Want to fit a 386Evo on to a Pressfit BB

godtabh

Totally confused about this.


I have a pressfit BB with hollow tech 2 crank set. I want to put on a FSA group set with a 386Evo spindle.

What BB adaptor do I need. Very confused

at1withmyself

godtabh wrote: »

Totally confused about this.


I have a pressfit BB with hollow tech 2 crank set. I want to put on a FSA group set with a 386Evo spindle.

What BB adaptor do I need. Very confused

A new bottom bracket is needed;

https://www.wiggle.co.uk/prime-bb386-bottom-bracket-sram-dub

Unless your current BB has the reducers installed fir the hollow tech chainset, then simply remove/swap them out fir the 30mm chainset on the FSA group.

nilhg

at1withmyself wrote: »

A new bottom bracket is needed;

https://www.wiggle.co.uk/prime-bb386-bottom-bracket-sram-dub

Unless your current BB has the reducers installed fir the hollow tech chainset, then simply remove/swap them out fir the 30mm chainset on the FSA group.

That BB is for a SRAM dub crankset with 29mm axle, won't fit the 30mm on the FSA.

OP what BB is in the bike already? Once you know that you can use the wheels manufacturing finder to work out what you need

https://wheelsmfg.com/bbfinder

at1withmyself

nilhg wrote: »

That BB is for a SRAM dub crankset with 29mm axle, won't fit the 30mm on the FSA.

OP what BB is in the bike already? Once you know that you can use the wheels manufacturing finder to work out what you need

https://wheelsmfg.com/bbfinder

Well spotted, didn't realise there was a 29mm diameter as well as the 30 and 24. It's a shame they can't just agree a standard and stick with it!

godtabh

It’s an SM BBR60 bottom bracket. Now to research it.

Paul Kiernan

godtabh wrote: »

It’s an SM BBR60 bottom bracket. Now to research it.

Now you're even more confused because that's a threaded BB, not a pressfit!

MisterSpaccato

godtabh wrote: »

Totally confused about this.


I have a pressfit BB with hollow tech 2 crank set. I want to put on a FSA group set with a 386Evo spindle.

What BB adaptor do I need. Very confused

Please don't do that. Shimano pressfit shell has a diameter of 41 and uses 6805 bearings that have an outer diameter of 37mm and inner diameter of 25mm. Now if you want to fit a bigger crank spindle in the same shell you can't touch the outer diameter, because that's determined by the shell width, so the only way would be using smaller bearings. There are 6706 bearings that have OD of 37 and ID of 30, but loading such tiny bearings with the weight of a human body plus the radial and rotational forces involved in pedaling (imagine standing on the pedals while climbing a steep hill) is a really bad idea. Look at the load ratings of the two different bearings for comparison:

Basic Load Ratings

6805
Dynamic: 4,36kn
Static: 2,6kn


6706
dynamic: 1.14 kN
Basic: 0.95 kN


This would bring accelerated wear, and the possibility of a creaking bottom braket.



To compensate for weak bearings, WheelsMFG thought of making custom sized bearings with two rows of balls, that are pressed directly in the frame: https://wheelsmfg.com/bb86-to-30mm-flanged-dual-row-pressfit-86-92-abec-3-bottom-bracket.html


There are no load ratings reported on the spec sheet, and i wonder what is the friction compared to standard bearings with a single row of balls with larger diameter, but my guess is that the latter is better. Also, the nylon casing used for regular pressfit bearings has a tiny bit of flex to compensate for any irregularity in the frame, so unless your frame is absolutely perfect, you might incur in misalignment issues.


Please stick to 24mm crank axles if you have a pf86 shell. 30mm crank axles are a solution to a non existent problem, but if you really want to use them, switch to a frame with BB386evo or T47, that have a bigger outer diameter and can therefore house bigger bearings.

at1withmyself

Paul Kiernan wrote: »

Now you're even more confused because that's a threaded BB, not a pressfit!

Wouldn't that mean the current one is 68mm width whereas a 386 would be 86 wide?

Can you confirm if its threaded OP and also can you measure the width of your BB shell on the frame?

nilhg

godtabh wrote: »

It’s an SM BBR60 bottom bracket. Now to research it.

https://r2-bike.com/KCNC-Bottom-Bracket-BB386-EVO-Adaptor-for-BSA-68-mm-black

Or something similar from someone like Wheels Manufacturing or Rotor

MisterSpaccato

I don't understand if OP has a threaded or pf shell, but in both cases it's a bad idea to use a 30mm crank in a bb shell only marginally wider than the crank itself. I've already exposed my reasons for the use case with pf bb, for threaded the discussion is similar, since the BSA shell has an inner diameter of 33.6–33.9 mm and the crank is 30mm wide, this means that the threaded part of the bearing cups that secures them to the frame will end up being only 1.8-1.95mm thick.

nilhg

MisterSpaccato wrote: »

I don't understand if OP has a threaded or pf shell, but in both cases it's a bad idea to use a 30mm crank in a bb shell only marginally wider than the crank itself. I've already exposed my reasons for the use case with pf bb, for threaded the discussion is similar, since the BSA shell has an inner diameter of 33.6–33.9 mm and the crank is 30mm wide, this means that the threaded part of the bearing cups that secures them to the frame will end up being only 1.8-1.95mm thick.

The bearings on the threaded BBs are outside the frame so can be built to a decent spec, space is not as limited.

Edit: sorry just seen you were referring to the threaded section of the BB, valid point