Shocks and what are we doing with them to tune? Its one of the (we think) over looked areas for many. For most its a simple question of what springs do I want and what oil are people using. Like many things in tuning this is something that may not work the same for everyone. One small change for some may be the difference between progress or not making a gate.
Something we always say is ”opposite corners work together”. What do we mean by that?
With all the different chassis’s out there you tend to see many options for shock locations. From vertical to virtually flat, what works the best for you can take a little tuning time but is worth it. So heres a little insight to how we see things.
A shock is most effective when its perpendicular to the lower links and the arc they create on suspension travel. But in rock crawling where we need our axles to articulate, vertical/perpendicular can put limits on that. We need our springs to be balanced front to rear and our oils to help control the transfer of weight.
As the picture above shows the further you lay a shock down the less you use of its effectiveness. In easy terms a shock will begin to feel softer as you lay it down. You begin to ‘pivot’ on its chassis mounting point, the shocks fulcrum. Idealy we want a Linear feel to our shocks as opposed to a rising/falling feel to its movement.
Laying a shock down will generate a falling feel. Meaning as you compress the shock it feels stiff at first but then begins to feel softer, falling in resistance. When you lay your shocks down too much you may feel how they just collapse on you at some point. This is what we dont want, we are using less of the spring and oil. We call that the point the shock ‘cams out’ meaning you are no longer using the shock and simply just rotating on its chassis mounting spot.
So how do we find that point? Granted with all our years of experience we pretty much know our go to springs and base point for shock oils but let us try to explain how we got there.
Lets build all 4 shocks with the same springs and NO oil first. Now mount them to your chassis in the middle hole of what you have available. This will give us angles to play with for adjustments.
First we will use SCX shocks for this, or any shock body that is threaded for preload adjustments. Put all 4 springs on and fully extend the shock shafts all the way out. At this point adjust your collars down to just touch the springs. We dont want to put any preload on them, this will cause our balance to be off. With the shocks on the truck and the truck in RTR (electronics/battery/wheels on) condition just drop it from about a foot off the ground/bench. We want the truck loaded with everything to drive it and let it sit at normal ride height. Light weight trucks may need to be pushed down and let it come up to ride height.
Side note – this can also be done with Traxxas/Dravtech type shocks. Simply put your spring on with no preload o-rings and extend the shock shaft. Add just enough o-rings to make up the difference in spring to shock body. The idea is you want the least amount of preload on your spring as possible.
Now pick up one wheel (we’ll say the front) and watch how its shock collapses while also watching the opposite corner shock. Example, lift the left front and watch the right rear. Do both shocks collapse at the same rate? Meaning do they both bottom out at roughly the same time? Technically they should but some chassis have different angles designed into them. We’ll get into that soon.
Lets say they dont, lets say your left rear spring collapsed faster then the right front you picked up. The angle your RF shock is at is in the shocks effective range more then the LR is. Meaning you used more of the shock then its fulcrum, it didnt just pivot on the chassis. So now take your rear shocks and stand them up one hole, move them back one hole on the chassis. Doing the same drop and lift now what happened? Notice a change in the rate at which they reacted?
Heres another way you could change that same scenario. Put the rear back in its original chassis location and move the front shock back one hole laying it down a little more. Notice the front got a little faster collapsing then the rear now, a little softer? You are simply working on finding an effective range for your shocks and springs.
Steering off a bit Im going to touch on something else to watch, Articulation! Laying a shock down will gain articulation. But like we mentioned theres a balance between a shock falling out of its effectiveness and staying in its linear range. Ideally you want to find where your shocks balance while collapsing and giving you enough articulation.
Our opinion on shock angles is find the balance where they both collapse at vitrually the same rate BUT ….. find it with the rear shocks angled slighty more then the front. This tends to help with articulation.
This is where its not as simple as using certain holes just because everyone else is. Every driver is different, every chassis is different and terrains may call for a different setup. This is where you have to tune for your style and terrain and learn what the shocks are telling you.
Think of it this way. Shocks work together with each other on opposite corners. If a rear shock collapses before an opposing front then you are taking away from the front doing its job too. You are loosing traction on the front or vice versa.
Playing with angles on matching springs is a great way at first. Changing spring rates is a good second way to find this balance if angles are too drastic when doing this excercise. But remember you dont want to go too far in spring rates. We want to find a balance idealy with equal springs or one spring rate apart.
So you have played with your shock angles and found a good balance of springs and articulation. You found a point you are happy with, remember those mounting locations. Now comes the fun part, oils.
Oils help control a shocks reaction to terrain changes and weight transfers. Remember what we said in the very beginning, ”opposite corners work together”. Ok before you guru’s and veteran drivers jump on us YES we know shock valves play a good role too. For this we are just keeping things simple for the sake of helping. We will touch about pistons a little towards the end.
Oils can help adjust for spring rates also. Lets say we have a setup where you went through and played with various springs and you still cant get a good balance with shock angles. Lets say your rear is too soft compared to the front so you went up a rear spring but thats too much. A thicker oil in that softer shock can help make that shock react slower, more resistance, and compress at a similar rate to the opposite shock.
We see this often in chassis’s that have rear shocks layed down a lot more then the fronts. Some drivers, or terrains, may like a lot of articulation in the rear but drivers keep adding heavier springs to stop them from collapsing too fast. Also some chassis’s are designed that way depending on the designers personal theories.
A great example is drivers using SCX shocks on their trucks and laying them down to what seems virtually flat when articulated. They tended to run shock oils upwards of 80-100wt oils in the rear. This essentially made up for the smaller body shock (less oil in it) and the fact the shock was out of its effective range. No it wasnt because the SCX shocks liked to leak, it was to keep the shock in a range of feeling linear vs falling.
But with our excercise of finding a balance with angles and springs we are more in the shocks range. Lets start with a base line oil of 35wt in SCX or 30wt in Traxxas/Dravtechs, any brand oil will work. This is where it can get a little tricky/painful and practice is needed.
Do your shocks seem to collapse like they did with no oil? Opposite corners are relatively collapsing at the same rate? No? Maybe try a thinner oil in the shock thats slower or heavier in the faster shock. Usually we end up going thicker in the faster shocks first. Also you can try pushing the chassis down so all 4 shocks are collapsed then let it rise up on its own. Did one end come up faster? That is telling us those shocks need a little thicker oil.
This part is just for example but hopefully will help with ideas of how to read your shock. Drive up to your obstacle at an angle, try to climb that left front tire up first. Does your front shock collapse as you climb up it? Or does it stay stiff causing the right rear to collapse before the front does?
Heres how we look at this situation …… Left front seems stiff and drives up with out collapsing. Our right rear started to collapse first and when we get half way up the front then begins to collapse. Our front oil is too thick or our rear is too thin. The shocks are not balanced for our liking. But we need some other terrain spots to see how they react. Now we approach a drop off and we see our front drop over it and then our rear appears to extend to fast. Our rig wants to topple the rear over the front. Yup our rear is too thin, it unloaded too quick.
If we just looked at the first part of that paragraph we would have solved one problem but not helped the drop off problem. So in our experience we know its the rear oils. Our weight is transfering too fast to the rear on a climb and unloading too fast on a drop. We would go up (depending on how we saw it happen) one weight in oil for the rear. From 30wt we could go to a 35wt to slow the rear down.
A common mistake we see drivers do in a case like this is add preload to the rear spring or even go up one spring rate. We call it a mistake because you just put yourself outside of the shocks balance and didnt fix the problem, you just band aided it and hurt other parts. They stiffened the spring up for compression but now the spring has too much load and wants to release it faster.
We would watch a few practice packs to really get a sense of what the shocks are telling us. Generally you can get a feel for what the shocks are saying right away. You could also play with shock angles first and see the effects. Same scenario but we are not tearing shocks apart in the woods. Try laying your front shocks down one hole or standing the rears up one holes. Laying the front back one hole would soften them up a bit and may be a sweet spot for your style.
Now lets flip things and say the front collapsed first and the rear stayed extended longer. A benefit is the rear is keeping weight transfered forward for traction but theres always a loss to a benefit. Now when the rear tries to climb up its too stiff. It isnt soft enough to let the rear axle gain traction and bounces around. Or on a drop we see our front end collapse and again the rear is too stiff and wants to topple forward. Or in off camber situations we may see the rear slide or worse not let the truck stay low and falls over.
Its a tough line to decide what way to tune but worth the aggrevation finding that sweet spot that fits you and your truck. Like we said, not all setups are the same nor are terrains. Understanding what your shocks are telling you can help. Expecially if you are a traveling driver and run something on the west coast vs the east coast.
Another thing to look at is vehicle weight. Many years ago we all mostly ran 5-6lb trucks. Once we started going to feather lites as some call the trucks in the 4lb or less range we found shock tuning played a big roll in weight transfers.
A 5lb truck is going to throw its own weight around more then a sub 4lb truck so we may need that oil to slow it down. Now a feather lite will need to get that weight transfered quicker. The same oil as a 5lb truck can make a feather lite too stiff to terrain changes. We hear drivers say things like ‘the front takes too long to settle down’ or ‘the rear doesnt flow smooth and likes to push the truck over’. All tell tale signs the oils are wrong.
Something else to remember about going too thick with oils is this. A thicker oil may make that shock compress slower, add some resistance to the opposite corner. But when that shock is compressed and the terrain changes, that shock is going to react slower too. You may need that weight to be transfered back to the opposite corner faster. That heavier oil is going to slow that transfer down. One benefit caused a loss elsewhere.
When ever building your shocks and changing oils to tune we always check our balance. Even when I get to different spots I personally always articulate my trucks to see how the shocks feel/collapse. This tells me my base line balance and that my preload and oils are good. From there I know Im at a neutral setting and can adjust a little preload if I feel Im too soft or stiff. Its just something I do for self confidence in knowing my truck will react as I need/expect it to.
Now a bit of a touch on shock valving. As technical as I can put this and still keep it simple is this. The more oil you can flow ‘through’ or ‘by’ the piston the softer the shock will be. Example using the same oil ….. a 3 hole piston for types like Traxxas/Dravtech will flow more oil then a 2 hole. Its pretty simple physics, the less restriction you put on a fluid the faster an object can pass through it. Same thing in priciple for a SCX shock using the stock flower looking valves vs the machined ones we (Krazed Builds) make in various designs. Our delrin machined pistons come in various designs to effect the way the valve allows oil to pass by it, the piston to move through it.
When playing with pistons it can be a rabbit hole that has no bottom. It can be tough to find the right balance. This area of tuning can be useful when you find yourself stuck between too soft or too hard of a shock oil. For example lets say your 3 hole piston is too soft with 30wt but too stiff/slow with 35wt. You could try changing that piston to a 2 hole and staying with your 30wt as a better balance.
Or lets say your SCX shock with our 4 notch piston is too soft with 45wt and 50 wt was stiff. You could try changing to the blue flower looking ones and find 40wt to be a better feel. The difference in these would be the surface area the oil has to flow over/by. Its really a game of finding what works for you but like I said, chasing pistons can be a road with no stop signs.
The reward is worth the work though when it comes to shocks. Once you find the balance your style and truck likes its easy to use that knowledge on all your trucks. Things to think about are what type of terrain am I putting it on. Is it a scale truck vs the comp crawler. What weight range is my truck going to be in, is it gonna be 4lb or less or is it gonna be loaded with brass and in the 6+lb range. What setup did you put on a similar truck and how did it feel. What are your goals for your current build or setup. All helpful questions when it comes to oils and pistons.
Theres a lot more that we could get into about shock building and tuning but we wanted to keep this simple. we wanted to bring forward something we’ve done for years when it comes to shocks.
We hope this helps some of you when it comes to shock tuning. Thanks for reading.