ERG Mode and shifting

I’ve been using ERG mode on my Kickr for about eight months.  I started with 50x14 gearing, but about a month ago realized the I was having trouble maintaining 80rpm on flats and steep gradients (above 10%) were pushing my watts above 325 just to keep the cranks turning.  Not sure if this was due to automatic power increases by Zwift as I became more fit?  I’ve recently upshifted to 50x15 and seem to have found a happy medium. 

That being said, I tried Alpe du Zwift for the first time yesterday and really struggled on the early sections.  I shifted up to 50x17 and was able to handle the climb.  I averaged around 260w versus the 340+ in the harder gear.  Is this cheating?

I’m 51 and a large rider - 6’5" @ 225lbs.  I want to work hard to continue to improve but don’t want to injure myself by pushing super heavy gears at low rpm.  Would appreciate any advice.  Thanks

Hi Michael,

Yes, definitely don’t want to injure yourself. That’s would not be good.

It seems like you’ve been indoor training for a while. Have you done an FTP test recently to make sure your FTP is appropriate for your training workouts? 

If you’re using the appropriate FTP for your fitness level during your Zwift workouts, I suspect that there would be less risk of an injury. 


ERG mode is only used during workouts where your trainer forces you maintain a specific power level. You stay in one gear throughout the workout. If you change cadence the power output remains the same. Slow cadences will increase the resistance and higher cadences will reduce the resistance but the overall power output should be the same. Anything under 80 is usually considered grinding away and can be hard to maintain for lengthy periods whereas anything over 100 can be hard to maintain. 85 - 90 for many people is the optimum range.

In ERG mode you will feel a difference between using the small chainring vs the large chainring as using the large ring and a small cog on the back makes the flywheel spin faster. It gives it more inertia. You can momentarily ease off and not lose any flywheel speed however if you use the small chainring and a large cog on the back the flywheel speed is much slower. You quickly lose power if you ease off. Similar to climbing a hill. For me I find the small chainring and about the 15 on the back works best in ERG mode. Quieter as well as the flywheel speed is lower than using the large chainring and a small cog.

Where you do change gears is when riding Zwift normally or in an event. That’s when your smart trainer will change resistance based upon the terrain. Alpe du Zwift is a tough climb. If you run out of gears you can change the trainer difficulty in the settings. 50% is the default.

As mentioned, make sure your FTP is set correctly. If you do an ERG mode workout and your FTP is set too high the workout will be too hard.

I’ve only done routes on Zwift, so no workouts.  I’ve wrongly assumed all along that ERG mode was active… so I’ve only used the 50x14 or 15 gear on all rides. I checked and the trainer difficulty setting is at 50%, which I believe is the default.

I re-rode about half of Alpe du Zwift last evening using my 34 chain ring on the climb.  I was able to maintain 80-85 rpm but I didn’t really notice much difference between a 7-9% gradient and steeper sections of 13-14%.  This seemed odd to me, so I downshifted  several times.  This resulted in spikes in power for a few seconds but my wattage would quickly settle back down to the low 200s.  Overall, the climb felt a little too easy.

I think I will move the difficulty level to 100% and retry.  Does this make sense?

Be aware that the cheaper wheel on smart trainers can only simulate up to around a 7% gradient. They will just max out the resistance and steeper gradients won’t feel any different. Yeah, try changing the difficulty setting.

Thanks Nigel.  I’ve decided to try changing the difficulty setting based on feedback to the same thread in the General Discussion forum.  

Also, I have done several FTP tests on Zwift.  They are similar to tests that I’ve done on Trainer Road, so I’m pretty confident that I’m good there.