Bottom bracket drag

[ericrobo]

Scott would not honour the warranty on my cracked seat stay (Scott Scale 900, carbon frame)
but I got a new frame at a discounted price, and my lbs forewent (is that a word ?) their margin...(I’m a good customer)

Under load there is a bit of a creaking rumbling noise, it’s not coming from the seat, I’ve tested that, and it doesn’t happen unless you are pedalling...

The old (not that old, done under 1400 miles on it) bottom bracket and all the other parts were built onto that new frame.

I decided to spin the cranks with the chain off, as I could feel a slight resistance going clockwise and anti-clockwise...
Just normal pressure, it only turns for a count of 3 (let’s say 2.5) seconds

Tried on my other bike (another Scale, 920)... could count upto 14 ( seconds) that B.B. has also done a similar mileage

On my fat bike it was only 3 seconds...

Anyone have any ideas ? Could it be over tightened ?

Here a video from Hawk Racing...

https://youtu.be/_UTvr1WcOT4

[In Reverse]

Hello again Eric!

It might be overtightened, or it might just be bollocksed mate. Think that's a word.

[GregMay]

that B.B. has also done a similar mileage

Think less about the miles and more about what it was ridden in, or left ridden in for extended periods of time.

FWIW, my BB that did the TDR and a few other long things (~7,000km now) still spins freely. An equivelent BB on my Spearfish has lasted less than 1,000km of wet, grubby Yorkshire weather and my less than stellar treatment of it.

[ericrobo]

"Think less about the miles and more about what it was ridden in, or left ridden in for extended periods of time."

Forgot to mention that there is no play in this BB, whereas on my other bike where the BB spins for 13 seconds, there is a bit of play...

Be interesting to see what my LBS says when i take it in tomorrow... they fitted it into the new frame...

[redefined_cycles]

Dont forget the drag factor on different bottom bracket bearings is gonna be different. For example the one you postwd a pic of, I imagine is for the sunday best bike that only sees light of day very seldom or during a race. They dont need to worry too much about being 'bombproof' and resistant to all sorts of nasties ingress. Therefore thwy are built accoedingly.

Think of a performance car/formula/F1 etc... the parts are made to work at a very high rate but only for a short period of time. Hence the sevice intervals (I think I read somethwere that they get rebuilt after a race or a few).

To cut a long story short. For example. My BBs. The one on my best/road bike is a Dura Ace or something and doesnt expect to have too much 'gunkiness' duties. I'm actually pretty surprised that its still goinig strong after the winter riding aswell as my recent Everest over 5 days attempt. When you spin it (or at least when it was new) it would spin for ages.

Now contrast the above with my brandnew XT bottom bracket. Not a pressfit but.. with this one when I first put the cranks on it would spin for maybe 4 revolutions or something. But its ok as there will be grease appropriate for the terrain and conditions (mtb stuff and that sort of thing!) As well as the seals will be appropriate to ensure they are pritecting the grease/bearings. All this extra protection adds up to extra drag.

Hope that answers part of your question... as to the creaking!!! Did you make sure you applied grease/copper paste or carbon paste around the interface where the bottom bracket was pressed into the frame??

If you youtube a guy callwd Hambini (who will shortly be doing the tech help for GCN) he had a case of a customers/youtubers bike where he found that the bottom bracket shell of the frame and the actual bottom bracket were not appropriately sized. I think the BB was spinning inside the frame or summat. He actually cured by adding mass to the frame or BB...

Sorry for the esaay. Hipe you get sorted

[Trail-rat]

"Did you make sure you applied grease/copper paste or carbon paste around the interface where the bottom bracket was pressed into the frame??"

Number 1 reason most pressfit creak I find.

I use loctite after the wife's Praxis on her mamasita kept creaking every 2 months with various grease/coperslip solutions.

Hasn't creaked for 6 months of commuting now.

Likewise when I built her pivot with the hope pressfit bb it got the self same loctite fix and has been silent

[ericrobo]

Re-defined... thanks for the info...

Would you say that a B.B. only spinning 4 times (and mine spins about 2!) as opposed to spinning 14 times, has any significant effect on your output ? (I.e. much reduced wattage)

Taking it in Monday to LBS, my mechanic there (who races National XC) reckons it’s due to the conditions it’s been run in over its 1400 miles. And it needs a new BB.

I’m not sure about this because my Scale 920, 1400 miles too, a bit of play in its BB, spins 14 times.... and it’s been ridden through winter in conditions as bad, if not worse, than the Scale 900....

[ericrobo]

Forgot to mention too about the creaking:

I cleaned the bike and put a fresh (Sram XX1) chain on... the chain I took off was XX1, and both chains fairly new .

No creaking going uphill under load !

(I swap chains after every bike clean, using the soaking in wax method)

Can’t understand why the creaking stopped

[redefined_cycles]

Thats interesting... red herring!!