# Is my old bottom bracket slowing me down



## Trek_5200 (Apr 21, 2013)

Can anyone opine on the relative efficiencies of a 6500 vs a 6800 bottom bracket design. It seems even amongst threaded designs there's been a good deal of evolution over the past decade. How inefficient is the older 6500.


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## Peter P. (Dec 30, 2006)

No. Chain and bearing losses due to friction absorb such a small amount of energy (3-5% of power input) as to be meaningless. Since you're concerned with just one bearing (the BB) then losses are much smaller, even if you include the cartridge bearing seals.

As long as the bottom bracket bearings aren't grinding or have slop, there's no reason to replace them.


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## ibericb (Oct 28, 2014)

Overall drivetrain efficiency is on the order of 97-98%, provided everything is working as it should. You're looking at very, very small differences at most, like a fraction of a percent, in efficiency provided that the older one isn't suffering from wear/tear issues or poor maintenance.

edit added - this article may give you some perspective on drivetrain efficiencies.


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## DaveG (Feb 4, 2004)

Trek_5200 said:


> Can anyone opine on the relative efficiencies of a 6500 vs a 6800 bottom bracket design. It seems even amongst threaded designs there's been a good deal of evolution over the past decade. How inefficient is the older 6500.


I cant think of any advances in BB design that have reduced friction. If anything, old school loose bearing BB's have less friction than today's sealed cartridge bearings. If you really want to blow some cash there is always pricey ceramic bearing BBs.


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## ibericb (Oct 28, 2014)

I remembered that Friction Facts (the guys who did the famous chain lube power loss studies) had tested various bottom brackets for their friction losses. Unfortunately, you can only get the results with a $7.95 purchase. I just searched to see if someone had (improperly) posted the report, and found this summary article at BikeRadar instead. While the article isn't definitive, it gives you a range of best to worst, and points to a couple of worthwhile differences (sealing and grease). If you look closely at the big bar graph at the bottom of the Lesson #2 section, you will see ceramic and steel dominating opposite ends, but the across the majority of the graph you'll see the two randomly distributed. The point is (see Lesson #1), ceramic isn't always better.


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## goodboyr (Apr 19, 2006)

I've got it. Suffice to say we are talking less than 1 watt difference between bb's.


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## DaveG (Feb 4, 2004)

ibericb said:


> I remembered that Friction Facts (the guys who did the famous chain lube power loss studies) had tested various bottom brackets for their friction losses. Unfortunately, you can only get the results with a $7.95 purchase. I just searched to see if someone had (improperly) posted the report, and found this summary article at BikeRadar instead. While the article isn't definitive, it gives you a range of best to worst, and points to a couple of worthwhile differences (sealing and grease). If you look closely at the big bar graph at the bottom of the Lesson #2 section, you will see ceramic and steel dominating opposite ends, but the across the majority of the graph you'll see the two randomly distributed. The point is (see Lesson #1), ceramic isn't always better.


Interesting article. It kinda blows my excuse that my BB was holding me back; turns out I'm just slow.


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## Jay Strongbow (May 8, 2010)

DaveG said:


> Interesting article. It kinda blows my excuse that my BB was holding me back; turns out I'm just slow.


Does your stem have titanium bolts? Aero helmet? You're not still using alloy rims are you? It might not be the BB but there's plenty more to blame it on.


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## ibericb (Oct 28, 2014)

Okay you've got several opinions. If, however, you're determined to upgrade your BB in the hopes of better performance, might as well go for gold. It's the one that Fabian Cancellera was at one time accused of using illegally (it wasn't then commercially available) to get an advantage.


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## DaveG (Feb 4, 2004)

ibericb said:


> Okay you've got several opinions. If, however, you're determined to upgrade your BB in the hopes of better performance, might as well go for gold. It's the one that Fabian Cancellera was at one time accused of using illegally (it wasn't then commercially available) to get an advantage.


Don't waste your money saving a couple of watts. If you want to buy speed, go big. This will give you an extra 200 watts whenever you need it. Also approved /endorsed by Fabian Cancellara

vivax assist 4.0 - vom Bike zum leichten E-Bike


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## Trek_5200 (Apr 21, 2013)

DaveG said:


> Don't waste your money saving a couple of watts. If you want to buy speed, go big. This will give you an extra 200 watts whenever you need it. Also approved /endorsed by Fabian Cancellara
> 
> vivax assist 4.0 - vom Bike zum leichten E-Bike


 No plans to to upgrade the BB given the opinions here. I've decided to chalk up the significant speed difference in the two bikes to a lot of little things adding up.


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## ibericb (Oct 28, 2014)

Trek_5200 said:


> No plans to to upgrade the BB given the opinions here. I've decided to chalk up the significant speed difference in the two bikes to a lot of little things adding up.


How significant, and under what riding conditions (flats, hills,?)? How different are the bikes?

Here's a blog entry by Coach Alex Simmons. Scroll down to the first graphic (click on it to get the big version), and take a close look at the various components that make up total resistance under various conditions (road grade). We tend to dismiss the drivetrain as a power sink because it tends to be a very small contributors to total resistance on a bike with everything well tuned and working as it should. Stating the obvious, get something out of whack and you may be taking a hit on power. Several of us dismissed your BB question because it would typically be negligible, assuming it's still in good condition, and the change from a good 6500 to a 6800 should be negligible overall.

In comparing your performance across bikes I would suggest you look at how gearing, gear selection, wear, tuning, etc. can affect drivetrain efficiency. I'm guessing your slow bike is geared and equipped differently, or at least operating differently. One well detailed study (see article titled "On the efficiency of bicycle chain drives", page 3) found that drive train efficiency varied significantly (98.6% to 80.9%) with chain tension, which could be appreciably altered by gearing combinations, or other drive train differences resulting in markedly different efficiencies.

You may be on the right track, but just looking at the wrong part of the system unless your BB is somehow trashed.


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## Trek_5200 (Apr 21, 2013)

ibericb said:


> How significant, and under what riding conditions (flats, hills,?)? How different are the bikes?
> 
> Here's a blog entry by Coach Alex Simmons. Scroll down to the first graphic (click on it to get the big version), and take a close look at the various components that make up total resistance under various conditions (road grade). We tend to dismiss the drivetrain as a power sink because it tends to be a very small contributors to total resistance on a bike with everything well tuned and working as it should. Stating the obvious, get something out of whack and you may be taking a hit on power. Several of us dismissed your BB question because it would typically be negligible, assuming it's still in good condition, and the change from a good 6500 to a 6800 should be negligible overall.
> 
> ...


 Both bikes are 53-39 gearing but the Trek is 12-25 with 9 gears total while the Colnago is 11-28 with 11 gears total. I just don't think its gears.


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## MR_GRUMPY (Aug 21, 2002)

If you already have a 9 speed 6500 setup, you could probably save 3-4 watts if you switch to a BB7700 and wash the grease out and replace with oil. You would only have to take it all apart to re-oil not more than once a week.
.


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## velodog (Sep 26, 2007)

MR_GRUMPY said:


> If you already have a 9 speed 6500 setup, you could probably save 3-4 watts if you switch to a BB7700 and wash the grease out and replace with oil. You would only have to take it all apart to re-oil not more than once a week.
> .


A BB with an oil port would save all the disassembly time.


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## ibericb (Oct 28, 2014)

velodog said:


> A BB with an oil port would save all the disassembly time.
> 
> View attachment 302768



I very vaguely recall having a bike 50+ years ago that had a flip-cap oil cup on the read hub. Never seen one of a BB. Funny, don't recall drain plug.




MR_GRUMPY said:


> If you already have a 9 speed 6500 setup, you could probably save 3-4 watts if you switch to a BB7700 and wash the grease out and replace with oil. You would only have to take it all apart to re-oil not more than once a week.
> .


On a BB, realistically, 1 watt, 2 max if you eliminate all friction, unless the existing bearings or race are crap. For an 85 kg rider, 9kg bike, flats, no wind, etc., the difference that 2 watts makes at an effort of 198 vs. 200 watts is ~ 0.6 sec's/km. At higher power levels it becomes less, heading to zero. Lennard Zinn was right.


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## Kerry Irons (Feb 25, 2002)

ibericb said:


> I very vaguely recall having a bike 50+ years ago that had a flip-cap oil cup on the read hub.


Might well have been a 3-speed internally geared hub, like a Sturmey-Archer.


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## ibericb (Oct 28, 2014)

MR_GRUMPY said:


> If you already have a 9 speed 6500 setup, you could probably save 3-4 watts if you switch to a BB7700 and wash the grease out and replace with oil. You would only have to take it all apart to re-oil not more than once a week.
> .





Kerry Irons said:


> Might well have been a 3-speed internally geared hub, like a Sturmey-Archer.


Might've been -- my recollection of that bike is pretty vague.


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## MR_GRUMPY (Aug 21, 2002)

"On a BB, realistically, 1 watt, 2 max if you eliminate all friction, unless the existing bearings or race are crap. For an 85 kg rider, 9kg bike, flats, no wind, etc., the difference that 2 watts makes at an effort of 198 vs. 200 watts is ~ 0.6 sec's/km."

For a 40K TT, that 0.6 sec/km would give you a 24 second advantage.
.


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## ibericb (Oct 28, 2014)

MR_GRUMPY said:


> "On a BB, realistically, 1 watt, 2 max if you eliminate all friction, unless the existing bearings or race are crap. For an 85 kg rider, 9kg bike, flats, no wind, etc., the difference that 2 watts makes at an effort of 198 vs. 200 watts is ~ 0.6 sec's/km."
> 
> For a 40K TT, that 0.6 sec/km would give you a 24 second advantage.
> .


Yep, if you could get 2 watts out. Nobody riding at that level is going to change that much from a reasonable BB. Further, at higher power output the difference shrinks as it is a smaller percentage. How about this -- difference of 1 watt, 300 vs 299, which would be huge, over 40 km, everything else the same. The difference over 40 km is 4.8 sec's. That's could well be a win, and worth worrying about if you're competing.


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