Watts Lost from Bearings

I noticed the bearings on my rear wheel aren’t as smooth as they used to be - like a grinding feel to it. Nothing too serious though, and they still spin freely (i.e., spins over a minute from a light nudge).

I’ve put fresh grease on them but got me thinking if replacing bearings has a significant impact. I am able to spin it for quite a long time using my thumb, which surely isn’t much power, right? Or is it?

How many watts, if any, are lost from non-premium-but-highly-usable bearings?

I just recently went through this with my wheels and ended up installing new bearings. I found Hambini to be helpful. Check out his blog.

https://www.hambini.com/blog/post/ceramic-bearings-vs-steel-bearings…-an-engineering-opinion/

I wonder if the spin down test would take care of this? Seems like it would

This might be helpful

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I swapped from a stock GXP bottom bracket which would maybe spin 3 revolutions when spun by hand to a BB Infinite ceramic bottom bracket…you spin it by hand and it will spin for almost a minute…that has to account for at least 5 -10 watts.

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IME/O seals and torque are the drivers of what people see and feel as far as spinning a crank NOT under load. Sort of pointless but, I get it. Probably good to do to verify you didn’t mess up spacing or torque etc…

Long ago I read of 30+ BB’s (steel and ceramic/hybrid) the difference between best to worst was less than 2W. ABEC 3 or 5 Steel for me is plenty good enough.

I just listened to this the other day! Great episode and great information!
I used this information to choose a new chain lube (I’m too lazy to wax my chains)

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Just ran a couple of tests using two power readings sources, Tacx Neo 2T and Favero Assioma. Tested stock BB86 from Shimano, lightly used, vs new alloy thread together BB. At 320 watts (this is roughly my LT1) the difference is 4 watts. At 420 watts it is ~6 watts. Seems like the effect is slightly above 1% of input power. Though i suppose part of it is coming from the metal shell vs plastic cups.