahoo KICKR includes a load-restricted mode called Erg Mode. This mode will set your trainer's resistance for you rather than leaving that responsibility on your shoulders.
Riding in Erg mode is a little like loosening your grip on the reins of the horse you're riding. You basically give control to your trainer/horse and simply ride. In this mode, smart trainers constantly adjust the resistance to match TrainerRoad's Target Power.
Each rider's Target Power is based on your profile's FTP and Erg mode will set your trainer's resistance based solely on this number. When you change that number following an FTP test, your smart trainer will adjust your intervals accordingly.
For more specifics on assessing your FTP on a smart trainer, see our related article, How To Test With the Ramp Test.
While an exceptionally effective way to train, there's a bit of a learning curve to Erg riding so here's an explanation of what Erg mode is all about along with a number of tips & suggestions to help you get the most out of your part-time ergometer.
Erg Mode Basics
Erg mode sets your Target Power regardless of your cadence or your gearing selection. You can turn a huge gear at 60rpm with a Target Power of 80% FTP and you'll face the same resistance as you would using a tiny gear at 100rpm even though your speed will be vastly different.
Let's say you have a 200w FTP and you're riding an 80% interval with a 100rpm cadence. Any TrainerRoad-supported smart trainer with Erg mode, e.g. KICKR or CompuTrainer, will set the resistance to 160w as you spin steadily.
Say your gear selection yields 20mph but you then change your spin to 100rpm but remain in that same gear. Your smart trainer will readjust in order to return the resistance to 160 watts after a couple seconds - some trainers adjust more quickly than others.
Even though your speed is now 24mph, you're still only working at 160 watts. Even if you change your spin to 70rpm, the same thing happens - a quick readjustment to keep you at 160w even though you're now pedaling at 14mph. All of this happens in that one gear you've been in the entire time.
Simply find a gear that keeps the noise down, leaves your chain pretty straight (no sense increasing wear on your drivetrain with a crossed chain) and forget about shifting, even when you move in & out of the saddle.
Nutshell: Shifting is a thing of the past when you use ERG mode.
Which brings us to a finer point of Erg mode riding. When you move from seated to standing, simply slow your spin & rise - no shifting. When you return to the saddle, try to wind your legs up a little bit as you take your seat and get your cadence back where you like it - again, no shifting.
This is a practiced skill and might take some time, but it prevents big surges & drops in power when you change positions. In both instances, the power is going to rise or fall a bit for a couple of seconds but will stabilize rather promptly.
Here's the catch though, and this applies to both saddle transitions and long periods of time in or out of the saddle: the more often you change your cadence, the more often your smart trainer has to readjust the resistance and the less "on target" your interval will be & the less accurate your end-of-interval metrics will be as well.
This goes for any changes in cadence. When you speed up, the trainer has to make an adjustment to your new cadence, the same when you slow down. So when you alter your cadence, try to resist the temptation to shift; rather, wait for a couple of seconds and watch as your power comes right back in line with where you need it, i.e. your Target Power.
Nutshell: Don't shift, don't change your cadence a lot, and have a bit of patience & faith in the technology.
Sometimes when riding low-wattage intervals, riders may come into contact with what we call the "wattage floor" - essentially the trainer's lower mechanical limit. When this happens, riders may not hit their target watts for recovery intervals since the target power is beneath the "wattage floor" of the trainer. In other words, the number of watts it takes to turn the pedals is higher than the target power.
When you come into contact with the wattage floor, it will often appear as though your trainer is "floating" above the target power. Each trainer is slightly different, but most commonly riders will encounter the wattage floor when riding recover intervals below 100 watts.
The good news is that the wattage floor is usually pretty easy to avoid. If you find that you're running into the wattage floor, try shifting into an easier gear. The trainer's wattage floor is lower when using easy gearing combinations, so down-shifting should allow you to reach those low power targets.
Smooth Power Output
One advantage of smart trainers is how they keep your power exceptionally smooth. Check out the distinct difference in how closely Target Power matches Actual Power between the same workout done on a regular trainer (top) and on a smart trainer in Erg mode (bottom).
Low Cadence Work
It's also worth mentioning that during slow-force workouts, i.e. efforts where you're shooting for a really low cadence, say 50-60rpm, a big gear is necessary to hit higher watts with a slow, muscular spin. This is especially true on CompuTrainers but may not be an issue on more newly designed smart trainers.
How Does ERG Mode Work in a Free Ride?
Erg mode doesn't work well in a Free Ride because there is no power target to hold your trainer to. Instead, your trainer will automatically switch into Resistance mode.
We hope this helps you blow through the Erg mode learning curve a bit quicker than you might have without this advice. Feel free to contact our support team via live chat or with an email at firstname.lastname@example.org.