pirape

Hi
I read a lot of threads of people using from 500 wt to 50,000 wt in the diff

some using grease...

I know a lighter oil will result in a sensitive diff

I would probly feel the differance between 500 and 50,000 but what about

20,000 and 30,000?

But my main question is how do I know its right?

burnineyes

iTrader: (17)

You are tuning the rear tires to give you the traction you need. You will probably not notice going from 20K to 30K, but going from none to any you should see a big difference. As for when you know its right? Thats going to be all about the feel. You'll want maximum traction for acceleration, but too heavy an oil and the rear end will slide around corners too easy and you will feel out of control. The right amount will make the rear end feel more planted but still turn good, and this could change with track conditions or driving skill. I would start with something like 5-10K and go from there.

pirape

I bought oil... Do you have to fill up the diff completely?

GSMnow

Are you taliing about just a rear drive 1/10, or a 4WD with 3 diffs?, 1/10 or 1/8? Buggy or Truggy?

I will assume electric since you are on this heading, but are you using motor braking only, or do you run a brake servo?

I know that is a bunch of questions, but it all makes a difference on where you want to start, and like was already stated, the course, grip, and your driving style will all effect what works best for you.

Light oil in the back will allow for quicker steering, going up a little will calm it down and reduce oversteer, but go too thick and it will cause oversteer as the tires skid a little when the car rotates. Any time you go thicker on a rear diff, put the car on a slick area of the track, or a surface with similar grip, lift the front tires off the ground and turn it side to side, the rear tires need to rotats and not slip on the surface.

The front diff on a 3 diff car acts quite diferent than the rear. Going light in the front diff will allow the inside front tire to "diff out" when you try to accellerate. The lightly loaded tire will just spin and little power will be put down. If our center diff has any oil at all, this will put the power to the rear tires and make the car loose as well. Almost every one I know runs oil a bit thicker in front than in the rear. Thick front oil to a point gives the car alot of steering when you get on power coming out of turns.

Center diff?? This one can get a bit odd. I amnot finding a lot of agreement either. Around curves, the center diff still sees a very small speed difference. If the car is going at a speed where the tires are not slipping sideways uch, then the front tires are taking a slightly longer path, but the difference is far less than the differrence from left to right side. As your corner speed picks up, and the rear tires starts to generate slip angle, the path of the rear tires increases and at neutral steer, the front and rear tires will travel very close to identical distance, so the center diff is not slipping at all. This small speed difference inthe center diff makes it far less sensative to the oil, and a bigger change is needed to feel it.

Using motor brakes on a 3 diff 4WD throws in another issue. The center diff is now also your brake bias as well as controlling the power. Too light and the rear tires will possibly lock up and even spin backwards and the car will get super loose under braking. As you go thicker, the front tires will take more of the braking force. This will stop the car faster but also go towards push under braking.

My current setup in a very balanced 1/8 E-Buggy is 7,000 front, 20,000 center, and 3,000 rear. I am not saying this is perfect for any buggy or surface, but it is working for me. I have a bit of push under braking, but it really hooks up hard under acceleration with very little front tire ballooning. IT will get a little loose on drop throttle, but get very tight on power allowing me to get on the throttle very early out of turns. I am tempted to go a little lighter in the center and/or rear to get a little more off power and braking rotation, but I need to be careful to not make the car nervous and too quick for my reaction time, right now the car is easy to drive o it's limit making me very consistent if not the fastest. A faster peak lap will not help much if I can't do it every lap.

pirape

Sorry and thanks

Its for a 1/10 kyosho ultima SC (rear wheel drive) I wanted to try different than my ball diff since I cant get it to work properly

I have now filled it up completely with 30,000 wt oil and I have tryed it on pavement for 2 runs... I can tell you that I hate it when I turn at higher speed the car does a 180

It didnt do it as much with my ball diff..

Does that mean I should go lower oil?

I am missing cornering I woud like to do faster tight turns

should I try 3,000?

x60Driver

iTrader: (4)

Well first off what are you doing, just bashing? Race you also racing, high speed runs?

pirape

I am racing I did an highspeed run to turn at full speed to see how the rear would act

and ball diff was acting better than a gear diff with 30,000 wt oil in it...

I also wanted to know if I should completely fill the diff or just couple of drops?

GSMnow

Fill the diff almost all the way, you need to leave a little air space, or it will leak out somewhere.

For a lighter rear driver only like that, I would start at just a 1,000 to 5,000 and see how it feels. A good ball diff is very smooth and acts like a very light oil, probbaly no more than a 2,000 in a 2 spider gear diff, maybe even lighter in a 4 spider gear diff.

As far as getting more steering, you need ot be a bit more specific. There is nothing that will make a car turn a 90 degree corner at full speed. Even with perfect tires for the surface, you are not likely to get more than 1G of grip, 1.4G is possible if the tires can dig in but then you are looking at a traction roll over as well. Is your "not enough steering" a problem on a race track? Are you class competitors faster arouf the curve in question? Describe the track layout and the corner you are having trouble with. Is the problem a push where it just does not turn sharp enough, or is the tail swinging out on you. Is the problem at corner entry, steady turn, or corner exit?

The stiffness of the dif can fine tune some areas of the turn, but there are several different suspension adjustments that will each effect different areas of the turn. Once we understand what you are trying to do, we can likely suggest things to try. Keep in ind though, some times you just have to slow down to take the right line though a turn. The current layout at Hot Rod has a section like that. It just plain feels like you are going so slow to make a good run around the "wagon wheel" as the spokes just upset the chassis too much and force you to take a much longer wide line if you try and go at more than a crawl pace.

pirape

I will try that! thanks but what I meant was when I was accelerating out of corners the rear of the skids and sometimes gets me backwards... I was trying to minimize that effect.

I wanted to go to gear diff because of the low maintenance

so 1000 to start?

KevMc

iTrader: (27)

Some great tech here. I just now have my first 4WD with three diffs and I am trying to educate myself on how the viscosity affected handling.
Thanks GSMnow.

GSMnow

With just rear drive you are really asking a lot of the rear tires. There is a limit to how much power you can put down without breaking the rear tires loose. A lighter rear diff will allow the inside tire to break loose first, and may help some, so yes, 1000 oil in the diff will be much easier to manage than the 30,000, but may not be enough to make it any better than the ball diff in this situation. What you really need is to maximize the grip of the rear tires. Are you totally happy with the handing in opther places on course? Do you have any long steady turns to deal with? If so, is the balance good, or does it get loose or push? One trick I found that really helped in my XXX-T truck was putting down travel limiters in the front shocks. If set right, they will have little effect on the rest of the track, but when you accelerate out of a turn, the front end will hit the pu limiters, and if the car is still leaning, the inside front will hit first, making that tire get light, this helps keep weight on the inside rear tire while loading the ouside front more. This induces a moment of understeer instead of spining out or high siding. It is not a miracle cure, too much power will still upset the chassis, but it can give you that edge when you are trying to catch or hold off your competition. If the car is loose in steady state as well, then add a front sway bar. I also have than my my XXX-T. Lighter oil in the rear shocks can also help with dynamic grip, but you need to balance that with what it is doing on corner entry. Too light of rear shocks will hurt rotation under drop throttle. Light front shock oil on the other hand will give more grip on a rough surface.

Hope this helps.

GSMnow

I was new to 1/8 3 diff myself just a cpl months ago. I am stil learning the finer details. If you hunt around, you will likely find my previous threads talking about this. I learned a lot. I still have some of the hot fast guys telling me to go lighter in the center diff, and maybe even the rear diff, but I have it responsive enough for my driving skill level now. Lighter center will make it looser under braking as well as allow the front tires to unload and spin under acceleration. If you are just motor braking, I would start with no less than 7,000 in the center, and I am really liking the 20,000 in there, but different diffs and vehicle weight will effect what works best. Just keep in mind what it is doing, and work on understanding what change will do what you want.

KevMc

iTrader: (27)

My 3 diff rig is an Ofna Hyper10SC truck. I have it at 5K - 10K - 3K front to back but I have not yet had any track time with it, just going off other's suggestions so far until I can go practice and work on my setup some this weekend.
Thanks again.

bschanz

iTrader: (3)

i have 10k weight in the diff on my slash and 50 wt in the rear shocks. it seems to hook up much better that with the grease in the diff and 30wt in the shocks. in the wet loamy stuff, that most of our track is after prep it hooks up very well when entering a corner at low or no throttle. once the truck gets into the apex, i can give it throttle and is begins to rotate, then i can hammer on the gas and it grabs and goes. There are a couple spots where it dries out quicker and those areas are a little tougher to negotiate sometimes but all in all, the trcuk handles very well with 10k in the diff.