Inv4drZm
Senior Member
Yes, external reservoirs do "just house extra oil" and they are not more complicated than that. You're talking about dampening adjusters, which are an added feature that can be built into them at extra cost. It'd be correct to say that external reservoirs enable you to add dampening adjusters, but it has nothing to do with the reservoir itself.
There's pro's and con's to everything. If you really need the increased cooling capacity an argument could be made for finely-tuned external reservoir coilovers* without adjusters due to the increased heat generated by that second shim stack. Again it's application specific.
What I'd like to to know is why performance street coilovers are built with adjusters in either the base or top of the shock itself, but I'd wager it has something to do with the heat generated in offroad race conditions and overall size and space limitations.
They all have pistons in them, even the non-adjustable reservoirs.
Cooling capacity is increased not only because of the increased oil volume but also due to the increased surface area the oil is in contact with inside the body and remote reservoir.
As for ride or tunability I've found online that by having more oil in the body of the shock, it leads to less oil cavitation. The gas chamber could be larger in the resi but I'm not sure what benefit that is.
https://www.race-dezert.com/forum/threads/how-does-a-remote-reservoir-shock-work.83993/
It must not be possible to add an adjuster to a non-resi shock because there is no orifice for the oil to flow through.