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RC OBSSESSION

Upside Down Shocks

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usd_shock_2.jpg

One of the things I like best about the exciting hobby of R/C cars and trucks is the endless opportunity to experiment with the vehicle in order to achieve an ever higher level of performance.  I find that in pursuit of this objective one must often ignore the way things are normally done and consider everything and anything, no matter how radical.

For example, shock absorbers on R/C vehicles are always (as far as I know) mounted ‘right side up’. Why??  Is it because it looks ‘normal’ that way?  Is it wrong to mount them upside down?  I began to wonder about this while looking at my truck one day. What are the possible benefits of mounting your truck’s shocks upside down and would these benefits outweigh the negatives? Let’s find out.

First off, is it really so unorthodox to mount shocks upside down? Surprisingly, the answer is ‘no’. Many motorcycle manufacturers mount shocks upside down, especially the shocks on the front forks.  With all the R&D at their disposal, they must know something advantageous about mounting shocks upside down.  Sure enough, a significant advantage exists – a lower center of gravity.

Like all monster trucks, the E-Maxx has a high center of gravity.  Being electric, its center of gravity is even higher due to its two heavy electric motors and two very heavy battery packs. These items conspire to make the E-Maxx very top heavy.  Add to this the weight of the shock bodies, which are fluid filled, and mounted way up high.  Not good. By mounting shocks upside down, the truck’s center of gravity is lowered. In fact, it’s lowered enough that you’ll notice a small but appreciable difference when cornering at high speed. To me, this is a big positive.

The next advantage is your shocks will leak less fluid.  Let’s face it, all R/C shocks leak. Why? The shaft seals are imperfect and become more imperfect with every stroke. As the fluid leaks out, air leaks in. This air pocket, which of course resides at the top of the shock, creates an undampened area within the shock body. When the piston passes into the bubble, all dampening disappears.  This loss of dampening occurs right at the worst spot – when the shock is reaching full compression (think coming down off of a big jump) that adds to the risk that the truck will bottom out.  Mounting the shocks upside down largely eliminates the leaking of shock fluid and it moves the air bubble to the other end of the shock (relative to the piston).  With the shaft seals now at the top, their slow trickle of fluid being drained due to gravity is eliminated. Additionally, as the shock compresses, the piston is now moving down and away from any bubble.  Therefore, there is no way that you will loose dampening under compression. True, there is still a seal at the bottom of the shock (the cap seal), but because this seal is much tighter than the shaft seal, fluid is less likely to leak out (mine have never leaked).

Shocks Mounted Upside Down

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Another advantage is that the shocks don’t need to be removed in order to change the springs. Simply remove the shock mounting screw from the shock tower and you’re good to go. I change my springs frequently depending on conditions so this is a real advantage.

Yet another advantage is the shafts are somewhat removed from the debris kicked up by the wheels.  Less debris and grit sticking to the shaft means less wear of the shaft and seals.

So you might be asking yourself, with all these advantages are there any disadvantages?  So far I’ve only been able to come up with three.

First, your unsprung weight is increased.  In very general terms, sprung weight is any weight that is not part of the suspension. The less unsprung weight you have, the smoother the vehicle will ride and the more responsive it will be. For an example, suppose  a car’s unsprung weight is increased by filling it’s tires with cement….how would it handle? You get the idea.

But let’s think about this for a minute. On a real truck, the unsprung weight comprises about 8% of the vehicle’s total weight.  On the E-Maxx, the unsprung weight is much higher, maybe 20%. So a little increase in the unsprung weight will make a negligible change in the way the truck handles. Consider this, shocks, because they attach to sprung and unsprung components of the truck are partly sprung and partly unsprung so turning them over doesn’t add as much unsprung weight as you might think.

A second disadvantage is that your shock body, instead of its shaft, is in the path of debris kicked up by the wheels.  But is it really in harm’s way? I don’t think so.  If you look at the assembly, you’ll see that the top A-arm offers a large degree of protection.  Either way you look at it, one end of the shock has to be at the bottom.  I think the shaft is the more delicate end so it’s better off on the top. I’ve been running my shocks upside down for quite some time and they have yet to receive damage that would’ve been avoided by mounting them right side up.

Lastly, you may have to remove a little material from you lower A-arm’s shock mount to improve shock cap clearance. I use RPM A-arms and this is only an issue if you are using the middle or outer shock mount.

With the pros and cons in mind, what do you think? Why not give it a try and see if you like it. One last benefit, you’ll draw a lot of attention from your buddies next time they see your truck.  They may notify you that you installed your shocks upside down, but after you tell them why they’re upside down and they see how your truck handles, don’t be surprised if they mount their shocks upside down too!

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