Wahoo Kickr Climb Zwift “Trainer Difficulty” Wheelbase Hack

If you are not familiar with the ins and outs of Zwift’s “Trainer Difficulty Setting” I suggest you read this excellent Zwift Insider piece as a primer before continuing.

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The Wahoo Kickr Climb at first blush does not have much adjustability of operation because of the way it receives signals from the Kickr trainer. This poses a problem for anyone who has their trainer difficulty setting at less than 100% which is the majority of Zwifters–especially those who race.

The slope the Climb produces is identical to the slope in game multiplied by the “trainer difficulty setting”. Therefore, if you have the slider at 50% then the Climb will only move to 5% when on a 10% grade in game.

Most riders have the difficulty set lower to reduce the frequency/necessity of shifting and also to not spin out/be able to provide power on descents. Most racers I know compete with their trainer difficulty settings in the range of 10% to 20%. So when running difficulty at 10% the Climb would go to 0.3% on a 3.0% grade and only 2.0% on a 20.0% grade. There is no reason in racing or otherwise that I can think of that a user would want the Climb to not simulate the actual slope regardless of trainer difficulty. For me the two biggest selling points of the Climb are the correct ergonomic simulation of body and bike position on gradients and increased immersiveness of the simulation.

I called Wahoo and expressed this concern but they said there was currently no way around the issue because Zwift simply sends the slope/gradient to the trainer already modified by the “trainer difficulty setting”. The trainer then simply relays this number to the Climb. They also said others had contacted them with the same issue but that there was not a fix in the works yet. I suggested that in the future they add a field in the Climb config for the user to enter a multiplier to correct for the trainer difficulty setting.

Then I realized that they had already accidentally done this in the settings, but for an entirely different reason!

The solution: WHEELBASE!

In the Wahoo Fitness app under the Kickr configuration (once you have paired your Climb) there is a field for you to enter your wheelbase. A bike with a shorter wheelbase will require slightly less travel from the Climb to produce the same slope than a longer bike. Thankfully the engineers/coders did not limit the range for this field! Therefore it can be used as the “correct for trainer difficulty multiplier” and wheelbase simultaneously. This makes me VERY happy!

Three steps:

1. Look up your wheelbase (mine is about 1000mm)
2. Divide your wheelbase by your trainer difficulty setting from the perfs.xml file
3. Put the result in the wheelbase field

So for my bike and setting it shakes out like this:

1. 1000mm
2. My difficulty is set at 20% so : 1000mm / 0.20 = 5000mm
3. Enter 5000mm in the “wheelbase field” in the Wahoo fitness app Kickr setting

Now the climb will simulate the full slope (accurately enough for our purposes) regardless of the trainer difficulty setting!! You just need to remember to adjust this number if you ever change you trainer difficulty setting in Zwift.

Notes:

Although the slider in Zwift settings makes this setting seem analog, you can see (and alter) the exact number for this setting in the “prefs.xml” file in your Documents/Zwift folder.

In the xml file the line is <TRAINER_EFFECT>. If you have only adjusted the slider in game you are likely to find the line with a numerical value like this: <TRAINER_EFFECT>0.48656234</TRAINER_EFFECT>. This was with setting the slider roughly in the middle – hence the number is close to .5 though not exact. You can edit the number in the file (it will move the slider automatically in the settings) and keep this number until you touch the slider in game or edit the prefs file again.