Can a loose and creaking BB affect power readings?

Hi, long time reader first time poster.

I have been dealing with two separate problems on my mtb and looking for solutions.
First is a creaking bottom bracket caused by a too large BB hole on the drive side.
Second is a Quarq powermeter reading increasingly higher values alongside creaking.

When I put back in the bottom bracket and calibrate the Quarq with weights all is well for a while. After a while BB starts migrating towards crank and creaking. With that powermeter starts reading high. I do a stomp test with weights and set the slope. Bu readings and creaking get higher and higher until I have to take it apart and start from the beginning. Rinse, repeat.

Frame is PF BB92, Boost, GXP crank. Round chainrings. I have other powermeters which I test with same weights and they are spot on.
I am planning to get rid of the Quarq and get pedal based PMs but I have to fix the creaking anyway. So if a loose and moving about BB can throw the powermeter readings off I might get away with just fixing the BB issue.
On that front it is either a one piece BB like bbinfinite or industrial glue :slight_smile:

If the hole is too big, isn’t this a warranty issue? I had a frame replaced for this issue.

Check out some of Hambini’s YouTube rants about shoddy frame making - this is one of the things he sometimes finds. Warranty it.

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Frame is too old and beaten up for a warranty. Should have measured it from day 1.

I am aware that cycling industry is not capable of making round holes. Does it cause more than just creaking though?

Depending on the Quarq loose chainring bolts (even just one) can contribute to rising power over time and/or invalid power numbers.

Who makes the frame? I spent two years chasing a creak on a S-Works before it was warrantied. If it has a lifetime warranty you may not be out of luck. After all, that is a manufacturing defect.

Any yeah, the Hambini video on this is interesting!

We eliminated all these other factors. All bolts are torqued correctly.

One other observation is it starts to go high on the left side first. When I am doing the stomp test left side produces higher torque numbers.

Do you make a note of the zero offset number when you calibrate the Quarq through your headhunt. I believe if it jumps more than 50 points then that indicates there could be an issue.

Correct per the manual:

Power Measurement & Zero Offset Issues
• The power meter is giving very high or low power readings.
• The zero offset value is greater than +/-1500.
• The zero offset value is frequently changing by more than +/-50 points.

Pm is cleared of such problems. I send it to Quarq and it is calibrated with the chainring on to rule out any essemly variations like bolt torque etc.

As the Quarq is solid, I would keep that over any pedal based system.

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Most suppliers have a lifetime warranty against manufacturing defects for the original owner. You’ll probably need your receipt or have your shop confirm you are the original owner.

for anyone having a similar issue and finding this topic:
Yes, a loose bb fit can cause the crank to move about and throw off the accelerometer in the power meter. Even when the movement is very slight it is enough to mess up the power readings. Quarq support confirms that it is a possibility and an engineer friend who is working on sensors in cars agrees.
So there we go. A loose BB not only creaks but also stinks :slight_smile: