Ok, so this goes back to the OP 2yrs ago. Lol.

A ball diff and a gear diff feel different on track and can have benefits on a given surface as a result of their function.

A ball diff and a gear diff have very much the same function off power and we all know that during a bend the outside wheel will need to rotate a quicker speed than the inside. This off power cornering and the cars “rotation” through a bend will be dependent on the viscocity of the oil in the gear diff, and the tightness of the thrust race spring on a ball diff. These can can be tuned accordingly.

The difference in their function comes when they are “on power”. During the bend, both diffs will bind on power BUT the ball diff will bind a great deal more.

The harder the vehicle accelerates the greater the ball diff will bind, effectively preventing the ball diff from a differential action.

The result is the reason that a ball diff is preferable on low grip. As you add throttle mid corner the ball diff binds, prevents a diff-ing action and drives the car forward. This will have the feel of weight shifting to the rear and potentially the loss of on power steering and helps prevent losing rear traction exiting a bend.

Alternatively the gear diff will still have a free (considerably less binding) action no matter how hard you accelerate and this can favour carpet or high grip tracks. Mid corner acceleration will have little effect on steering and the vehicle can turn much more freely. This can help you hold the inside of a sweeper at a greater speed than you could with a ball diff. The common phrase is “greater corner speed”

It should be said, as the OP had commented, the gear diffs action under acceleration of staying free, can be the reason why a vehicle with a gear diff can “diff out” compared to that of a ball diff.

Hope you find this helpful.

You might want to listen to this. Tristram Neal, Schumachers designer and the first manufacturer to put a ball diff in an RC car.

http://astateofrc.com/wp-content/upl...Trish-Neal.mp3

Some subjects survive the test of time better than others. Now that people actually get to choose between ball diff or gear diff as a tuning option, you can see why people will be Re-visiting threads like this one.

Well that depends on what end of the car we're talking about AND what weight fluid is in the said gear diff. Gear diffs with a greater volume of oil surrounding the planetary gears can be set with enough black mugen super grease so as to effectively lock them out - so there are significant variables.

But on a ball diff, you can't just lock the diff down with as much - or as little - diff screw action as you like. There's a fine operating envelope that the diff screw must remain within for the diff to work.

With gear diffs, the limits are down to whatever range of diff oils the racer has in his/her pit box.

How is this so? The ball diff uses balls instead of gears that are squeezed together between plates using a screw, spring and a thrust race. Planetary/spider gears are replaced with balls. How is it more likely to bind when more torque is put through it vs a gear diff? Again - a gear diffs performance under power is entirely dependent on the torque being transferred through a viscous fluid, selected by the user. If the fluid is thin, the diff will be more likely to diff out, or if the fluid is thick - less likely to diff out and feel more like a solid axle or spool. Depending on which end of the car we're dealing with, this can be used to increase or decrease on/off power steering.

Again, the ball diff's balls have no choice but obey the laws of physics here. If the torque passing through the ball diff exceeds the pressure/friction between the diff rings and the balls, it ceases to function as a differential and becomes a really expensive form of slipper clutch! :/ One that knackers your diff balls! Otherwise, it performs just like a ball diff would at any other time - the only diff limiting element being the tightness of the diff screw, which merely serves to put pressure between the diff rings and balls.

Well setup ball diffs, with nice round balls and diff screws that don't back out, can be a pleasure to use on slippery tracks. But what you describe here infers that ball diffs behave like limited slip diffs, which in my experience, they don't. Nor should they in theory, either.

Also, a diff that 'binds' - or to put it another way - 'starts to lock up', will tend to break traction on that axle. So in other words, on the rear diff, that would result in on-power over-steer. Or on the front, on-power under-steer.

Well again, this would depend entirely on the choice of fluid used in the diff. The thicker the fluid, the more like a solid axle it would feel.

Only if the car is balanced properly on the way into the corner and on the correct 'trajectory'. This is largely down to correct car set up and driver skill more than diff choice. A gear diff with the wrong choice of fluid will not be carrying greater speed through a sweeper than ball diff.

Diff out occurs when the power being applied by the motor/engine exceeds the traction of the tyres being driven. The tyre with the least traction will spin. With a ball diff, besides a little tweak on the diff screw, there's little you can do with the diff itself. Tyre choice is obviously the first thing to look at and also setting the slipper clutch to prevent wheel spin and diffing out in the first place.

With a gear diff, diff out can be tackled by going up in weight with the diff fluid.

With 3 diff cars, 4WD can very quickly become 1WD! Lol. That's why Torsen diffs were desirable on the centre diff on really loose, dusty tracks in 1/8th.

As with most things, it's all about finding the right balance between being able to put the hammer down in a straight line without losing power to wheel spin, whilst having enough differential action to negotiate corners well enough to get good lap times.