Shimming Skate Axles to 8mm
Why do we need to shim skate axles?
Due to manufacturers keeping the cost of manufacturing truck to an absolute minimum and make truck easier to service after some abuse, truck axles are undersized 5/16" shafts.
The problem is that 608 skate bearings are designed to fit an 8mm shaft. On average axles will be 0.004" (dia.) less than what the 608 bearing's 8mm bore requires,0.3149".
How to we make the shims
usually, .0010-.0020" stainless steel shim stock cut to .951" long x.977" wide works well). Curling the shim over the back side of some sissors makes it easier to get the bearing over while holding the shim on the axle.
What kind of performace gains will this achive
In addition to longer bearing life and the ability to properly tighten the axle nut, a shimmed axle will result in a faster roll and more controlled slides.
When a skate wheel has been properly installed, the axle nut is fully tightend to proper torque and a very slight amount of play is felt in the wheel. This play will be play within the bearing itself rather than over the axle. Free spin may not be great, but free spin is not a valid test of proper installation of a skate wheel.