Gear ratio for best Zwift response in training mode (ERG).

(Mark H.) #1

I’m running a bike with the compact crankset (50/39, 11/25) on the Tacx Vortex smart.

50;15 is the optimal chain position and works well at lower power sections. Higher power segments tend to put me in to the uncomfortable high cadence.(115+)

50;11 puts lot of strain and unnecessary wear on the drive train but is the only way I can achieve reasonable wattage (group B) with normal or slightly elevated cadence (90-100).

300W requires 120rpm which may be ok for a short sprint but not an endurance ride. 130rpm is definitely uncomfortable for me.

According to the Zwift instructions we not supposed to shift in the ERG mode so it looks like I’m stuck in the lowest cog for now in order to maintain somewhat comfortable cadence.

Now, I would like to know how to approach group A training and complete higher wattage segments at reasonable cadence +/- 90rpm.

Please post your positive experience, what you have done and what worked for you. I like to find the solution to this “glitch” and I appreciate the team effort. J


(Bastiaan Gaillard [HIK - C]) #2

Hi Mark,

Using ERG mode, the trainer will keep your at the desired watts. You can always shift gears to play with your cadence. 

Groups like you mention (A, B, C, D & E) are not based on a higher wattage but on FTP and your weight. Functional Threshold Power (FTP) represents your ability to sustain the highest possible power output, depending on whether you’re a trained athlete or not. As a result 95% of the 20 minute average power is used to determine FTP. 

You can start two FTP test from the Zwift workouts module. When you have finished a FTP test you can calculate you watts/kg by dividing your body weight in kilograms to the average watts achieved in the FTP test.