Yellow Saddle
Guru
- Location
- Loch side.
Yup, there's hope.
Noisy BB
- Thread starter ozboz
- Start date
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Yup, there's hope.
Jody
Stubborn git
It is. The reason I ask though is I replaced mine last year when doing the frame bearings and some other jobs. Nothing wrong with it when replaced but the new one has took a lot of hammer and its still not giving me any grief.
Yellow Saddle
Guru
- Location
- Loch side.
No. By definition the more expensive ones since all carbon frames nowadays have this abomination. Some aluminium frames too. Price is not the issue, it is a fundamental design flaw.
Yellow Saddle
Guru
- Location
- Loch side.
Give it time....
Jody
Stubborn git
Be positive. You never know
confusedcyclist
Veteran
Nope! Only press fit. They are physically pressed into the frame, your's are threaded and the bearings are external.
Yellow Saddle
Guru
- Location
- Loch side.
I found this piece of bumph relating to SRAM's Pressfit BB30 on the company's website.
"This is a new design led by SRAM. It’s all the best from BB30 and Press-Fit bottom brackets in one captivating package.
This bottom bracket is designed for cut cut cut cut.
Advantages: Huge weight savings, narrow Q-factor, more ankle clearance, greater bearing durability, stiffer/stronger crank construction, simple installation.
Allows for larger diameter frame tubes increasing frame stiffness.
Drawbacks: Still searching."
"This is a new design led by SRAM. It’s all the best from BB30 and Press-Fit bottom brackets in one captivating package.
This bottom bracket is designed for cut cut cut cut.
Advantages: Huge weight savings, narrow Q-factor, more ankle clearance, greater bearing durability, stiffer/stronger crank construction, simple installation.
Allows for larger diameter frame tubes increasing frame stiffness.
Drawbacks: Still searching."
Globalti
Legendary Member
It may not be the bearings fretting in their shells. i've posted this alternative explanation a few times but here it is again:
https://www.cyclechat.net/threads/cannondale-bb30-bottom-bracket.196684/post-4207483
https://www.cyclechat.net/threads/cannondale-bb30-bottom-bracket.196684/post-4207483
I replaced a BB30 on a Cannondale Synapse around 3 months ago using this method (after reading it here) and it's been quiet ever since. Fingers crossed.
Having just removed and cleaned the seatpost too, the bike runs almost silently.
Sheffield_Tiger
Guru
Never had all this with mild steel notched b/b axles and cotter pins
Okay, the cotter pin would come loose, the axle would wear away and you'd be left with a left crank flopping about 10 degrees per rotation
But it wouldn't be noisy. And if it was, you just opened the cap in the frame and filled it with 3-in-1
Progress? Pah!
Okay, the cotter pin would come loose, the axle would wear away and you'd be left with a left crank flopping about 10 degrees per rotation
But it wouldn't be noisy. And if it was, you just opened the cap in the frame and filled it with 3-in-1
Progress? Pah!
Why is GXP so bad? Just curious.
Yellow Saddle
Guru
- Location
- Loch side.
It's a fair question and I should back up my claim. It's a bit complicated, but I'll try my best.
Firstly, GXP is proprietary. That's bad for all of us. It rules out competition and of course price fluiditty. Hollowtech (Shimano) is now a licensed standard and you can buy plenty of cheap BBs for Shimano cranks. But being proprietary alone is not the worst feature of GXP. It is also dodgy engineering fuelled by pride and stubbornness .
First thing to understand is the problem with all of these hollow-crank-with-outboard-bearing technologies. They were created to reduce the weight of the square taper BB. Which they do. Full marks there.
However, by using a thin hollow tube as the crank axle (shaft) you can only get stiffness if you increase the shaft's diameter. Think Cannondale downtube. The shaft had to be so big that it and bearings would no longer fit inside a standard BB shell - hence the outboard bearing solution. That's fine, and a kinda elegant solution too. Shimano's invention had both ends of the shaft rotate inside bearings of 24mm ID. (It is not exactly 24mm ID but a bit bigger 'cause there's a plastic sleeve inbetween bearing and shaft). It was extremely successful (financially but not durable) and popular. It's main weakness wasn't identified for a long time. More about that later. Shimano patented the design.
SRAM, being a stubborn proud American company didn't want to pay for the patent (perhaps Shimano wouldn't sell to them) and re-engineered the concept. They kept the 24mm shaft but to make it different, stepped the left hand side down to 21mm. That got them past the patent. However, the stiffness of a shaft is hugely dependent on diameter. "Stiffness" requires some explanation.
What is not obvious is that pedalling forces from the right leg don't go through the shaft. Your foot presses on the crank and the crank is connected to the spider and that to the chain. No force goes through the shaft when your right leg pushes down. When your left leg pushes down, the force goes into the left crank, through the shaft, into the spider etc etc. The stiffness (resistance to twist and resistance to bend) of that shaft is determined by the shaft's diameter. By making it smaller on the load-bearing left hand side, they committed a stupidly.
So what if it bends and twists a bit, I hear you say? Well, you don't care but the bearing cares. Firstly, it pulls the bearing's inner race out of alignment with the outer race. If you imagine the balls running between two tracks which are perfectly aligned, and you twist the tracks so they are not running at angles to each other, you can imagine what that does to the bearing balls - they fail prematurely. They fail at a ratio 3 to 1, left to right. Compared to similar bearings used in industry, they fail in a much shorter service life.
By weaking the shaft on the already-compromised left hand side, GXP left side bearings fails even quicker than 24mm Hollowtech bearings.
But that's not all.
Twisting forces have an effect on the bearing/shaft interface too. Shimano anticipated that and inserted a plastic sleeve between the two. That way any twisting and bending is taken up by plastic deformation in the plastic sleeve. It also eliminates noises. SRAM's left hand side is metal on metal.
Again, the movement between bearing and shaft may seem trivial, but just listen to BB30 owners and you'll hear howls of disappointment.
Look at this thread here: https://www.cyclechat.net/threads/cannondale-bb30-bottom-bracket.196684/post-4207483
@Globalti posted a nice picture there of his BB30 crank suffering from bearing fretting. Compare right to left and note the difference. Cannondale, the lead inventor of BB30 thought that they could get away with an aluminium shaft if they increased diameter to 30mm. Wrong!
Again, the forces between the bearing and shaft are not obvious. They're simultaneous bend and twist forces. The twist forces cause shaft/bearing contact points to shift not radially, but axially. To understand this, have a look at the pool noodle scene in this video on Youtube. It is the best explanation I've seen for what happens when a shaft twists.
View: https://www.youtube.com/watch?v=yJXKoBTN0-U&t=314s
You only have to watch up to the 2 minute mark. If you care for a bit of maths, you'll also discover what effect diameter has on stiffness.
By using a 21mm shaft end SRAM created a monster. Proprietary, weak and expensive. To be avoided. BB30 is equally bad.
Yellow Saddle
Guru
- Location
- Loch side.
Never had all this with mild steel notched b/b axles and cotter pins
Okay, the cotter pin would come loose, the axle would wear away and you'd be left with a left crank flopping about 10 degrees per rotation
But it wouldn't be noisy. And if it was, you just opened the cap in the frame and filled it with 3-in-1
Progress? Pah!
I don't think those axles were made from mild steel.
