Drag in BB-R9100 bottom bracket

Discuss light weight issues concerning road bikes & parts.
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savechief
Posts: 316
Joined: Wed Aug 31, 2011 2:36 am

by savechief

I've just installed a Dura Ace 9000 crankset into a BSA frame with the Shimano BB-R9100 bottom bracket. With a hard push, I get ~2 revolutions of the crank. Reading other threads, I know that this is potentially normal for Shimano bottom brackets, but not necessarily for others:

viewtopic.php?t=108002
viewtopic.php?f=3&t=144472

My takeaway from reading many threads here and on other forums is that the differences between cranks that spin 2 times and cranks that seemingly spin forever is fractions of a Watt...virtually unnoticeable in actual riding conditions, and that spinning in this unloaded condition is not indicative of its performance under load. The spin is very smooth, it just doesn't spin very long.

Help me out. Allay my fears. Or tell me that this is not good and that I should go spend $150 on a ceramic BB.
Time VXRS Ulteam (7.16 kg)
viewtopic.php?f=10&t=120268

sungod
Posts: 1565
Joined: Fri Dec 24, 2010 9:37 pm
Location: it's raining, it must be uk

by sungod

new bearings may have more drag due to excess grease, as this gets squished out the drag drops

a bearing shipped with less and/or lighter grease, or even oil, will have less drag, but it may also be more vulnerable to wear/damage as lubricant is lost and water/dirt enters

aside from that, better seals are likely to cause more drag, a bb that spins freely today may get contaminated far sooner

exactly the same applies to ceramic bearings, if a new ceramic bb is free spinning, it is not because of ceramic magic

by Weenie


AJS914
Posts: 2043
Joined: Tue Jan 28, 2014 6:52 pm

by AJS914

The fact that they can make a crank spin significantly longer has been a great snake oil sales technique for these companies. It looks good but it's meaningless. They use ceramic bearings in industrial applications when they need high rpms (not the 60-120 rpms a crank typically sees). Don't waste your money. The grease and seals on your new BB will losen up over time.

Think of it this way. Even though your crankset doesn't spin forever, you could move it along with your pinkie finger with no effort. It just doesn't require meaningful wattage to move a crankset against the drag of the new grease and bearing seals.

madik
Posts: 82
Joined: Sun Jan 08, 2017 12:44 pm

by madik

I've also installed dura ace pressfit BB recently and I felt much higher resistance of BB in comparison to my previous bike and BB.
Like sungod said I believe it's due to fresh grease in the bearing and the resistance will get close to none in few hundreds of km. Finger's crossed..

mattr
Posts: 3543
Joined: Fri May 25, 2007 6:43 pm
Location: The Grim North.

by mattr

Whats been said above, as long as the bearings are parallel and concentric, and aren't preloaded excessively. It's just drag from lubricant and seals.

You'll have that drag for the first few hours use. Then it'll spin freely for a period of time, which depends on you (how you ride, clean, look after your bike) then they'll start to wobble and need replacing.

I've got HTII bottom brackets which have been used, abused and ignored for 6-7-8 years which still work well.

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Calnago
Posts: 6226
Joined: Sun Nov 07, 2010 9:14 pm

by Calnago

I'm gonna say with only 2 revs with a good push, that something more than grease or seals is not quite right. Basically, it's either of the two things @mattr just mentioned. Since it's a BSA frame, has the shell been faced? If it has, then I'd check for excessive preload on the crank. Loosen the bolt, pull the crank back a bit, and give it another spin? Is it better? Then preload was the issue. When retightening just don't tighten as much.
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Hexsense
Posts: 462
Joined: Wed Dec 30, 2015 12:41 am

by Hexsense

Seal and grease drag doesn't scale with your pedaling force (but with your cadence which is not very big difference between 70rpm masher and 120rpm spinner anyway). So it'll stay within a couple of watt.

Foul bearing drag though, scale with the load. Good quality steel bearing maybe better than cheap ceramic bearing here they keep being in good condition with high impact force better. They stay rounder and less rigid/fragile so it doesn't chip the race and doesn't crack itself.

Ceramic bearing doesn't rust, so light oil or very thin grease can be use. Seal can also not very tight. They make crank spin forever on stand with all load come from seal and grease drag (which is already small from the beginning).
But steel bearing with proper grease and seal will stay smoother in the long run.

by Weenie


pdlpsher1
Posts: 1543
Joined: Thu Jul 19, 2012 6:09 pm
Location: CO

by pdlpsher1

From my experience the vast friction differences between BBs are mainly due to the seals and dust cap designs. Many BBs including those converter types have dust shields. So a BB could have up to four seals and two dust caps total. Seals and dust caps are there to keep dirt and water out. I have had one BB that was trashed due to water intrusion. I prefer a BB with higher friction because I don't intend to replace a BB every six months. And I believe the extra friction is very minimal in the real world.


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