Reliable, dual-sided power measurement in off-road pedals
Larger and heavier than Shimano pedals
220g per pedal
If you want a pair of power-meter pedals that works for mountain biking or gravel riding with Shimano SPD cleats, the new Garmin Rally XC has proven to be a good option. I tested a pair for weeks on various gravel bikes and against three different power meters, and with a few caveats, I can recommend them.
The Rally XC pedals look like slightly larger versions of Shimano’s XT and XTR dual-sided pedals, which are widely regarded for their performance and durability. But the Rally XC pedals house power meters within each spindle, and deliver a host of power-measurement data.
Another cool thing about the Rally XC pedals is that you can swap the pedal bodies for two road models: the Rally RS for Shimano SPD-SL cleats and the Rally RK for Look Keo cleats (which is basically the Garmin Vector 3 configuration). The road pedal bodies are $199 for a pair. (See the Garmin Rally news story for more details.)
The Rally XC’s left/right balance and overall power numbers tracked very well in my testing with a fifth-generation Wahoo Kickr, a Shimano Dura-Ace meter, and a Quarq meter. After an average-power variation of more than 3 percent on the first three rides, the Rally XC’s numbers settled into less than 3 percent variation across various durations to the Kickr and Dura-Ace meters, which I have used and tested for long enough to believe in their reliability.
I can’t comment on the long-term durability due to only having ridden them for about three weeks, but I have been testing Garmin Vector pedals since their first iteration back in 2013 and can speak to the improvements made along the way.
Rally XC versus SRM X-Power
I also tested two pairs of SRM’s X-Power, which is the only competitor to the Rally XC as a pair of SPD-based power-meter pedals. Those I found to read high in their measurement (8-9 percent high compared to other meters) and left/right balance (sometimes as much as 10/90). But then, both sets ultimately stopped sending wattage signals. (I charged them, recalibrated with the X-Power app, and tried with four different Garmin and Wahoo head units, just to make sure.)
There are compromises made in order to get a robust power-measurement system inside a Shimano SPD pedal — namely weight and size. I weighed a Rally XC at 220g compared to a Shimano XT pedal at 170g. The X-Power pedal I weighed at 171g.
The form factor of the Rally XC is a bit chunky. The stack height — measured from the center of the pedal spindle to the cleat contact surface — is 13.5mm, compared to 8.4mm for a Shimano XTR. The X-Power stack height is virtually identical to Shimano.
Yet, I must note: The X-Powers read high, then stopped working. The Rally XCs are on a gravel test bike now, where I use them with confidence. I’ll take a few millimeters of stack and a few grams of rotating weight if that’s the price.
I hope my issues with the X-Power pedals were isolated and can be remedied. SRM created the original cycling power meter, dating way back to 1986, and the German company’s spider-based road power meters are rock solid. I used one for years as the primary comparative tool for new meters. That to say, I don’t want to blow off SRM. I sent both sets back to SRM so their test engineers could investigate, and will post a review after I get them back and can test them more.
Rally XC power measurement vs Kickr, Dura-Ace, Quarq, and Wahoo
In addition to using them as my one power meter for gravel riding, I did 8 days of comparative testing inside, simultaneously using a fifth-generation Wahoo Kickr and a dual-sided Shimano Dura-Ace power meter. I also did a couple of days of testing outside with a Quarq meter.
Group power-meter testing is like democracy; it ain’t perfect, but it’s the best system we have. I have ridden with power for more than 20 years and have comparatively tested meters as part of my job for more than ten years. And I’m here to tell you, you’re never going to see two power meters perfectly align. But if two meters can track within 2 or 3 percent of each other, then you can have decent confidence in both. If you have three or four meters all performing within a 1 to 2 percent variance across the range of critical power durations, you can have great confidence.
Power meters often have distinct personalities. I have found, for instance, that spider-based Quarq meters read higher than Wahoo Kickr smart trainers, and Shimano’s crank-based Dura-Ace meters read lower than Wahoo Kickrs. And this pattern is the case for multiple iterations of each, not just the three I used here for testing.
For testing, I use the same recording settings on the head units (1sec, not ‘smart’), and calibrate each unit before the ride. I tested in temperatures between 20 and 75 degrees.
One point of curiosity is the discrepancy between Garmin power meters and Tacx smart trainer power meters, which are now part of the Garmin family. I’ve tested three Tacx Neos, and while they offer my favorite ride feeling with vibration surface treatments and easy spin-up after coasting, the power always reads more than 4 percent lower than other meters. Garmin senior product manager Kenny Carlson attributes that to where the power is measured.
“We expect them to be different,” he said. “What [Tacx] is measuring is truth. We are going to have about a 3 percent loss through the drivetrain, and it can get worse if you have a dirty chain or are cross-chaining. We are looking at that, certainly on our radar to find a good solution.”
I believe that frictional losses in the drivetrain are real. To the tune of 4 percent or more? I don’t know. But I do know that smart trainers from Saris, Elite, and Wahoo match the readings from pedal-, crank-, and spindle-based meters at a much closer rate.
Rally XC performance in use
Since the power meter’s guts are inside the spindle, you use a pedal wrench and not an 8mm Allen to put the pedals on and take them off. Spinning the cranks wakes up the pedals for calibration via your bike computer. Once everything is connected and calibrated, the pedals have a second or so delay in sending power when you start your ride. But once activated, there is no delay after coasting or traffic stops.
Clipping in and out feels like Shimano to me. There are 12 steps of tension adjustment, and the pedals come out of the box in the middle setting. Using the X-Powers at the factory tension setting on the Spirit World 100 course, I popped out a few times leaning the bike on washboard corners or once hopping a cattle grate. I clearly needed to tighten them down! With the Rally XCs, I have not yet unclipped unintentionally.
The vain part of me wishes I could feel the difference in stack height from Shimano to Garmin. But alas, swapping between Shimano, SRM, and Garmin on gravel test bikes on rough roads… I could not tell a difference. Now visually, sure, you can see a difference; they are chunky monkeys.
Unlike Garmin, I did not mount a pair of XCs on a mechanical test apparatus to repeatedly smash them into a cinder block. I just used and abused them like normal gravel pedals, occasionally striking a rock and sometimes kicking them to shed packed mud or snow from my cleats.
I have not yet exhausted the four little batteries, which Garmin claims will offer 120 hours of use. Replacing batteries on Garmin’s pedal system is fairly easy; I’ve found that using a magnet makes getting the second battery out easier. On my test Vector 3 set, the battery housing compartment failed after a year or so, which is something Garmin addressed with the Rally system (and also in replacement parts for the Vector 3). Also, having metal threads instead of the Vector’s plastic threads is surely a good thing.
Rally XC bottom line: A great solution for gravel riders and mountain bikers
My friend Tess recently texted, asking if good power-meter pedals existed that she could use to swap between gravel and mountain bikes. Well, Tess, yes; now they do. The Garmin Rally XC pedals, while slightly larger than the Shimano SPD pedals they imitate, work quite well as both off-road SPD pedals and as a dual-sided power meter.