Shock mounting positions

I swear, this is the most confusing and least understood part of RC car tuning.  I’ve spent a lot of time reading about shock positions and tuning and thinking about what is actually happening, and came to the realization that there are two things going on that are often confused, but actually having separate effects.

For the shocks (front or rear, it doesn’t matter), there are obviously different holes on the shock tower that you can mount them to, and also different holes on the arms that you can mount them to.

Ignore all of that for now, it’s more important to internalize two concepts:

1. Laid down vs. Upright shock

A laid down shock has a more progressive spring and damping characteristic.  When it’s more horizontal, the shock starts out soft and then builds up towards firm as it gets compressed.  That’s because the angle is changing as it is being compressed and starts out horizontal and moves towards more vertical.

A more vertical shock acts more linearly and tends to be more medium-firm the whole stroke through.

2. Shock spaced closer or further from the fulcrum (hingepin)

If you look at the way the arm and shock is designed, it is basically a mechanical lever.  The hingepin is the fulcrum, and the arm moves towards the shock tower as the car rolls in a corner (well, the shock tower is actually moving towards the arm, but it’s the same thing), or as the wheel deflects from bumps and jumps.

The closer the shock is mounted to the fulcrum, the more leverage the arm has on the shock and so it will feel softer.  The further away the shock is mounted, the less leverage it has and the shock will feel more firm.  Now I’m talking total spacing, moving the entire shock (both top and bottom) towards or away from the fulcrum.

With that out of the way, you’ll realize that when you change a shock mounting position, you’re actually affecting BOTH of these concepts simultaneously.  It’s very difficult to lay the shock down more without moving it closer or further from the fulcrum.  When you move the top shock position inward on the shock tower, you are both laying down the shock more AND moving it closer to the fulcrum.  Similarly when you move the bottom shock position out on the arm, you are laying down the shock more AND moving it further from the fulcrum.

It’s very difficult to isolate only one of these factors, as moving a shock position will change both things.  Theoretically, you could simultaneously move the shock in on the tower and out on the arm, which would lay it down more and make it more progressive, but keep the overall shock position roughly the same and keep the same overall stiffness.

This is the first time I think anyone has tried to explain what is going on.  Usually they just say “doing X will make the shock softer” or “doing Y will make it harder”, but almost every time someone says that, they completely contradict what someone else says.

Hopefully this post clarifies some of that confusion.  It was seriously an amazing moment of clarity for me when I figured it out.