dont know if this is old news or whatever but it's just something i've recently found and fixed with my car:

i found my losi was damaging bearings pretty bad, motors were over heating and was having to under gear them severly etc. just excessive friction in general.

which i tracked down to the hex/axle/bearing area.

tried different oils for the bearings, running extra spacing between the bearings thinking they were being pinched due to there not being enough spacing between them, also not tightening wheels down too hard (leads to wobbly wheels anyhow), etc. but it still keept happening.

finally worked out that between the hex and the shim between the bearing and the pin for the hex that they were pushing the hex out over the threads and making it easy to overtighten and pinch the bearing.. or i guess even cornering loads on the track could also have a greater effect on the bearings.

to fix i took out the shim and used a thinner shim from LOS6230 Losi, SHIMS ASSORTMENT (20) 2.50.

just something to look at, especially if you find your hub bearings bind up as you tighten your wheel nuts.