The "NLGI consistency number (sometimes called “NLGI grade”) expresses a measure of the relative hardness of a grease used for lubrication".
How much grease should I use to pack hubs? Should I use just a tiny bit, as in the left of the figure? Here I'd use just a minimal amount to coat the surfaces.
Or should I pack in as much as I can, as on the right of the figure?
I suspect that racers and those who really care about getting an extra 1% of performance should, before a race, though not necessarily to practice:
- use a minimal coating of grease, and
- use a grease of low NLGI, perhaps even "000", one similar to cooking oil.
While the rest of us, who:
- do not race,
- do not care about a 1% reduction in performance due to viscosity, but do care about a 10% reduction, and
- who do not want to overhaul the hubs all that often
- use a maximal amount of grease, especially to make it possible to wash the bike with just the mildest of water jets and not fear water ingress, and
- use grease with NLGI between 2 and 3, such as marine grease, one that will last the longest.
Is this about right?
- If you're curious how the ball bearings can last, given the point-to-point contact, which would mean that the stress at the point would in theory be an infinitely large value, head on over to engineering.SE.
- When riding a bike, we are constantly and unconsciously doing micro-steering adjustments to stay upright. These micro adjustments make the ball bearings rotate inside the hubs, which means that the ball bearings get to distribute the load over the entire surface area, whereas the axle hubs and the cones get the stress in just one continuous band of limited area. Moral of the story is this: you are likely to need replacing the axle and the cones before you need to replace the ball bearings.