SRAM Force and Rival Bottom Brackets

On Jan 25, 3:22 pm, Dan Connelly <d_j_c_o_n_n_e_l@y_a_h_o_o_._c_o_m>

Quoted message said:

CyclingNews.com reports that these bottom brackets appear to present a
high degree of resistance:http://www.cyclingnews.com/tech.php?id=tech/2006/reviews/sram_force
---
SRAM logically carries over its GXP external bottom bracket design from
its Truvativ division, but the system is in desperate need of a bearing
upgrade. The system is very intelligently designed from an engineering
standpoint (the bearings can not be inadvertently preloaded), but the
advent of high-quality hybrid ceramic bearings only serve to emphasize
the excessive levels of drag that exist in the system as it currently
stands and we can only hope that an upgrade is pending.
---
Competitive Cyclist, however, says the following:http://www.competitivecyclist.com/za/CCY?PAGE=BUY_PRODUCT_STANDARD&PR...
---
Unlike a Shimano Dura Ace or an FSA Mega Exo external BB, the GXP
bearings aren't pre-loaded. What does this mean? As we all know, Dura
Ace and Mega Exo BB's have substantial drag. Compared to a square taper
Campagnolo BB, it's like the bearings are packed in molasses. This drag
is caused by two things: The fiercely tight seals on the bearings, and
the preload on the bearings. Since GXP bearings aren't pre-loaded, all
you'll need to do is ride a few hundred miles to break in the bearing
seals, and suddenly your SRAM BB will spin with freedom that rivals a
Campy BB -- something never-before-seen in an external BB.
---

Has anyone "broken in" an SRAM bottom bracket, then checked the
rotational resistance?

It's hard for me to believe metal bearings, and not differences in seal
design, aren't responsible for a lot of the recent fuss.

thanks,
Dan

External bearings, all of them, are draggy. Even Campag ones with no
load at all(altho better than all others we have seen). Lowish end
bearings, very tight seals= drag. 'Break in the bearing seals' is nuts.
What are the seals doing? Wearing, hgetting smaller? Cart bearings mean
seal drag, no way to get arond it. A cup and ball BB, whether it be
Campag or even shimano, will always be less restricted than any cart
bearing regardless of design.

shimano's XTR, with a bearing adjust on the left side(back to the
future!!), is much better but seal drag is seal drag.

On Jan 25, 3:22 pm, Dan Connelly <d_j_c_o_n_n_e_l@y_a_h_o_o_._c_o_m>

Quoted message said:

CyclingNews.com reports that these bottom brackets appear to present a
high degree of resistance:http://www.cyclingnews.com/tech.php?id=tech/2006/reviews/sram_force
---
SRAM logically carries over its GXP external bottom bracket design from
its Truvativ division, but the system is in desperate need of a bearing
upgrade. The system is very intelligently designed from an engineering
standpoint (the bearings can not be inadvertently preloaded), but the
advent of high-quality hybrid ceramic bearings only serve to emphasize
the excessive levels of drag that exist in the system as it currently
stands and we can only hope that an upgrade is pending.
---
Competitive Cyclist, however, says the following:http://www.competitivecyclist.com/za/CCY?PAGE=BUY_PRODUCT_STANDARD&PR...
---
Unlike a Shimano Dura Ace or an FSA Mega Exo external BB, the GXP
bearings aren't pre-loaded. What does this mean? As we all know, Dura
Ace and Mega Exo BB's have substantial drag. Compared to a square taper
Campagnolo BB, it's like the bearings are packed in molasses. This drag
is caused by two things: The fiercely tight seals on the bearings, and
the preload on the bearings. Since GXP bearings aren't pre-loaded, all
you'll need to do is ride a few hundred miles to break in the bearing
seals, and suddenly your SRAM BB will spin with freedom that rivals a
Campy BB -- something never-before-seen in an external BB.
---

Has anyone "broken in" an SRAM bottom bracket, then checked the
rotational resistance?

It's hard for me to believe metal bearings, and not differences in seal
design, aren't responsible for a lot of the recent fuss.

thanks,
Dan

AND I will add that by adding bearings that cost a factor of
10(ceramic) does not overrule seal drag. Ceramic bearing balls are one
of the biggest hypes I have seen in bicycles.

Quoted message said:

AND I will add that by adding bearings that cost a factor of
10(ceramic) does not overrule seal drag. Ceramic bearing balls are one
of the biggest hypes I have seen in bicycles.

However, VeloNews DID observe a substantial improvement with the FSA
ceramic bottom brackets. Is this because the seal design is improved
with the more expensive bearings?

The difference in watts as they tested was small, but if you assume drag
force is proportional to load force, for reasonable bearing loads, the
difference in power was significant.

Consider: the difference between the Cervelo Soloist and Soloist SL is
$1300 and 200 grams: $6.50/gram. Weight contributes roughly 10% to
speed on the flats, roughly 90% on the hills. Therefore the savings in
power, assuming 10kg of stuff and 70kg of rider, is from 1/4000 to 1/440
from flat to climbing (obviously it doesn't help descending!).

On the other hand, a 1% improvement in power transfer efficiency saves
1/100 of power.

So if folks are shelling $1300 for a 1/4000 to 1/440 advantage (let's
make it an even 1/1000), then you'd think they's be willing to pay $13k
for a 1% power advantage. $300 for a bottom bracket is cheap in
comparison 🙂.

Dan

P.S. Of course, drivetrain efficiency doesn't have the same Peet's
Coffee bragging rights... Being able to say, for example, "13.6" really
brings attention, admiration, and respect.

On Jan 26, 9:38 am, Dan Connelly <d_j_c_o_n_n_e_l@y_a_h_o_o_._c_o_m>

Quoted message said:

Quoted message said:

AND I will add that by adding bearings that cost a factor of
10(ceramic) does not overrule seal drag. Ceramic bearing balls are one
of the biggest hypes I have seen in bicycles.However, VeloNews DID observe a substantial improvement with the FSA

ceramic bottom brackets. Is this because the seal design is improved
with the more expensive bearings?

The difference in watts as they tested was small, but if you assume drag
force is proportional to load force, for reasonable bearing loads, the
difference in power was significant.

Not significant, measurable but your definition of substantial is
different than mine. Substantial to me means a huge, demonstratable,
repeatable difference.

Quoted message said:

Consider: the difference between the Cervelo Soloist and Soloist SL is
$1300 and 200 grams: $6.50/gram. Weight contributes roughly 10% to
speed on the flats, roughly 90% on the hills. Therefore the savings in
power, assuming 10kg of stuff and 70kg of rider, is from 1/4000 to 1/440
from flat to climbing (obviously it doesn't help descending!).

On the other hand, a 1% improvement in power transfer efficiency saves
1/100 of power.

So if folks are shelling $1300 for a 1/4000 to 1/440 advantage (let's
make it an even 1/1000), then you'd think they's be willing to pay $13k
for a 1% power advantage. $300 for a bottom bracket is cheap in
comparison 🙂.

Dan

P.S. Of course, drivetrain efficiency doesn't have the same Peet's
Coffee bragging rights... Being able to say, for example, "13.6" really
brings attention, admiration, and respect.

I'll assume your numbers are correxct so about 4-5 watts?? $300 for a
BB that 'may' alloow you to generate a single digit watt
increase..worth it to whom?

And remember these numbers assume all else is equal, one rider or
numerous riders vary hugely day to day, rider to rider. Altho there is
not much you can qualtify on a bicycle, those things that you can take
overly huge importance.

On Jan 26, 10:38 am, Dan Connelly <d_j_c_o_n_n_e_l@y_a_h_o_o_._c_o_m>

Quoted message said:

On the other hand, a 1% improvement in power transfer efficiency saves
1/100 of power.

Yes... but where did you get that number?

Dan Connelly said:

CyclingNews.com reports that these bottom brackets appear to present a
high degree of resistance:
http://www.cyclingnews.com/tech.php?id=tech/2006/reviews/sram_force
---
SRAM logically carries over its GXP external bottom bracket design from
its Truvativ division, but the system is in desperate need of a bearing
upgrade. The system is very intelligently designed from an engineering
standpoint (the bearings can not be inadvertently preloaded), but the
advent of high-quality hybrid ceramic bearings only serve to emphasize
the excessive levels of drag that exist in the system as it currently
stands and we can only hope that an upgrade is pending.
---
Competitive Cyclist, however, says the following:
http://www.competitivecyclist.com/za/CCY?PAGE=BUY_PRODUCT_STANDARD&PRODUCT.ID=3387&CATEGORY.ID=6&MODE=&TFC=TRUE

---
Unlike a Shimano Dura Ace or an FSA Mega Exo external BB, the GXP
bearings aren't pre-loaded. What does this mean? As we all know, Dura
Ace and Mega Exo BB's have substantial drag. Compared to a square taper
Campagnolo BB, it's like the bearings are packed in molasses. This drag
is caused by two things: The fiercely tight seals on the bearings, and
the preload on the bearings. Since GXP bearings aren't pre-loaded, all
you'll need to do is ride a few hundred miles to break in the bearing
seals, and suddenly your SRAM BB will spin with freedom that rivals a
Campy BB -- something never-before-seen in an external BB.
---

Has anyone "broken in" an SRAM bottom bracket, then checked the
rotational resistance?

It's hard for me to believe metal bearings, and not differences in seal
design, aren't responsible for a lot of the recent fuss.

Do you really believe ceramic balls have any performance advantage
beyond a couple grams savings? Line up and pay your money if you do.

I don't. If you've saved every other cheaper weight they make some sense
but don't kid yourself about 'efficiency'.

Oh, and ceramic balls can run in temperatures beyond the pilot's death
of course! That's gotta be a real advantage right? What's _that_ worth?
--
Andrew Muzi
www.yellowjersey.org
Open every day since 1 April, 1971

I have some experience with the Truvativ version of the crank with
external bearings. My friend had her left crank arm fall off at about
5000 miles. The cranks had never seen a wrench since she purchased
the bike. The left side bearings were shot. She bought a new set of
bearings ($50) and I put the crank back on. The amount of drag seemed
high to me when the crank was tightened to the specified torque.
After some fretting and secretly spinning new cranks on bikes in
shops, I decided that the drag was normal. Last week, after about 500
miles, the left crank feel off again.

It seems to me that the design is flawed: Attaching the crank to the
axle should be a seperate step than loading the bearings. I am
unaware of any other crank that does this, although this Truvativ
external bearing design is the only external bearing crank I have ever
worked on.

Now she has taken advantage of 10 speed hype to buy a 9 speed shimano
crank and reserve of bottom brackets. Hopefully this will last for a
while.

Now the only question is: what to do with the old crank? jf

southphilly said:

I have some experience with the Truvativ version of the crank with
external bearings. My friend had her left crank arm fall off at about
5000 miles. The cranks had never seen a wrench since she purchased
the bike. The left side bearings were shot. She bought a new set of
bearings ($50) and I put the crank back on. The amount of drag seemed
high to me when the crank was tightened to the specified torque.
After some fretting and secretly spinning new cranks on bikes in
shops, I decided that the drag was normal. Last week, after about 500
miles, the left crank feel off again.

It seems to me that the design is flawed: Attaching the crank to the
axle should be a seperate step than loading the bearings. I am
unaware of any other crank that does this, although this Truvativ
external bearing design is the only external bearing crank I have ever
worked on.

Now she has taken advantage of 10 speed hype to buy a 9 speed shimano
crank and reserve of bottom brackets. Hopefully this will last for a
while.

Now the only question is: what to do with the old crank?

Wall art? Wind chime? Landfill?

southphilly said:

I have some experience with the Truvativ version of the crank with
external bearings. My friend had her left crank arm fall off at about
5000 miles. The cranks had never seen a wrench since she purchased
the bike. The left side bearings were shot. She bought a new set of
bearings ($50) and I put the crank back on. The amount of drag seemed
high to me when the crank was tightened to the specified torque.
After some fretting and secretly spinning new cranks on bikes in
shops, I decided that the drag was normal. Last week, after about 500
miles, the left crank feel off again.

It seems to me that the design is flawed: Attaching the crank to the
axle should be a seperate step than loading the bearings. I am
unaware of any other crank that does this, although this Truvativ
external bearing design is the only external bearing crank I have ever
worked on.

Now she has taken advantage of 10 speed hype to buy a 9 speed shimano
crank and reserve of bottom brackets. Hopefully this will last for a
while.

Now the only question is: what to do with the old crank? jf

I made a pretty cool wind chime out of crank arm, chainrings,
cogs...too bad Truvativ is hooked to Sram...haven't seen much good
about Truvativ...