Powermeters and Pedal Extenders


I have been having an ongoing knee issue, so I decided this past December to go in for Bike Fit Tune ups on my road, gravel, and “trainer” bike. I decided to start with the trainer bike as it was the one I was using most frequently given the weather in the Northeast at this time of year. We made some adjustments, which unfortunately resolved the knee issue, but caused issues in adjacent soft tissue. So, I went back in for another adjustment this past week. Too soon to tell whether these are the correct adjustments, early indications are promising.

One of the changes made was to add 19mm pedal extenders to help my knees track better. This is all fine for the trainer bike, as I don’t have a power meter. I source the power from whatever smart trainer I have the bike on, currently a Kick’r Move.

My concern, my road and gravel bikes are using dual side Garmin Rallys (RK200 for the road, and XC200 for the gravel). After a discussion with Garmin support, I know that pedal extenders are not supported for two reasons (1) it will block the antenna/transmitter that is at the end of the spindle; (2) Could potentially lead to misleading power numbers because of some changes to how the strain gauge is deflected.

I am not very clear on how an extender will affect the measurement. Which leads to my next question.

I reached out to several power meter manufacturers (Wahoo Speedplay, Favero Assioma, Stages, SRAM/Quarq. All provided the same response, pedal extenders are not supported, they will import the values being reported. Leaving out Speedplay and Favero, how does a pedal extender affect the values being reported by a crank arm, spider, or spindle-based power meter?



With the Stages crank-arm power meters, I can tell you that they over-read when you simply apply more force to the outside of the pedal farthest from the crank arm. If I pedal like a waddling duck the numbers go up. Not by a huge amount, and I wouldn’t care to pedal that way, but it’s pretty obvious when it’s happening. Anything that would allow you to shift the cleats laterally could do the same.

Its odd that Speedplay did not advise that they support different spindle/axle lengths which could give the same effect of moving the pedal laterally (and Speedplay cleats can also be positioned laterally on the shoe in addition to the axle length change)

I asked them specifically about the Speedplay POWRLINK Zero Dual pedals. This was their response:

The tightly controlled algorithm Wahoo uses in our POWRLINK Zero pedals does not currently account for pedal extenders. As such, the use of extenders with the POWRLINK Zero would likely skew power numbers in unexpected ways. Wahoo does not recommend the use of pedal extenders with the POWRLINK Zero pedals.

I had pedal extenders since my toes point outwards and when I had a bike fit he corrected my cleat position (to help my knees track in a vertical line and stop moving towards and away from the bike) and this led to my heel hitting the crank. He put pedal extenders on to fix that problem. When I bought assiomas they have a longer spindle anyway to make room for the battery pod and this was enough for me to ditch the pedal extenders.

Do the pedal extenders just increase your Q angle?
If so,the Assioma Shi (Shimano) already have an increased Q angle compared to the others.

Not an unexpected response, given that original Speedplay model pedals were oft found attractive because they were so fittable for riders, coming in 2-3 different spindle lengths, while the Powrlinks only ever (for some reason) were engineered for a single Q factor (55m) an no others.

On my trainer bike, the q-factor of the Keo Classic 3 pedals are 53mm. The extenders added another 19mm, to bring the total q-factor to 72mm. The Garmins RK200 and the XC200 both have q-factors of 53mm.

I will need two sets, one for road and one for gravel/mtb. When I looked at the Favero, the Assioma Duo has a q-factor of 54 and the Duo-Shi is 64/65. They are still not close to the 72mm that I am currently at. Could the Duo-Shi work? I would have to check with the bike fitter. However, there are three other issues: (1) they are rechargeable. It is easy to carry spare batteries with me for the Garmins. (2) Even if the Duo-Shi would work I would still need to purchase the pedal bodies and switch from Look to Shimano SPD-SL cleats. (3) It doesn’t resolve the gravel/mtb SPD pedals.

I have the duo shi’s. If you do go that route note that you may also need a tool to get the Shimano pedals apart, they are not much (I got one for $15 CAD off Amazon). As for batteries I guess that is personal preference, I prefer rechargeable (don’t have to buy batteries, better for the environment). I probably charge mine monthly through habit and I would guess I do maybe 40 hours riding a month. I think I did get a low battery warning once on my head unit on a ride and when I got home there was still 20% left or something so wouldn’t have run out on my ride.

As for you having too many bikes I can’t help there unless you want to give me some of them :wink:

OK, I had assumed the Powerlinks also supported the same spindles as the non-power versions.