The Campag BB86 cups are the lightest option as well. Not having a bonded threaded insert in the BB seemed like a good idea to me.
The only downside is the potential for the cups to creak but loctite can cure that.
PF30 gives the most flexibility of using different BB standards with adaptors. Its also easier to make than BB30 as the cups don't need the same tolerances, and hence will last more changes.
You can then use an adaptor to run campy, then if/when campy comes out with a BB30 cranks you can easily change. If you then want a 386 crank there will be adaptors for that. And all these changes will not damage the threads or press fit of the frame.
BB86 is not PF30. Different widths, and most importantly different OD/ID bearings.
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laager wrote:I guess the question is really press fit (all types) v BSA.
You know I have not heard of anyone having problems with BB adapters, but the word 'adapter' is enough to put some off.
The other good 'standard' would be the EVO386. But that has backward compatibility issues with older cup-and cone as well as cartridge BB's designed for ITA or BSA treads.
1. Is the frame BB section too soft? Or is the spindle too soft? Former, you go w BB86, latter, you go with BB30/PF30.
2. As my rough drawing shows,
Pros and Cons of 86 are:
less ankle clearance,
narrow but thick walled crank arms
offset spider to maintain chainline
compatibility one way street.
So the conclusion is against BB86.
From a pure design perspective (and longer term view), outboard bearings have pushed crankarms too far out with very little room left for them. It now gives the BB shell plenty of room to be optimized but the overal system is pretty f*cked up.
Crank arms actually take MORE load than the BB shell but they have no room to go large and hollow and can only use thick walls to compensate (just put a Campy SR crank arm next to a R5/Evo downtube and compare). Pls look at the tyical cross section of a modern crank arm, a modern downtube and a modern BB shell (as well as thickness) in my little graph. Ideally you'd want to share the limited space between two feet among the various parts to achieve the best overall weight and stiffness. But manufacturering is fragmented hence hard to have a coordinated effort. Look's system is really an improvement but they are too damn proprietary (plus the triangle insert thing is absurd). This is why I thought I'd love BB386 but decided against it.
From a practical perspective, looks like the highest regarded cranks today would fit PF30/BB30.
Laager- I think that is a poor execution of what can be done with BB86 or 386. However because the chain rings must be set inboard and around the DS of the frame cups you can't grow the DT/ST or CS outwards that way like you could on the NDS. Have a look at frames more like TREK or maybe even the new giants and you will see they are assymetric to use the extra width on the NDS.
Re the Fondie, looks like it simply extended the sleeve "just to be compatible" and did not take adavntage of the logic behind the design.
To answer Laager's question, this might still be better than BSA though. It's just that the wider platform is somewhat wasted because the downtube and chainstays didn't go wider. It's definitely not worse than BSA.
elviento wrote:Phill, you are right, and the downtube actually also holds the entire frame together. I am not saying the crank arm should be 50x60mm, but 45x30mm would go quite a long way to begin with.
In a down tube you have basically 2 forces: bending and torsion. However in a crankarm the bending forces are a lot bigger than the torsion. It makes no sense to make the crankarms a lot 'thicker' it better to make the 'wider'.
I would choose the PF30.