Silicone Oil guide

[Fly In My Soup]

After polluting a members thread with my nerdy waffling!...I'm going to pen some facts about silicone oil... And how it's use in RC came about..

 

There's a lot of misleading info on this subject, sadly some seems to originate with the RC manufacturers themselves....

 

I'll attempt to clear up any questions with this thread.

 

A brief history;

Back in the early 1980's shock absorbers where smaller, and usually filled with transmission oil, or even stp oil, which had to be preheated with a heat gun before racing!

Due to impracticalities and it's inherent temperature viscosity changes, stp oils, where abandoned in the mid 1980's in favour of silicone oil, which we still use today, due to silicones ability to withstand a wider temperature range without the viscosity being affected.

Silicone oil also replaced grease in diffs thanks to o-ring sealed diffs, this happened later on in the early 90's.

 

The basics;

As a rule, the higher the CST or Wt number, the more viscous (thicker) the oil is.

 

The official (world standard) unit of measure s.oil viscosity is in Centi-Stokes, abbreviated to CST, or sometimes Centi-Poise (Csp).

 

Wt is a unit of measure invented by American RC company Team associated, and their supplier Lucas Oils, most other American RC companies followed suit and use Wt also.

 

 

What is a Centi-Stoke/Centi-Poise/Wt unit;

 

Centi-stokes- is the unit used to measure the oils DYNAMIC viscosity (the fluids resistance to flow,)

 

Centi-Poise- unit used to measure KINEMATIC viscosity ( the fluids ratio of viscous force to its interial force.

 

Wt- is simply an abbreviation of the word Weight.

 

 

So can I compare the thickness of WT to CST?;

 

It can be done yes, but only by a technician in a lab using a rheometer or similar.....you cannot simply say;

 

"40Wt thickness oil is comparable to 400cst, or 60wt is like 600cst"

 

It doesn't work that way...

 

As Wt scale of measure is not linearly comparable to CST, even some WT oils aren't comparable with each other!!...e.g Losi 40Wt oil is like X-rays 42.5Wt

 

This is because, as discussed earlier, Wt is not a standardized measure.

 

So how do we actually compare Wt viscosity to CsT?;

 

As already noted, the only true and correct way to compare Wt thickness to CST is to use a rheometer

There's a few different kinds of rheometer, so I'll keep it simple.

 

Rheometers simply measure the way a liquid flows in response to applied force.

 

So what oils from what companies have been rheometer tested and compared Wt to CST;

 

A few have been tested, and Wt compared to CST, although more work needs to be done in this field IMO

 

Here below are some I found

 

In this table you can see even Losi and team associated Wt differs

 

 

Below is a more recent test which not only displays the viscosity comparison between CST and Wt but also displays a difference in Wt oils themselves

 

 

Here's a small comparison table from core RC (Schumacher), which was a small scale test to see how they're CST converted into Wt figures

 

 

And lastly, after 2006, x-ray changed oil supplier, so a full rheometer test was carried out , not only comparing their respective Wt rated oil to the new , but also what theirs, and others, Wt oil converted to in CST

 

 

 

 

 

There are tables out there, please feel free to post them if they're relevant...BUT only if you can confirm the testing has been done by a rheometer in a lab

 

I'll post more 'shocking' info later, pardon the pun....

[Gavster29]

This is great info thank you for posting!

So being a noob when it comes to oils what should we be aiming for in diffs and shocks, I'm guessing for accuracy and the fact that most oils are CST then some guidance in CST would be really helpful?

Sent from my TA-1033 using Tapatalk

[Fly In My Soup]

1 minute ago, Gavster29 said:

This is great info thank you for posting!

So being a noob when it comes to oils what should we be aiming for in diffs and shocks, I'm guessing for accuracy and the fact that most oils are CST then some guidance in CST would be really helpful?

Sent from my TA-1033 using Tapatalk
 

 

That would depend on what setup your running to be fair.

 

What scale of model, type of propulsion (nitro,petrol,electric), type/brand/model of shocks/springs

[Fly In My Soup]

3 minutes ago, Gavster29 said:

This is great info thank you for posting!

So being a noob when it comes to oils what should we be aiming for in diffs and shocks, I'm guessing for accuracy and the fact that most oils are CST then some guidance in CST would be really helpful?

Sent from my TA-1033 using Tapatalk
 

 

That would depend on what setup your running to be fair.

 

What scale of model, type of propulsion (nitro,petrol,electric), type/brand/model of shocks/springs

 

If it's for your hyper 7 b.less then I'd go for 7000cst in front, 25,000cst in the centre, and 5000 in the rear....

 

That would depend on what kind of power system your running....What kv motor, and is it 4s,6s etc etc

 

For your shocks...Would depend on weight of your rig, shocks/springs used etc

[.AJ.]

Nice guide, I'll make it a sticky  

[Fly In My Soup]

Cheers dude

[Gaz!]

@Fly In My Soup, thanks for taking the time and input into this thread. It really is appreciated 

[Gavster29]

 
That would depend on what setup your running to be fair.
 
What scale of model, type of propulsion (nitro,petrol,electric), type/brand/model of shocks/springs
 
If it's for your hyper 7 b.less then I'd go for 7000cst in front, 25,000cst in the centre, and 5000 in the rear....
 
That would depend on what kind of power system your running....What kv motor, and is it 4s,6s etc etc
 
For your shocks...Would depend on weight of your rig, shocks/springs used etc

I was after more of a general guide, say 1/10 scale should be blah 1/8 should be blah or something along the lines of bashing go with a thick oil for road use go for a thin oil?

Finally can you damage a diff by going too low?

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[Fly In My Soup]

42 minutes ago, Gavster29 said:

I was after more of a general guide, say 1/10 scale should be blah 1/8 should be blah or something along the lines of bashing go with a thick oil for road use go for a thin oil?

Finally can you damage a diff by going too low?

Sent from my TA-1033 using Tapatalk
 

 

Due to the variations in models, even models in the same scale, it would be hard to provide you with a general guide that would work well for all types of RC model....

 

As stated the weight, shock type, spring type, power system, gear ratio, type of diffs, even the layout of the diffs on the chassis would affect what CST oil you put in...

 

I think a more appropriate guide would be to advise on how the oil in a diff works, thus enabling you to make a more educated approach to your rig...

 

How does filling my diff with oil help me out?;

 

we will use a commonly used diff for our example....The gear diff.

 

A gear diff is what's known as an 'open' diff, an open diff works by applying power to the wheel with the LEAST amount of traction...Adding oil to the diff slows the gears down inside the diff, thus providing more power to the wheel with the MOST traction...

 

Real world example of how this helps me drive better

 

So i hear you say...Well how does increasing power to the wheel with the most traction more help?

 

Here's a situation....You're taking a sharp corner on some loose dirt, when cornering you notice that the outside tyre balloons as it looses traction, causing you to lose speed or control altogether..

 

It balloons because the diff is sending power to the wheel with the least amount of traction.

 

This is where using your diff oil as a tuning aid comes into play

 

Say in that instance you where running 2000cst oil....If you then replaced the oil with 4000cst the diff would be able send more power to the inner wheel, so when you next take a corner, the outside wheel wouldn't balloon as much....As the diff supplying the other wheel with more power, which = faster cornering, better handling

 

Oil Too thick or too thin

 

You may start to get the idea that it's a careful balancing act!

 

You want the thickness of the oil to be just right, put simply...

 

Too thin oil, your outer wheel will balloon out.

 

Too thick, you'll almost lock the diff up....If the oil is too thick, the diff sends power to both wheels evenly...Your RC will then understeer and may spin out (180°) easily on loose surfaces

 

Now you may see why pro racers and bashers a like care a lot about what diff oil to use, it really is important to get it right!

 

Most importantly, if your bewildered about where to start on refilling your own diffs and what to choose....A great base starting point is to find out what CST oil in in your diffs to begin with...

 

Then use your knowledge of how YOUR own RC drives and handles to decide which oil to choose from there what CsT replace the oil with based on how it currently drives

 

Hope that helps

Edited September 7, 2017 by Fly In My Soup

[Fly In My Soup]

44 minutes ago, Gavster29 said:

a thick oil for road use go for a thin oil?

Finally can you damage a diff by going too low?

 

You can for on road, as generally youre wheels have less traction loss.

 

Meaning you can run a thicker oil, as the diff doesn't need to do so much of a balancing act between which wheel to send power to.

 

You can indeed damage your drivetrain by using oil that's too thick or thin., I wouldn't worry too much...As long as you stay within the parameters of a normal CST range

 

 

[Gavster29]

Very helpful thank you! As soon as I'm back up and running I will play around with diff oils and hopefully understand what is happening!

Shocks I guess thicker less rebound so jumping would be better with a thicker oil but too thick and the truck will either break something as it has no give or corners would become a total nightmare with no give.

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[Fly In My Soup]

3 hours ago, Gavster29 said:

Very helpful thank you! As soon as I'm back up and running I will play around with diff oils and hopefully understand what is happening!

Shocks I guess thicker less rebound so jumping would be better with a thicker oil but too thick and the truck will either break something as it has no give or corners would become a total nightmare with no give.

Sent from my TA-1033 using Tapatalk
 

 

You don't make it easy for me!

 

You're on the right lines.....I'm guessing you know about setting rebound then?

 

My opinion on it;

 

Depends on the type of track/terrain, if it's bumpy and uneven I would run more rebound and thinner s.oil and go down a hole or two on the piston

 

Don't forget your pistons play a big role.

 

If it was smoother running terrain I'd go up to a 4 hole piston and thicker oil, less rebound.

 

Again, like the diff oil tuning it really is a personal thing, only you can find the right setup for your rig.... I say this because many people's RC'S (even ones of the same brand/model) have different setups entirely, like type of shocks, motor, tyres, foams, and obviously...what diff setup they're running!

Edited September 7, 2017 by Fly In My Soup

[MissT]

I'm staying out of this 

Edited September 21, 2017 by MissT
Spelling

[Fly In My Soup]

,To round this thread .... I decided to add this info...

 

What is silicone oil?

 

So you've been buying your oil and refilling your shocks and diffs...you know what it's called.....But you don't actually know what this viscous transparent liquid is....

 

Silicone products are manufactured by performing a process called polmerization 

 

What's polymerized mean?

 

It's a process, in this instance, in which liquid chemicals are added to the siloxane molecule to promote a chemical reaction, thus producing chains of polymer molecules....

Siloxane- above

 

 

These chains are called polymeric organosilicon compounds (organic silicone polymers).....They then further refine these compounds to extract the most important and widely used group of compounds called Polydimethylsiloxane (pdms)

Pdms- above

 

 

So why pdms?

 

It's used primarily for its mechanical properties, chief among which are it's unusual rheological (flow) properties and it's lubricating benefits.

 

So....

 

In lamens terms, they've replaced,eradicated all the carbon molecules in the liquid.

 

And that's how base silicone oil is made.

 

It's then an inert silicone liquid, which can be taken and optimised ( by then adding more carbon based or hydrogenised liquids) to adapt it for use in the hobby, toy, food, medical, automotive etc etc sectors.

 

You may not know it but silicone oil similar/identical to the oil in your rc shocks/diffs is all around you.....

 

Here are some of its everyday uses....

Cooking utensils, medicine coatings/pharmaceutical use,beer making,food additive,cooking oils,decorators caulk, replacement fluid during eye surgery, household cleaning products and thousands more...

 

Hope you enjoyed the brain fodder...

 

 

 

[Fly In My Soup]

Here's a Losi guide on refilling your shocks with silicone oil

 

 

[Fly In My Soup]

To help round the thread, here's a very brief guide diff oil tuning, text is borrowed not mine...

 

Some of these things have already been covered above.

RC diff oil tuning is very important. Here’s a guide to help you to understand how to set your diffs and how they work.

How diffs work:

Differentials are part of all buggies, truggies and monster trucks and their designs vary slightly from one vehicle to another. However their action and setup still the same. The center diff is the most important because it transfers power to the front and rear diffs. The front and rear diffs receive the power from the center diff and distribute the power to the left and right wheels.

Diffs are also very important when the vehicle is turning. When turning, the outer wheels spin faster than the inner wheels. Without the front and rear diffs, both wheels will be spinning at the same speed making cornering harder and increasing dramatically turning radius.

 

Understanding what happens:

Basically, diff transfers power to one of its outdrive. By design, the easiest outdrive to spin (with less resitance or traction) will receive the power. This also means that the wheel or the end of the vehicle with less traction will receive most of the power. This is where diff fluids are important. You can compare diff action to a lightning. The lightning finds the shortest route to hit the ground. In our case, the power generated by the engine will find (through the diffs) the shortest (and easiest) route to spin the wheels.

Differentials can be filled with different weight of silicon fluid. Depending of the manufacturer, the weight (viscosity of the fluid) varies from 1000wt to 100 000wt. The greater is the number, the thicker the fluid is. Some RTR vehicles come with grease filled diffs. Grease is equivalent to 1000wt diff fluid. The diff fluid “locks” or “retards” the diff action. A diff filled with 1000wt fluid will spin more freely and will transfer power to the “looser” outdrive faster than a diff filled with 50 000wt diff fluid. This will make the “looser” wheel or end spin and loosing traction while the opposite outdrive receive no power.

Some manufacturers have released different types of differential. At the opposite of the conventional diff, the Torsen diff transfers power to the wheel that has more traction. Losi recently released the SmartDiff, a system that “locks” the diff when accelerating and “frees” the diff when off power or braking. Xray also offers a similar diff called Active Diff.

Important note: Because diff action is all about traction, make sure you have the right tires for your track surface before experimenting with your diffs.

The center diff:

 

When accelerating, weight is transferred to the rear end of the vehicle. The rear wheels get more weight and by consequence more traction than the front wheels. The center diff will transfer the most of its power to the front wheels because they are easier to spin and will make the front tires ballooning. This reaction is also call, diff unloading. To avoid this situation, thicker center diff fluid will be the way to go. But going with thicker fluid will not completely stop the diff from unloading during hard acceleration. The idea behind center diff adjustment is to find out which fluid thickness will give you the best acceleration all around the track without scarifying performances.

 

The fluid selection must be thin enough to transfer more power to the front than the rear when accelerating. Why? Because you need your front wheels to have more power to help your buggy to exit corners and to track straight under acceleration. The fluid must also be thin enough to not send too much power to the rear wheels which will make your buggy over steer when exiting corners because the rear end will spin and loose traction. A basic center diff fluid weight for buggies is 7000wt and for truggies 10 000wt.

Thicker fluid in the center diff will make your rear wheels push the buggy while thinner fluid will make the front wheels pull the buggy.

To get the best from your center diff, don’t nail the gas. Go progressively with the throttle, this will prevent traction lost.

The front diff:

Changing front diff fluid directly affects on and off power steering. Thinner fluid will increase initial cornering and off power cornering. On another hand, if you go with thicker front diff fluid you lost initial cornering and off power cornering but gain when exiting corners. This is due by the fact that the inner wheel turns slower than the outer wheel. Thinner diff fluid “frees” the diff action and makes it easier for the diff to turn its two outdrives at different speed.

See what happens when you nail the gas while the front wheels steer left or right. The inner wheel will get the most of the power and will balloon. Thicker diff fluid will “retard” the front inner wheel ballooning effect. A good basic weight is 5000wt for a buggy and 7000wt for a truggy.

The rear diff:

The rear diff is the easiest one to tune. It should be tuned to be “free” enough to not decrease cornering but it should also be tight enough to prevent the inner wheel from ballooning. At low speed or off power, a rear diff with too heavy fluid will decrease steering because it is harder for the diff to rotate the inner wheel at a different speed of the outer wheel. A too heavy fluid will also make the vehicle fishtail when exiting corner causing over steer.A good basic weight is 3000wt for buggies and truggies.

When turning. the inner wheels spin slower than the outer wheels. The weight is transfered to the outer wheels.

 

If you want more steering entering corners, use:

• Thinner front diff fluid
• Thinner rear diff fluid

 

If you want more steering exiting corners, use:

• Thicker front diff fluid
• Thicker rear diff fluid

 

If you want more forward traction, use:

• Thicker center diff fluid

 

For better bumps handling, use:

• Lighter front diff fluid
• Lighter center diff fluid

 

Starting diffs setup for buggy:

• Front: 5000wt
• Center: 7000wt
• Rear: 3000wt

 

Starting diffs setup for truggy:

• Front: 7000wt
• Center: 10 000wt
• Rear: 3000wt

 

How much fluid to put into the diffs ?

If you overfill your diff, it will eventually leak. To make sure my diffs are filled properly, I first begin by filling the diff half way and then I rotate the diff gears to be sure fluid goes inside the gears. When fluid has made its way into the spider gears, I fill the diff until the fluid reaches about 1mm of the top.

 

Conclusion:

There is no perfect setup. One setup will increase forward traction; another will increase off power steering while decreasing speed when exiting corners.

It may take you many tests before you find out the good setup that works fine for you. Take your time and tune only one diff at the time. Begin with the center diff, followed by the front and by the rear ones. The harder is to understand what diffs do and how they react to changes. Once you get familiar, diffs setup will have no secret for you.

 

[DLD]

Very valuable info here, thank very much for posting.

 

I have tried different diff oil setups in the past, in various nitro buggies. To my experience, thinner Center diff oil makes the buggy easier to drive on rough, loose and short tracks. If I use thicker Center diff oil I get more acceleration and more 4WD effect, but to the cost of more instability and nervousness, especially if you run a high power nitro engine on your setup.

 

I lately run 5k - 5k - 2k on a crazy modded Hyper 7 TQ Sport (LTR ZR .30X) on a loose, dirty track and 5k - 5k - 3k on my Losi 8ight 3.0 buggy for racing (Front - Center - Rear).

I liked this kind of setup when I first used it on the Losi and  I kept it since.

 

Just my 2 c. _

[Kukynas]

simple translation of above for those buying oil in CST unit of measure

 

Starting diffs setup for buggy:

Front: 50 000 CST

Center: 70 000 CST

Rear: 30 000 CST

 

Starting diffs setup for truggy:

Front: 70 000 CST

Center: 100 000 CST

Rear: 30 000 CST

[Richard Anderson]

On 08/02/2019 at 15:00, Kukynas said:

simple translation of above for those buying oil in CST unit of measure

 

Starting diffs setup for buggy:

Front: 50 000 CST

Center: 70 000 CST

Rear: 30 000 CST

 

Starting diffs setup for truggy:

Front: 70 000 CST

Center: 100 000 CST

Rear: 30 000 CST

Hi there is this cst rate for a 1/8 and if it is how much less is it for 1/10 scale rate. I have got all of alloy upgrade to backwash pro 1/10 scale would I be better using the cst 1/8 silicon oil rate for my buggy diffs or go lower to the 1/10 rates for my diff only I have 450cst in rear shocks and 300cst in front shocks would this be ok I have not changed anything as I have just finished my build and upgraded it all to alloy not much plastic left onit now just the battery box thanks for any help kind regards Richard 

Edited January 30, 2020 by Richard Anderson

[zlab]

I am confused, some posts in this guide are talking about 3k/10k/7k cst for truggy, some are saying same numbers in wt and on the end we have 30k/100k/70k cst.

I never had oil in the diff before, i converted it to oil now and put in 3k cst rear/7k cst front. It is a FTX carnage without central diff. Haven't tried yet, as i am waiting for the new power system...

Which is now correct? Should i use 30k/70k cst instead of 10 times smaller numbers?

[Kukynas]

1 wt = ~10 cst 

so if you are looking for oil in “wt” units than 3k/10k/7k if in “cst” than 30k/100k/70k

[.AJ.]

Ive lived by this chart for years for shock oil, all diff oils are measured in cst 

 

[zlab]

So if all diff oils are in cst, why are some talking in wt and others in cst? I dont even see a 70k cst diff oil on EuroRC, only 60k and then 80k. Now i have 7k front/3k rear. Should i buy 80k/30k?

[Kukynas]

I think it's mainly due to fact people got used to using wt coz many brands were labeling their oils in this UOM, in general here's some  explanations https://www.rccaraction.com/silicone-oil-explained-weight-w-wt-versus-cst/

many options just choose different shop/brand, in general for Truggy anywhere between 50K and 75K for front should be fine, for rear usually 30K and center depends on the general behavior, I would start with 100K 

[zlab]

I don't have a center diff, i have a slipper clutch. Does that change a lot for front and rear? Honestly i am not a racer, just bashing it for fun. But you know, it is so fun upgrading it and spending money without my wife knowing it