Why 2 swinging arm bearings ? Why not a single larger one ?

[Blambo]

Hi, (when I say larger in te title, I meant longer. Sorry, it's been a long, cold day in the garage trying to get her back on the trail...

My Pampera has 2 bearings on each side of the swinging arm, HK2020 + HK2010.
Looking at the parts fiches, GasGas seem o do this a lot on several models.
But why ?
A single HK2030 fills the exact same space as the 2 bearings fitted, 20mm + 10 mm = 30mm
So can't I just use the one, longer bearing ?
Mike in England

[Zman]

That is a good question! My first guess is that it is less expensive to run two smaller bearings or it is easier to assemble the two. Were the factory ones pushed together or did they have a gap between them to provide a backer for the seals?

[Blambo]

They are pushed together.
The total length of the 'tube'/hole in the swinging arm is 39mm.
That's 20 + 10 of bearings and two 4mm seals with 1 mm spare so the seals don't get rubbed by the movement.

There is no gap between the bearings.
Mike

[barossi73]

Im goin to guess to allow for twisting/flex across the swingarm.purely guessing,i really dont know
Id assume any twist flex across would be smallish but
imagine a bike sliding sideways then the rear grips,twisting force on axle pushes inside arm up,pulls outer arm down relative to each other.has to be flex somewhere?
Perhaps 4 smaller bearings drag less when twist happens.(right before the highside!)
Allowing some flex in hard cornering would allow the tyre to 'stand up' slightly,keeping off the edge slightly and perhaps finetuning understeer/oversteer characteristics.

[barossi73]

What im trying to say is id put it back the same but newer!(bad red wine)

[Zman]

I understand what you are getting at but I don't see the hardened steel collars, swing-arm, pivot axle and bearings flexing too much.

As I recall one of my Yamihaha dirt bikes had longer single bearings in the swingarm. I myself would not hesitate to try the longer bearing. The longer bearing will handle load better because you have more contact area than two bearings back to back because of the gap in the middle being open.

[swazi_matt]

It is the same bearing they use in the linkage as a single bearing so maybe it has something to do with GG love of standardizing everything on their bikes.... Bwah ha ha haha ha ha!!!

[barossi73]

I tend to agree on a dirtbike zman,it was a wine fueled guess based on moto gp where theyre always testing swingarms and chassis with different flex characteristics.
You would expect the flex to be mainly in the arms,not across the axis,so were back to guessing!
Perhaps 2 bearings allows a smidge more grease to be packed in there?

[pscook]

Originally Posted by swazi_matt

It is the same bearing they use in the linkage as a single bearing so maybe it has something to do with GG love of standardizing everything on their bikes.... Bwah ha ha haha ha ha!!!

I believe you are right, it's an economy of scale. Is it cheaper to keep one bearing in stock, or two types? From a manufacturing standpoint, always go with the cheaper and easier option. Single source, single part number, no questions beyond quantity. It might be that two small bearings are cheaper (from their supplier) than one double length bearing.

[5valve]

You can easily use single longer bearing. It uses double inner race, so they move independently, if one gets hooked, you still have movement.
Your vice or press should allow greater span also.

I used this type of bearing instead of doubles in yamaha linkage, with some modification, since yamaha uses non standard bearings.
I think I used doubles in my gas application, maybe cost or availability at the time was the factor, don't remember.

Must note, that non original bearings like INA HK**** use smaller D needles and less of them, while original koyo use cageless design, with needles touching eachother.
Forcewise, koyo should withstand greater torque, but in reality, INA does just fine.