Shock Rebuilding ? About Oil Wt.

[Phins Fan]

As the title states I'm starting to go thru everything I have and will shortly be starting suspension work on all my vehicles (I neglected them during the entire season last year) I have already ordered rebuild kits for all of my shocks and need to know about shock oil wt. I'm thinking that it would be assumed that a rock crawler would not take the same type/wt oil as say an 8ight. So my question would be what is a basic rule of thumb when putting new shock oil into your shocks as far as wt for specific vehicles? Would a crawler take say 30wt/40wt and an 8ight take 60wt/70wt or the other way around and why?:thankyou:

 

[Phins Fan]

TTT. Anybody? Just lookin for basic rule of thumbs here.

 

[alien13]

A lighter weight oil is going to make the shock react faster. With a heavier vehicle you might want a thicker oil to prevent it from bottoming out, or to keep the shocks from compressing too fast. In my XXX-SCT I use 32.5 wt oil, though I'm considering a heavier oil in the front to keep it from squatting too fast going into the corners.

 

[Phins Fan]

So would it be safe to say a lighter vehicle may be better off with a lighter oil and a MT utilizing a heavier oil due to the weight alone?

 

[2revo1maxx]

The springs hold the vehicle up and the oil does the dampening.
The suspension should sag a little under the vehicles own weight.
The type of piston also makes a difference. By switching pistons you can get different results with the same oil.

 

[Phins Fan]

The type of piston also makes a difference. By switching pistons you can get different results with the same oil.

Not knowing alot about them, would the piston be the "white spacer" inside the shock with a couple holes in it? I would imagine changing this from 1 to a 3 hole setup would allow faster transfer of the oil and vice versa correct?

 

[alien13]

Not knowing alot about them, would the piston be the "white spacer" inside the shock with a couple holes in it? I would imagine changing this from 1 to a 3 hole setup would allow faster transfer of the oil and vice versa correct?

Yes, some differ by hole size, not count though.

---------- Post added at 5:11 PM ---------- Previous post was at 5:08 PM ----------

Here, it's alot to read, but it helps to understand what you're doing.

Shock Absorbers

Shock absorbers and springs are universally the most misunderstood, yet critical part of any car suspension - particularly an off-road R/C buggy. When your car can be jumping up to three feet into the air and flying anything up to 10 feet before landing, it's important that your shock absorbers and springs can control the car on landing. The difficulty is that those same shocks and springs have to help the car get around corners, and manage over innumerable smaller bumps, ruts, holes and lumps of rock and dirt. Sounds like quite a feat! Perhaps more than any other part of the car setup, choosing the right combination of shock absorber and spring setup is a compromise. You need to weigh very carefully the need to get the car through the corners - for which low ride height, stiff springs and 'hard' dampers can help - with the need to help the car soak up bumps and jumps (high ride height, softer springs and lighter damping!). Let's start by taking a look at the shock absorbers and how they work - what each adjustment does.

It is the shock absorbers' job to control the car's suspension. While the springs keep the car off the ground, the shocks must control, or slow down, the spring's action. Just how much to slow down that action is the great dilemma in setting up shock absorbers.

A shock absorber typically contains a number of parts: the shock body keeps it all together and contains the shock oil; the shock shaft protrudes from the shock body and connects the piston at one end, and the suspension arm at the other. Shock seals keep all the oil on the inside (where it belongs), while the volume compensator makes allowance for the oil that is displaced when the shock shaft and piston enter the shock body. The 'damping' effect of a shock absorber comes from the resistance of the piston to moving through the oil-filled shock body.

The variable parts of a shock absorber are the length of the overall unit, length of shock shaft, travel limiters on shock shaft (both inside and outside the shock body), the piston attached to the shock shaft, and finally the viscosity (thickness) of the silicone shock oil used to fill the shock body. Let's take a look at each of these adjustments and the likely effect on your car.

Shock Oil

Shock Oil is the simplest, most universally used adjustment to the shock absorber. Using thicker shock oil will help to 'slow down' the suspension motion of the car while lighter oil will do the opposite - letting the suspension react more quickly to the demands of the track. Thicker oil is most often used when track conditions are smooth, and hard packed and traction is high. In these conditions suspension movement detracts from the handling of the car.

Thicker oil is also useful for controlling the car when landing off big jumps. When the going gets rough - if there are numerous ruts and holes or a lot of small jumps, or if the track is particularly slippery - lighter shock oil should be used. This will let the car react more quickly to the track - helping to keep the tires in contact with the track.

Shock oil viscosity (or thickness) is measured in 'weights'. The higher the number, the thicker the oil. While most companies' shock oil is reasonably close to each other's, there are some slight variations. Why? I have no idea! The solution is to try and always use oil of the same brand. It doesn't particularly matter which brand of oil you use, but you should try to always use the same brand.

Shock Pistons

Shock Pistons are a bit of a black art as far as many racers are concerned. Variables in shock pistons include the size, and number of holes in the piston. Pistons with larger holes allow the shock oil to travel through more quickly, while smaller holes will slow the travel of oil through the piston. The difficulty is in knowing how to using this adjustment. In most conditions, your car's standard piston configuration will be fine. When the track is particularly rough, with lots of small to medium bumps and holes, pistons with larger, or more, holes will be helpful. When the track is smooth, or if it has big jumps or drop-offs, smaller holed pistons could be the way to go.

What is important to remember is that pistons and shock oil have a very close relationship. Sometimes if you change one, you need to change to other. An example of this would be that when fitting larger holed pistons to your car your should probably use slightly thicker shock oil. Most manufacturers offer a range of pistons for their shock absorbers and there are a number of aftermarket alternatives.

Alternatively, some drivers have taken to drilling different sized holes in their shock pistons. This is particularly common amongst team drivers to make very small adjustments. Such fine adjustment is not really necessary for the majority of us and should be left as a last resort. Similarly, the use of 'dual stage' pistons which have a different action on the up stroke when compared to the down stroke is probably not advisable for drivers early in their R/C career. If you wish to try some of these options - then it is probably best to consult the local 'pro' driver. They'll be happy to help you figure out what to try.

Travel Limiters

Travel Limiters are small spacers placed over the shock shafts to limit the travel of the shock absorber. Limiters placed outside the shock body limit the 'up travel' of the shock absorber, while placing spacers inside the shock body limit the down travel (and hence overall length) of the shock absorber. This is not an adjustment commonly used - once set it's usually forgotten.

Adding travel limiters to the inside of the shock absorber can be particularly useful on a very smooth track, while a track with big jumps will probably see some drivers adding limiters to the outside of the shock absorber - to prevent 'bottoming out' of the chassis on landing. Again, this is an adjustment not commonly used in the early stages of your racing. Set the shock limiters according to the manufacturers' suggestions and you'll be fairly close.

Shock Shafts

Shock shafts can sometimes be changed to longer, or shorter units if more, or less overall travel is required. This type of adjustment is used only very rarely or in extreme circumstances on a very small range of cars. Again, the best advice is to consult your local 'pro' driver and see whether they are using longer, or shorter shock shafts.

Springs

Springs are a very useful adjustment for the suspension of your car. Springs vary in length, and 'stiffness'. A 'stiffer' spring is harder to compress between your fingers than a 'softer' spring. Stiffer springs will tend to hold the car up off the ground more, while softer springs can allow the car to ride lower, and to 'roll' from side to side more.

Springs, Jumps and Bumps

Springs are often changed to reflect the size and shape of bumps and jumps on a track. If your track is relatively smooth with lots of big jumps, you should try a slightly stiffer spring - to help the car land off jumps without bottoming out. On the other hand, if the track has lots of bumps and ruts, but no real large jumps - you can try a softer spring - to let the suspension soak up the little bumps without effecting the chassis balance too much.

Springs and Handling

Oddly enough, the springs you choose can have a large impact on handling of your car. Changing to stiffer springs will generally result in lower traction at that end of the car - e.g. putting a stiffer spring on the front of your car will often give you slightly less steering while adding a softer spring to the rear can give more rear grip - to a point. Amazingly, in some conditions, the opposite can be true - stiffer springs can add traction.

If you are racing on a high traction track, sometimes adding a stiffer spring can give you more traction by helping the suspension to keep more pressure on the tires. Remember this one if you're on a high traction track. Most importantly remember that when you're choosing springs - there's a compromise between handling and ability to cope with bumps and jumps. You've got to experiment a little to find the right combination for each track!

Spring Clips and Spacers
Many people adjust the 'compression' or 'pre-load' of their springs by either adding spring clips to the shock body, or moving the 'spring collar' up or down the shock body. This adjustment is only for adjusting the ride height of your car. Adjusting the spring compression does not 'stiffen' or 'soften' your springs. For more discussion of ride height and its effect on handling see (Suspension Geometry).

It's good to have a range of springs to choose from. Most manufacturers color code their springs to help you identify stiffer and softer springs.

Shock Mount Positions

R/C cars offer differing standards of tuning options from manufacturer to manufacturer. Almost without exception they all offer alternate mounting options for shock absorbers. Mostly, the options relate to the distance along the suspension arm that the shock mounts, or the angle of the shock (by altering the top shock mount position). These two options provide various responses in terms of the handling of your car. Let's take a look:

Moving the bottom of the shock along the suspension arm basically affects the 'stiffness' and 'drop' of the suspension. Moving the shock mount further out results in a suspension that appears both 'stiffer' (sprung) and 'harder' (damped). Conversely moving the shock inward gives a softer feel. The reason for this is simple. The easiest way to explain this is to think back to the playground seesaw of your childhood. Remember that even if the people on either end don't weigh the same - simply by moving the heavier person closer to the center - the seesaw can be made to balance. It's simply a question of leverage. As the shock moves out along the arm, it can bring greater leverage to bear on the suspension arm. Moving the bottom of the shock along the arm also affects the suspension drop - further out equals less drop, further in equals more drop. Suspension drop is covered in depth in another Section of this book.

Moving the top of the shock absorber has a more subtle effect on the car's suspension. What is changing here is the angle of action of the shock absorber. Changing the angle makes the shock absorber more, or less, progressive. A progressive suspension setup describes the situation where the suspension becomes stiffer as the shock/spring/suspension is compressed. Leaning the shock absorber over further results in a more progressive suspension. This is useful in landing off big jumps (helps stop the car from bottoming out), handling on smooth tracks, handling in high-speed corners. Standing the shocks straighter helps in rough conditions, or tracks with lots of quick changes of direction. Adding interest to this setup option is the fact that leaning the shocks in gives some degree of anti-roll effect while standing them straight up encourages, or allows, more chassis roll. The shock angle you choose can thus be closely related to the use of an anti-roll bar.

 

[Phins Fan]

Appreciate it alien but I certainly hope you just copy and pasted! if not hows your carpal tunnel doin?

 

[alien13]

Copy/Pasted it. I have a whole setup guide that I refer to for racing.

And the carpal tunnel was bad long before this.

 

[2revo1maxx]

Quote: And the carpal tunnel was bad long before this.

Sounds like you gotta get away from your computer once in a while.

 

[Mn Monster]

great info! thanks! my shocks are all messed up my maxx. this will help a ton !

 

[alien13]

Quote: And the carpal tunnel was bad long before this.

Sounds like you gotta get away from your computer once in a while.

Actually it's the work I do. I'm a semi-trailer mechanic. Replace one side panel and that's 500 holes drilled and 500 rivets bucked in. Tons of repetition and vibration. Fourteen years of that takes it's toll.