Hi all,
Bearings with ceramic ball compliments give no performance increase with regard to load (they actually have a reduced dynamic load rating compared with steel balls). They are only normally used in industry to increase the bearings upper speed limit. They tend to have slightly better resistance to lack of lubrication.
I would recommend that bearings with metal shields are checked for noise and regularly cleaned with solvent and soaked overnight in a standard mineral oil.
If the bearings have an internal teflon coating then this will help with lubrication however will not gaurantee quality. Most bearings supplied for use in rc cars are not manufactured by the recognised top quality bearing manufacturers but are certainly 'fit for purpose'. Especially considering the relatively low prices that are charged.
If possible I would opt for bearings that have rubber contact seals with grease lube rather than the usual non-contact metal shields.
The biggest bearing killers are contamination from dirt and dust - which leads to fatigue damage and lubrication failure and also axial loading. Check that shims (like those on the diff outdrives and the main bevel gear shaft) are not placing the bearing under too much thrust loading.
Hope this helps a little.
