Your shock’s remote reservoir is not there for cooling!
Updated: Dec 5, 2021
With this post, I am starting a series that will be a crossover of ‘Myth Busters’ and ‘How Stuff Works’. You can also contribute by suggesting topics that you want to get covered or clarified. Send me your suggestions! Thanks.
I have heard this claim: ‘A big benefit of the remote reservoir is the added cooling’ for so long, I can’t even remember the first time somebody mentioned it. I want to yell from the roof tops: ‘Your shocks’ remote reservoir is not there for cooling!’
Don't get me wrong, reservoir shocks are better in many ways, but what I want to point out is, that the cooling effect of a reservoir is so minimal that it should not be listed as a feature.
In the internet information age we live in now, you would think it’s easy to YouTube information on that topic and educate yourself. Unfortunately, that is not the case, because the myth goes strong with devout followers that keep reiterating the same story over and over again. The problem I found is, that everybody and their grandma is giving ‘sound technical advice’ on the benefits of upgrading to remote reservoirs, but (usually) don’t have the technical background to fully understand what they are talking about. Claims are made without any explanation or supporting information. It appears that mostly Retailers and Offroad/Overlanding Personalities align on that side, and the real experts like Race Shops and Shock Builders are on the other. Hundred thousand of followers vs. a few thousand followers. Who do you think gets their information out, and who is actually correct?
Let’s get back to the very basics and check into the physics of it. Once we understand that, the answer becomes pretty clear.
The pic below shows the build of a typical remote reservoir shock.
If you look at the image and specifically the position of the floating piston in the reservoir, this is very much representative of all shock setups. You can see that the reservoir is mostly filled with nitrogen. Even with the shock shaft all the way compressed, the reservoir would only fill up to about half, ... maybe.
Now let’s compare the size of the reservoir to the size of the shock body:
Taking the top and bottom cap into account, I think it’s fair to say that the reservoir is half the size of the shock. Putting these two pieces of information together, I overlaid the rough oil level in this following picture:
It should become clear now, that the increase of surface area, where the oil could dissipate heat to the surrounding, is negligible, somewhere in the range of 10%. To express it differently: If your shock burns up 60 minutes into a wild ride, the reservoir shock would have potentially survived 6 minutes longer. This is not an improvement that would be worth the effort (complexity) and cost of the reservoir. This is not why remote reservoirs are mounted to shocks. The same cooling improvement could be achieved by mounting a little deflector that guides air onto the non-reservoir shock.
Another argument that needs to be debunked is that the increased oil volume of the reservoir shock cooling. This one is easy to explain and my favorite analogy to that is boiling water. Imagine a pot with 4 gallons of water and you bring the water to a boil. Now increase the amount of water to 5 gallons and try to bring it to a boil again. It will still boil. Increasing volume does not keep it from boiling, or in shock terms, more oil does not keep the shock from overheating.
And lastly, I want to take a look at it from a different point of view. If it would be required to increase heat dissipation, the first go-to would be to effectively increase the surface area by installing a ‘heat sink’. The surface area of a shock heat sink is about 4-5 times that of a smooth body shock. Now that is a real difference.
Applying the flawed logic of the 'cooling feature of reservoirs' to other aspects of the shock, one might rather install 25% longer shocks, because they have 25% larger surface area for cooling (compared to the 10% of the reservoir). I think you get my point, why cooling is not a real feature of the reservoir.
In conclusion, unless your shocks look like this:
Your remote reservoir does nothing for cooling!