Inside the rim, there is a spacer/tube that is the diameter of the axle. What is the purpose of this thing? It is not to space the bearings as the bearings seat on machined surfaces of the rim. The only thing I can think of is that they make putting the wheel on the axle easier.

Please explain the purpose of these?

 

The spacer is for the bearings and the wheel. The wheel is made of aluminum and with the amount of torque that is applied to the axle nut, it will easily deform the rim. The inner race of the bearings get squeezed against that steel tube.

 

Thanks. About 10 mins after I posted this, I dug up a post on the Suzuki board that explained its purpose (which was a "duhhh...I should have seen that" moment after I read it). I would have come back and deleted the post but got sidetracked.

The purpose of the spacer is really to keep from destroying the bearing, not the wheel (the bearing would go long before the wheel). Radial bearings do not handle thrust loads very well at all and the torque of the axle nut will drive the inner bearing races towards each other. Therefore, by having a spacer in between the two bearings, the axle nut sees on large "spacer" spanning from nut-to-axle head. Thus there is no thrust load from the torquing of the axle nut.