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Misfit Psycles
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Anyone heard tell of an eccentric bottom bracket for use in standard shells? Rumour has surfaced but i am struggling to understand how they can match the tensioning properties of an eccentric BB shell or sliders...external bearings rotating with the axle??? teenier tinyer bearings?

Anyone heard same? Anyone? BS?
 

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Doesn't seem possible, if it is, doesn't sound like anything I'd use.
 

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nogearshere said:
Anyone heard tell of an eccentric bottom bracket for use in standard shells? Rumour has surfaced but i am struggling to understand how they can match the tensioning properties of an eccentric BB shell or sliders...external bearings rotating with the axle??? teenier tinyer bearings?

Anyone heard same? Anyone? BS?
Actually sounds quite doable with an external bearing setup, its not like we use the outer chainring mount and could even use the inner ring mount if we had to.

The debate will probably center around Q factor, creaking, and possible damage to the BB threads.
 

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Ratt said:
Actually sounds quite doable with an external bearing setup, its not like we use the outer chainring mount and could even use the inner ring mount if we had to.

The debate will probably center around Q factor, creaking, and possible damage to the BB threads.
doable? OMFG

let's see:

normal bottom bracket shell inside diameter is ~33.9mm

count in the fact that your EBB external bearing cup needs to thread in there, you lose at least 3mm diametrically

now, the EBB needs to provide full 1" (25.4mm) of adjustment. therefore the spindle axis will be sweeping a circle of at least 1" diameter.

what does that leave you for spindle diameter? (33.9-3-25.4)*2=11mm

a regular square taper spindle (~17mm) will beat that by a long shot.

to use a regular square taper spindle in this setup, the most adjustment you can get is 19.4mm (about 3/4" for the metrically handicapped)

besides, having the bearing mounted way out (essentially half of the bearing is hanging in the air, only supported by the cup, not by the BB shell outer surface) will do short work of bearing life span.

besides besides, remember that unlike the EBB shell, the two bearings supporting the spindle are independent of each other and can move in different directions. when you pedal, the torque in the spindle will tend to move these bearings in opposite directions. talk about stiffness. eh.

besides besides besides, how are you going to fix the bearing in place? set screws? internal expansion? whatever you use, to fix the bearings in place tight (so that you get reasonable amount of stiffness in teh system), it basically forces your bearing cup to be VERY deep, your spindle will stick WAY out.
 

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weather said:
doable? OMFG

let's see:

normal bottom bracket shell inside diameter is ~33.9mm

count in the fact that your EBB external bearing cup needs to thread in there, you lose at least 3mm diametrically

now, the EBB needs to provide full 1" (25.4mm) of adjustment. therefore the spindle axis will be sweeping a circle of at least 1" diameter.

what does that leave you for spindle diameter? (33.9-3-25.4)*2=11mm

a regular square taper spindle (~17mm) will beat that by a long shot.
Yeah i figured with so many people still using square taper that this amount of flex would be acceptable, could even have it taper up to ISIS

to use a regular square taper spindle in this setup, the most adjustment you can get is 19.4mm (about 3/4" for the metrically handicapped)
Didn't think it would that much was only looking for 1/2" and ya a halflink would be involved.

besides, having the bearing mounted way out (essentially half of the bearing is hanging in the air, only supported by the cup, not by the BB shell outer surface) will do short work of bearing life span.
Didn't think this would be an issue, don't engines use bearing caps? But if you are an M.E. i will take your word for it.

besides besides, remember that unlike the EBB shell, the two bearings supporting the spindle are independent of each other and can move in different directions. when you pedal, the torque in the spindle will tend to move these bearings in opposite directions. talk about stiffness. eh.
Was thinking cartridge BB with a lockring or taper lock or both on the other side

besides besides besides, how are you going to fix the bearing in place? set screws? internal expansion? whatever you use, to fix the bearings in place tight (so that you get reasonable amount of stiffness in teh system), it basically forces your bearing cup to be VERY deep, your spindle will stick WAY out.
Yeah Q factor will be a factor and I was wondering if internal expansion will just crush the BB threads or if rubber or plastic used as a cushion would just creak although current X-Type BB uses plastic between the bearing and spindle.
Was just thinking a small EBB to fit inside a regular shell done with a 11mm-17mm spindle and needle bearings or external bearings.
 

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wont work.

stiffness of a spindle roughly scales as the CUBE of the diameter. a 11mm spindle would be about 27% as stiff as a regular 17mm spindle. your external BB and ISIS and octalink do not even claim a 400% stiffness increase.

it doesn't matter if you taper it up or not, flex in the middle section of the spindle is all it takes to make noodles of cranks. sitffness of the entire setup is only as stiff as the least stiff part of it.

bearing life is a huge issue. bearing caps do not work when your bearings are swinging on the OUTSIDE of the support and you are adding torque orthogonal to the spindle axis.

i AM talking about cartridge BB. the two bearings are still independent of each other. think about it--your bearing cups are MUCH larger than the shell, how the hell are you going to join them together thru the shell? you simply do not have anything that rigidly hold two bearings in place at the same angular position (which, once released, needs to be able to move freely to provide adjustability). a regular BB has its own shell PLUS the BB shell to do this. a regular external BB has the cup and the side surface of the shell to do this since everything's symetric.

remember that you don't have much space inside the shell to play with. other than the spindle, you can't fit ANYTHING inside the shell. as far as BB goes, any bearings--ball, needle, whatever--will require at least one race to roll on (the spindle serves as the other). and that race needs to have a certain thickness. that's simply too much for the little space you have.
 

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weather said:
wont work.

stiffness of a spindle roughly scales as the CUBE of the diameter. a 11mm spindle would be about 27% as stiff as a regular 17mm spindle. your external BB and ISIS and octalink do not even claim a 400% stiffness increase.
Like i said people seem to find square taper acceptable in terms of flex

it doesn't matter if you taper it up or not, flex in the middle section of the spindle is all it takes to make noodles of cranks. sitffness of the entire setup is only as stiff as the least stiff part of it.

bearing life is a huge issue. bearing caps do not work when your bearings are swinging on the OUTSIDE of the support and you are adding torque orthogonal to the spindle axis.

i AM talking about cartridge BB. the two bearings are still independent of each other. think about it--your bearing cups are MUCH larger than the shell, how the hell are you going to join them together thru the shell? you simply do not have anything that rigidly hold two bearings in place at the same angular position (which, once released, needs to be able to move freely to provide adjustability). a regular BB has its own shell PLUS the BB shell to do this. a regular external BB has the cup and the side surface of the shell to do this since everything's symetric.
In a cartridge BB both bearings are held in the same shell so they will not swing indepedent of each other like in a cup design. Ya was thinking one side would have to have the bearing installed after the fact and held down with a "bearing cap" of some sort.

remember that you don't have much space inside the shell to play with. other than the spindle, you can't fit ANYTHING inside the shell. as far as BB goes, any bearings--ball, needle, whatever--will require at least one race to roll on (the spindle serves as the other). and that race needs to have a certain thickness. that's simply too much for the little space you have.Ya this will not be durable at all, but hey there are plenty of ISIS users out there who still use the format, it's durable enough for someone.
I am not an engineer so I have no idea if it will work but have played with BBs where the bearings slip fit both in bearing cups and on the spindle and stayed creak free. Installed BBs where the bearing preloads and end play was set using an elastomer ring and the spindle resting on plastic and got no side play from that. It just strikes me that a press fit or a super high level of precision is not necessary in BB just durable bearings.
 

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k, here's a VERY crude model.

68mm BB shell, 33.9mm ID
standard 17mm spindle
standard 6003 bearing, 17mm ID, 35mm OD, 10mm WD.
175mm crank arms
insert is 55mm OD.

as it is, the assembly provides barely enough adjustment (13mm) to be used with a half link.

discuss.

 
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