4iiii dual crank issue...I'm very disappointed

So, I sent my Shimano XT crank to 4iii two months ago to have them install power meters. There were none in stock, so I sprang for the $500. Yes, expensive, but I really needed them, and I wasn’t sure when they’d come back into stock, you know, with the pandemic and all. I get them back, and they work great. I discover I have a 49/51 L/R imbalance. Nice to know. 12 rides later all of a sudden it goes to 40/60. And it’s not really an imbalance, the left crack is reading the normal power, it’s the right side all of a sudden reading 50% more power.

So…I contact 4iii support, (no phone available, just email.) I’m told to reset the crank. Great, fix works, back to 49/51. I was told a firmware update must have been interrupted and that’s what threw off the right side. That made no sense to me, but hey, the fix worked.

12 rides later….the right side is messed up again. 40/60, and again, the left pedal reads normal, it’s the right one that is reading 50% greater than normal. i contact support, and I am asked to record a ride using the 4iii app, (not my Fenix 3) and send the .fit file back to them. The .fit file shows the same screwy right pedal power. The email I get back from them is pasted below. First, the reply shows that they have no understanding that the problem is not a simple imbalance, but rather the right pedal is all of a sudden reading 50% more power. Second, they apparently want me to pay for the shipping back. To say I am pissed is an understatement.

I sent an email reply asking for them to pay for shipping. I’ll let you know how it works out.

edit. p.s. Forgot to mention, I reset the crank again, and it’s back to normal power.

You will always see an imbalance of strength between legs; very rarely will you ever see a 50/50 split. I’m a former speed skater so my balance is around 40/60 but I already know that so I use a scale factor to balance it out. Now that being said, if you feel that this powermeter needs replacement, please complete the Return Merchandise Authorization (RMA) form attached to this link:

4iiii RMA Form

Once you receive the RMA number, please ship us your crank arm. You will also receive information on how to track your repair. It should take roughly 5-10 business days and 3-4 business days for shipping it back to you.

We recommend sending it via courier with a tracking number. Be sure to include your return address and copy of the bill of sale. Once the repair is complete, we will ship it back to you with a tracking number.

They should step up to the plate and provide you with a return label.

Some companies have lenient policies that get abused. Not saying that’s the case here, but it’s a possible explanation. Then again, there are also some companies run by absolute bean counters.

Either way, I hope they fix it for you.

PSA: When I had a problem with a Stages Ultegra PM, they were able to diagnose a problem from a calibration and a couple photos. They sent me a new PM and a return label for the bad one. Not trying to rub salt in the wound. Just mentioning this because a lot of folks recommend 4iiii over Stages, but this just goes to show that nobody’s perfect and both companies have their pros/cons.

Well, after i complained, they did offer a paid return label. I was also contacted by a different person at the company, and they now understood the complaint and that it wasn’t that my right leg was 50% stronger than my left…sometimes. I should edit my OP. The funkiness in the meter was from the get go. My very first ride showed 50% higher right power. I then reset it as instructed, and it worked ok for another 12 rides, until it flipped out again. My point is that the meter was defective on arrival. It would really help 4iiii if they offered phone support. A lot of angst (mine!) could have been avoided.