Revisiting Micro Bearings
The most commonly used bearings in inline skates are 608 bearings, which have 8mm holes, 22mm diameter and 7mm width. However, fitness and speed skates nowadays come with an option for 688 micro bearings. These bearings – also with 8mm holes, but smaller outside diameter and narrower width than standard bearings – help reduce the overall weight of skates, making them faster and more comfortable.
Above: 688 and 608 bearings – side by side
Why 688 Micro Bearings?
1. LIGHTER
688 micro bearings weigh an average 70% less than a standard 608 bearing.
2. QUICKER ACCELERATION
688 micro bearings let you take off faster.
3. LESS ROLLING RESISTANCE
688 micro bearings’ 9-ball design allows for better weight distribution on two balls over one, giving you more glide for your stride.
If you’re using regular skate wheels, you can convert your 608s to 688s with special nylon adapters and extra long metal spacers. You can also change your wheels to those with smaller hubs suitable for use with micro bearings.
MicroBearing Spacer
Above: Spacers
Above: Bearing spacer and hub assembly (Source: SkateFAQ)
There are basically two types of spacers for use with micro bearings – short-sleeved spacers and long floating spacers (see Pic 2). Spacers should be exactly the same length as the center of the wheel hub (the small section in the middle of the wheel that keeps the bearings separated, see Pic 3)
Long floating spacers are required with 8mm diameter axles (common in speed and higher-end fitness skates with aluminium / alloy frames)
Short-sleeved spacers are used with 6mm diameter axles (common in recreational skates with plastic-nylon composite frames, or in aluminium frames with rockers)