Man, for 90% of general RC use, rubber shielded is the way to go. Yeah, metal shields can have less friction, and so can Teflon, but I'm not willing to do the extra maintenance on a runner, especially if it's one that gets run hard frequently. Now, on a stock class race car, I can see the benefits of bearing tricks.

Shielded bearings vs sealed bearingschart

For my konghead, I intend to do a mixed setup. Metal for anything inside a gearbox as this is sealed anyway. And rubber for the driveshafts at wheel side.

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Doubleshieldedbearing

Rubber better suited to off roaders etc that get really wet. I have to say I dont know if theres buch benefit for internal bearings sugh as gearboxes etc? but drive shafts uprights etc their good. I tend to use rubber jut in case. My Stadim Thunder was running through puddles etc to day so worth it. Same price I think, at least they are from rcbearings.co.uk

There are also some bearings around nowadays, which have a metal shielded side and a rubber sealed side. They are intended for racing, to get the protection and the lowest possible resistance. Quite nice for wet races.

Rubber sealvsmetal seal bearing

Shielded bearings vs sealed bearings vsseals

Being new to the hobby I have been buying Metal shielded bearing thinking metal must be better than rubber BUT am surprised the amount of time people suggest rubber shielded bearings

When it has absolutely no oil and no grease, it even works like a ceramic bearing. (But that's bad)  You can stick a 5mm shaft and turn it, it literally turns for 60 seconds.  But no oil means the bearing will wear out really fast.  So I use light machine oil.  If I didn't, as bearings wear down, pinion gear will push spur gear farther, and gears would wear too.  If you remove grease, light oil is a must.

With 18 "naked" bearings on the inside, my fingers can turn one drive cup. All 6 drive cups would turn for almost 1 second (with diff clay). That sounds like nothing.  But with this many gears, + grease on the teeth, 1 second is a lot.  (I use Labelle 106 Teflon grease -above- to reduce friction between teeth too)

Doshielded bearingsneed to be greased

But Konghead and Dynahead use 40 to 70 bearings.  For these, some bearing-planning could pay off.  Small friction on each bearing adds up 70 times.

Which is why I use naked ball bearings only in the gearbox. (I seal the gearbox with plumber's grease to make it almost waterproof)  If there is no dust, no shield is fine.

Open bearingvs sealedbearing

Rubber shields are easier to remove.  I take the shields off and re-lube them for the internal gears.  I leave shields for outside.

The rubber shield makes tight contact outside race. There is tiny gap with the inside race. There is some drag.  Metal shields, however, cannot make contact either races. If it did, the bearing won't turn.  So there are larger gaps. Tamiya uses thick grease to block the gap.  Below is how much I could scoop out from.  It's from 1 side after taking off the metal shield (from one 1150 bearing).

Why bother doing this for a simpler car like the Hornet?  It has only 3 gears.  As long as it's got those 13 bearings, it should be fine.