Threaded vs Press Fit vs Sleeved Bottom Brackets
More on this later - a quick summary of the three styles of Hollowtech type bottom brackets (non taper).
Theory of operation
A bottom bracket has to cope with a rotation up to about 120 rpm / rotations per minute. The biggest forces come from the weight of the cyclist and the push forces due to pedalling. This causes a rocking/torque force on the bearings as well as an up/down force.
In a threaded bottom bracket the bracket is held in place by a screw thread, like a very large diameter bolt. See the jagged red line in the diagram above between the bike frame and bearing cup.
This is a very solid design. Proper installation is necessary to ensure the bearing cup remains tightly screwed into the bike frame.
For carbon frames the thread isn't cut into the frame; separate threaded tube bonded into the frame when it's made. This ensures a good degree of alignment.
Press fit bottom bracket
Here's the press fit version. Rather than having a nice solid thread to hold the bearing cup, the design relies on friction between the bike frame and bearing cup to resist movement. The dashed red line is a friction surface.
This works well when the bike frame has the correct size hole for the bearing cup and sufficient pressure is created by the bearing cup having a proper interference fit with the frame. As noted else in LaVita Tech Shed, this design creaks when contaminant gets between the bike frame and bearing cup.
Once you hear creaking the bearing cup has already been damaged and should be replaced immediately to avoid further damage to the frame. We recommend adding low strength Loctite when reassembling a bottom bracket that has started creaking as the frame surface will have damage.
Hybrid / Sleeved / 'Hambini' bottom brackets
In a sleeved press fit bottom bracket (as used with Hambini replacement brackets), the Press Fit bottom bracket includes a structural element between two sides of the frame. The rocking force is distributed across the width of the bottom bracket. There is still a friction surface between the frame and (long) bearing cup but the cup is likely to be smaller diameter and have a much lower level of friction.
There are many advantages to this design. It can be installed into a standard BB86 / BB90 / BB92 press fit frame and as long as it's held in place by moderate friction or a threaded element in the non-crank side it's almost impossible for the bearing cup to creak against the frame.
Some frame manufacturers have faced criticism for delivering frames where the two sides of the bottom bracket are not axially aligned - both angular and offset misalignment. With press fit bottom brackets these frames will quickly creak because the bearing cup friction surface will be subject to high harmonic forces; this will likely overwhelm and damage the interference fit before the bearing is damaged although the bearing could fail first.
A sleeved press fit bracket as per this design will correct frame defects because it has its own shape and doesn't rely on the frame.
A note about LaVita frames
LaVita frames use BB86 press fit bottom brackets. We randomly sample LaVita frames and the bottom bracket holes diameter consistently achieve 41mm +- 0.05mm at all angular measurements for a consistent friction surface pressure with the bearing cup. The frames are moulded onto a straight machined tube that passes through the frame so there is an extremely high level of axial alignment between left and right holes.
An engineering metal rule sits flat on the bottom bracket of a LaVita frame. You can see the bare carbon weave and the ruler showing a high degree of parallelism along the hole and in alignment with the other side of the frame
Our bottom brackets
We will shortly stock Press Fit bottom brackets to a similar design to Shimano, and a hybrid/sleeved version if you're having trouble with your frame creaking.