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PostPosted: Mon Oct 08, 2012 3:48 am 
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Hi,
So after a ride through the mud last weekend, I decided I'd do a full teardown of my Scott Addict to thoroughly clean and overhaul everything. Once I took the chain and pedals off the bike, I spun the cranks by hand and found that it only seemed to spin maybe twice before stopping. Since I've had the bike for maybe 2 years, I thought maybe it was possible the bearings were shot. It uses a press-fit BB86 version of BB-7900 bottom bracket. I then started working on a time trial project bike of mine and installed a brand new external bearing BB-7900 bottom bracket. After installing the cranks, I spun the cranks by hand and found the same level of drag as my Addict.
Is this amount of drag somehow normal on newer bottom brackets? I have some older bikes using el cheapo square taper cartridge bearing bottom brackets that I can spin the crank for 10-15 revolutions with one push. It seems odd that the drag is so much higher on these Dura Ace BB's. Am I doing something wrong? I tried loosening the pre-load dust cap, but even with just the drive side crank arm on seems to be dragging.


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Posted: Mon Oct 08, 2012 3:48 am 


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PostPosted: Mon Oct 08, 2012 4:24 am 
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Go find an old steel bike with a loose ball bearing bottom bracket that has been sitting outside for years.
It will spin 50 times with one push. The amount of drag you feel sounds normal.
If while you are pushing it, you hear rumbling or feel grittiness, then it is time to replace it.

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PostPosted: Mon Oct 08, 2012 8:08 am 
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It is ok, the BBs have been designed for a long lifetime. It will get better after a few thousand km/miles, but not much.
A BB with less seals would mean they would wear out quicker and that would generate a lot of unsatisfied bike owners and warranty replacements.

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PostPosted: Mon Oct 08, 2012 12:28 pm 
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Location: Sydney
2 revolutions does sound a bit tight tho. my FSA BB (external bearing cups) spins very freely and its just gone 3 yrs old. FWIW, i also removed a UN73 shimano square taper bb last weekend and it spun very freely before i took it out- easily the 10-15 revs you suggest. I know its a different spindle and older bb but still...


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PostPosted: Mon Oct 08, 2012 2:24 pm 
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Location: Natovi Landing
howler wrote:
2 revolutions does sound a bit tight tho. my FSA BB (external bearing cups) spins very freely and its just gone 3 yrs old. FWIW, i also removed a UN73 shimano square taper bb last weekend and it spun very freely before i took it out- easily the 10-15 revs you suggest. I know its a different spindle and older bb but still...


2 revs with DA sounds normal.

square taper don't have the same pre-loading which generates drag. getting the torque right, removing seals, going ceramic, and very easy on the grease will all help, but won't make it square taper.


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PostPosted: Mon Oct 08, 2012 5:06 pm 
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What was the pointing all this BB "innovations" of the last 2 decades if it has 10x more drag than shit from the 70's? Just stiffness? Better seals and durability? Maybe I should just switch to Phil wood.


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PostPosted: Mon Oct 08, 2012 5:57 pm 
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The drag is not significant, your tyres rolling resistance is orders of magnitude more.

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PostPosted: Mon Oct 08, 2012 8:39 pm 
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Omiar wrote:
The drag is not significant, your tyres rolling resistance is orders of magnitude more.

I believe you, but if this is true, why would anybody buy ceramic BB bearings?


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PostPosted: Mon Oct 08, 2012 9:37 pm 
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^^
That's an extremely good question.


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PostPosted: Mon Oct 08, 2012 9:48 pm 
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kulivontot wrote:
I believe you, but if this is true, why would anybody buy ceramic BB bearings?

Marketing.

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Last edited by fa63 on Mon Oct 08, 2012 10:18 pm, edited 1 time in total.

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PostPosted: Mon Oct 08, 2012 9:52 pm 
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"Free spin" is basically meaningless. How the bearings perform under load is far more important. An outboard BB bearing that was optimized for free spin in the stand, wouldn't survive very long out in the real world.

My Dura-Ace BBs spin the same number of revolutions, and I don't worry about it.

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PostPosted: Mon Oct 08, 2012 9:58 pm 
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Each and every pro that uses DA uses ceramics everywhere-just ask Bradders - and I have definately found a sig improvement using SR ceramics in the jockey wheels. They reduce friction, period. Shimano, being a multi billion dollar company, can't be bothered, thinking no one will notice.


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PostPosted: Tue Oct 09, 2012 2:00 am 
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each and every pro that uses ceramics use them for the psychological benefit - period.
when the best of the best ceramic bearings in wheels save a maximum of 3seconds over 40k, it's predominantly in your head. derailleur pulleys? please. theyre loaded with only pulley cage tension.
the whole notion of using ceramic bearings in bicycles started off as a silly "show special", or something along those lines. it was never meant to be taken seriously.
but like anything, if a pro knows that the guy next to you has any sort of "advantage", it'll just gnaw at you.


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PostPosted: Tue Oct 09, 2012 2:49 am 
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As pointed out, how well the bearings spin without load on the stand is moot ... pointless. What matters is how well the bearings spin under load.

Bearings under load will deform. Be it the race or the balls.

A well designed and applied bearing will be preloaded such that it deforms to its optimum dimensions under its designed load.
The reverse is true too.

Same thing applies for wheels and BB bearings. If you want to check how well they roll, you need to load them.

For wheels, if you spin the wheels on the stand and compared to if you straddle the bike and roll it down a long gentle hill with them, their performances will most likely NOT be the same.

For BB bearings, if you can, mount about 70kg worth of weights equally between the 2 sides (35kg / 35kg) on weight discs and spin them from there. How well they spin would then be the 'real world' result.


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Posted: Tue Oct 09, 2012 2:49 am 


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PostPosted: Tue Oct 09, 2012 7:07 am 
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Certainly I haven't gone the full ceramic route, Campy's steel bearings being of such high quality as it is. But it's not in my head that the jockey's have made a real difference, in real world conditions, esp under stress going up inclines.I'm not going to CULT me BB anytime soon, however, and there we are in accord.

We can certainly argue that top ceramics/steel bearings in the wheels make a difference, and I'm kicking myself a little that I didn't fit either record hubs or Zonda's instead of sludgy Elites. One ceramic front wheel spun for 12 mins with a 3 mph push, and yes, the owner did see a real world difference.


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